Glossary Terms


A proceeding wherein a shipper/consignee seeks authority to abandon all or parts of their cargo; railroad abandonment occurs when operation of all or part of a route or services is ceased, especially with the intent of never resuming it again; abandonment of an easement is the relinquishment of some accommodation or right in another's land, such as right of way.

A substructure element supporting each end of a single span or the extreme ends of a multispan superstructure and, in general, retaining or supporting the approach embankment.

acceleration lane
Drivers entering a roadway use this lane to increase speed so that they may safely merge with traffic.

access management
Measures regulating access to streets, roads and highways from public roads and private driveways.

The extent to which facilities accommodate persons with disabilities, including wheelchair users.

Accident Location and Analysis System (ALAS)
Computerized information available to engineering and law enforcement agencies.

active warning device
Flashing lights and/or gates used at railroad-highway grade crossings.

administrative law judge
A representative of a government commission or agency vested with power to administer oaths, examine witnesses, take testimony and conduct hearings of cases submitted to, or initiated by, that agency.

advance acquisition
The acquisition of real property rights for use on a transportation corridor in advance of the fiscal year in which right of way acquisition would normally occur; this is done to take advantage of favorable prices or the availability of land and to preclude further development that would make the property more costly to the public.

The horizontal and vertical definition of a roadway.

all-terrain vehicles (ATV)
Vehicle designed for off-road use.

alternate mode users
Individuals who choose a method of transportation other than driving a single-occupancy motor vehicle.

alternative transportation mode
This term refers to all passenger modes of travel except for single-occupancy vehicles, including bicycling, walking, public transportation, carpooling and vanpooling.

ambient conditions
The visual background or surrounding atmospheric and visibility conditions.

Americans with Disabilities Act of 1990 (ADA)
Civil rights legislation enacted in 1990 to end discrimination against persons with disabilities.

anchor span
The span that counterbalances and holds in equilibrium the cantilevered portion of an adjacent bridge span during construction.

Massive concrete structural parts of a bridge, also called "cable anchorages" and "shore anchors," these are placed far enough back from the edge of the water to ensure against sliding; they provide stability where the cable end is tied, withstanding the tremendous stress of the loaded cables.

angular motion sensitivity
The ability of an observer to detect changes in the apparent distance and direction of movement of an object as a function of the change in the angular size of the visual stimulus on the observer's retina.

angular velocity threshold
The rate of change in angular size of the visual stimulus that is necessary for an observer to discern that an object's motion has increased or decreased.

annual average daily traffic (AADT)
The total volume passing a point or segment of a highway facility in both directions for one year, divided by the number of days in the year.

The formula share from which one receives funds; example: The state's apportionment grew by 5 percent this year.

A federal budgetary term that refers to a statutorily prescribed division or assignment of funds; it is based on prescribed formulas in the law and consists of dividing authorized obligation authority for a specific program among transit systems.

approach span
The span or spans connecting the bridge abutment with the main span or spans.

A federal budgetary term that refers to an act of Congress that permits federal agencies to incur obligations and make payments out of the treasury for specified purposes; an appropriation act is the most common means of providing budget authority, but in some cases the authorization legislation itself provides the budget authority.

arterial street or highway
A major thoroughfare used primarily for through traffic, rather than access to private land.

articulated bus
An extra-long, high-capacity bus with a rear body section or sections flexibly, but permanently, connected to the forward section; the arrangement allows the vehicle to bend in curves and yet have no interior barrier to movement between the two parts; typically 54 to 60 feet long, an articulated bus has a seating capacity of 60 to 80 passengers.

The surface where the rail and a roadway (or pathway) cross at the same level.

attraction signing
Information/supplemental signs featuring logos or verbal messages pointing out places to visit or food, gas and rest area locations.

Basic, substantive legislation which establishes or continues the legal operation of a federal program or agency, either indefinitely or for a specific period of time, or which sanctions a particular type of obligation or expenditure within a program; an authorization may set appropriation limits.

Legislation assigns a dollar amount that is the maximum amount that can be spent. They can be trust funds or annual funds. Example: The legislative body authorizes the total amount of funds that can be budgeted for the two-year cycle.

Aviation Trust Fund
Fund established by Congress to pay for improvements to the nation's airports and air traffic control system; money in the fund comes solely from users of the system - primarily a tax on domestic airline tickets.

This refers to a contract, not funds. A contract is awarded once the selection process has been completed and a contractor has been chosen.


Flat-bottomed boat designed to carry cargo on inland waterways, usually without engines or crew accommodations; barges can be lashed together and either pushed or pulled by tugs, carrying cargo of 60,000 tons or more; small barges for carrying cargo between ship and shore are known as lighters.

Barnes' Dance timing
Type of exclusive signal timing phase where pedestrians may also cross diagonally, in addition to crossing either street; also referred to as scramble timing.

base fare
The price charged to one adult for one transit ride; excludes transfer charges, zone charges, express service charges, peak period surcharges and reduced fares.

bridge condition index

A linear structural member designed to span from one support to another.

benefit/cost (B/C) ratio
B/C is used to compare the benefit versus the cost of proposed alternatives. For highway projects, benefits may include reduced fuel consumption, travel time and air pollution; costs may include construction, right of way and maintenance.

A substructure unit supporting each end of a bridge span; also called a pier; made up of two or more columns or column-like members connected at their top most ends by a cap, strut or other member holding them in their correct positions.

bicycle facilities
A general term denoting improvements and provisions made to accommodate or encourage bicycling, including parking facilities, all bikeways and shared roadways not specifically designated for bicycle use.

bid and bid process
The process of a public agency requesting proposals for a specific project or scope of work and the response from an individual or firm to secure a contract.

bike lane
A portion of a roadway that has been designated by striping, signing and pavement markings for the preferential or exclusive use of bicyclists.

A bikeway is created when a road has the appropriate design treatment for bicyclists, based on motor vehicle traffic volumes and speeds. On-road bikeways include a shared roadway, shoulder bikeway, bike lane or bicycle boulevard design treatments.

Site for obtaining earth materials for roadway embankment construction.

Highway sections that experience operational problems, such as congestion; bottlenecks may result from factors other than reduced roadway width; for example, the close spacing of exit and entrance ramps can cause weaving patterns that result in congestion; a less obvious example is a steep freeway grade that can slow trucks and cause a localized "bottleneck."

The front of a vessel.

box girder
A support beam that is a hollow box; its cross section is a rectangle or square.

An enclosed car used for general service and especially for lading that must be protected from weather.

brake reaction time
The interval between the instant that the driver recognizes the presence of an object or hazard on the roadway ahead and the driver actually applies the brakes.

branch railroad
Nonclass 1 railroad.

A secondary line of a railroad, not the main line.

budget authority
A federal budgetary term that refers to legal authority given by Congress to federal agencies to make funds available for obligation or expenditure.

budget resolution
A federal budgetary term that refers to a concurrent resolution passed by Congress, but not requiring the signature of the president, setting forth the congressional budget for each of five fiscal years; the budget resolution sets forth various budget total and functional allocations, and may include reconciliation instructions to designated House or Senate committees.

Cargo shipped in loose condition and of a homogeneous nature; cargoes that are shipped unpackaged either dry, such as grain and ore, or liquid, such as petroleum products; bulk service generally is not provided on a regularly scheduled basis, but rather as needed, on specialized ships, transporting a specific commodity.

bulk transfer
The transfer of bulk products, such as plastic pellets or liquid sweeteners, from one mode of transportation to another; bulk transfer permits off-rail shippers and receivers of varied commodities to combine rail's long-haul efficiencies with truck's convenient door-to-door delivery.

A rubber-tired vehicle designed for roadway operation to transport a large number of people for public transportation service.

bus, charter
A bus transporting a group of persons who, pursuant to a common purpose, and under a single contract at a fixed price, have acquired the exclusive use of a bus to travel together under an itinerary.

bus, intercity
A bus with front doors only, high-backed seats, separate luggage compartments, and usually with restroom facilities for use in high-speed, long-distance service.

buttonhook ramp
J-shaped ramp that connects to a parallel or diagonal street or frontage road, which is often well removed from the interchange structure and other ramps.


The part of a suspension bridge or cable-stayed bridge that supports suspension support to the deck; the cable is made of many steel wires bound together into strands and anchored at each end.

cable barrier
A flexible type of traffic barrier consisting of multiple steel cables mounted on steel posts. See also "guardrail."

cable saddle
The cable saddles sit at the summit of each bridge tower. They hold the main suspension cable where it crosses over each tower leg. As traffic, wind and temperature changes affect the movement of the cables, the saddles absorb the load and shift it to the towers.

cable spinning
The technique of pulling wires from the bridge anchorage over towers and back to form the main cable; a "spinning wheel," or "traveler," carriers the wires; at the anchorage the strands of wire are attached to the eye-bar; the wires are grouped into strands then bound tightly together to form strong suspension cables.

cable-stayed bridge
A bridge in which the superstructure is directly supported by cables or stays, passing over or attached to a tower or towers located at the main pier(s).

"Caisson" is the French word for "box." A caisson is a huge box made of steel-reinforced and waterproof concrete with an open central core. At the base of the caisson is its "cutting edge" of plate steel. In a suspension bridge the caisson becomes the foundation, the pier, supporting for the bridge's towers.

The maximum number of vehicles (vehicle capacity) or passengers (person capacity) that can pass over a given section of roadway or transit line in one or both directions during a given period of time under prevailing roadway and traffic conditions.

capital costs
Expenses related to the purchase of tangible property, such as land, buildings and vehicles.

Anything other than passengers, carried for hire, including both mail and freight.

A shipment of not fewer than 5 tons of one commodity.

Formal name for a craft employee that inspects and repairs railway cars.

The movement of a car a distance of one mile; an empty car-mile is a mile run by a freight car without a load; a loaded car-mile is a mile run by a freight car with a load.

Two or more people sharing the use and cost of a privately owned vehicle in traveling to and from prearranged destinations; see also vanpool.

Concrete poured within form at project site to create a structural element in its final position.

Temporary foot bridges, used by bridge workers to spin the main cables (several feet above each catwalk), and attach the suspender cables that connect the main cables to the deck.

The separation or regulation of conflicting traffic movement into definite paths of travel by the use of pavement markings, raised islands or other subtle means, to facilitate the safe and orderly movement of both vehicles and pedestrians.

chevron signs
A chevron symbol (sideways "V") in black, against standard yellow background, on a vertical rectangle; used as an alternate or supplement to standard delineators and to large arrow signs.

A horizontal member of a truss.

Class 1
A railroad having operating revenues of more than $256 million annually.

Clean Air Act (CAA)
The original Clean Air Act was passed in 1963, but our national air pollution control program is actually based on the 1970 version of the law. The 1990 Clean Air Act amendments are the most far-reaching revisions of the 1970 law.

clear zone
Area adjacent to the roadway absent of obstructions or with protected elements.

closed-end street
A street that has only one egress to any other existing street or planned street identified in the local Transportation System Plan; cul-de-sacs, dead-end and looped streets are examples of closed-end streets.

cloverleaf interchange
A form of interchange that provides indirect right-turn movements in all four quadrants by means of loops; generally used where the turning and weaving volumes are relatively low; this type of interchange eliminates all crossing conflicts found in a diamond interchange, but requires more area; the cloverleaf type of interchange can have one or two points of entry and exit on each through roadway.

coal car
A freight car with fixed sides and no roof; for transporting coal.

cold-in-place (CIP) recycling
CIP recycling is an ecofriendly pavement rehabilitation process that uses 2 to 5 inches of the current road surface and pulverizes the material down to a specific aggregate size, and then reuses the material to pave that same road. The process is efficient in saving costs on labor and transportation.

collector/distributor streets
A street that gathers and disperses traffic between larger arterial highways and smaller streets; a collector/distributor street has intersections and provides access to abutting properties.

collector highway
Collector highways are those highways that link local highways to arterial highways.

In rural areas, routes serving intracounty, rather than statewide travel; in urban areas, streets providing direct access to neighborhoods, as well as direct access to arterial.

Commercial and Industrial Network (CIN)
Designated road system of primary highways that connect the state's regional growth areas and carry a significant amount of the state's commercial traffic; the CIN does not include the interstate system.

commercial motor vehicle
Any self-propelled or towed vehicle used on the public highways in commerce to transport passengers or cargo, if the vehicle has a gross weight of 10,000 pounds or more; or is designed to transport more than 15 passengers, including the driver, or is used to transport hazardous materials as defined by law.

commercial service airport
An airport receiving scheduled passenger service and having 2,500 or more enplaned passengers per year.

common carrier
Holds himself out for hire to the public; must post rates and cannot discriminate against customers whose cargo he is equipped to carry.

commuter lane
See high-occupancy vehicle lanes.

commuter rail
Local and regional passenger train operations between a central city, its suburbs and/or another central city; commuter rail usually has only one or two stations in the central business district; it is also known as "suburban rail."

commuter rail transit
Also called regional rail transit, the passenger railroad service carries passengers within urban areas or between urban areas and their suburbs. Commuter rail transit differs from rail rapid transit in a number of ways: heavier passenger cars, longer average trip lengths and passenger stations spaced farther apart.

complete interchange lighting (CIL)
Includes lighting in the interchange area on both the acceleration and deceleration areas, plus the ramps through the terminus.

composite photometry
Light measurement applied to a high-mast lighting system that employs a counter beam arrangement, to take advantage of the efficiency with which pavement luminance can be increased with light directed upstream, while enhancing positive contrast through additively of vehicle headlighting with the light directed downstream.

compressed work week
Also called alternative work hours; alternatives to the Monday through Friday, 8 a.m. to 5 p.m. work schedule; a compressed work week allows employees to work longer days and report to the work site less often.

concrete safety shaped barrier (CSSB)
Commonly used median barrier where there is heavy vehicle travel and narrow medians.

Highway congestion results when traffic demand approaches or exceeds the available capacity of the transportation facility(ies).

Congestion Mitigation and Air Quality Improvement Program (CMAQ)
This federal funding source supports programs and projects to improve air quality.

connecting carrier
Railroad with a physical connection to another.

constant warning time (CWT)
Circuitry at active warning devices that provides a constant warning time, despite the speed at which a train is approaching.

A detailed review of construction issues and sequencing of a project during the project development phase.

continuously operating reference station (CORS)
Surveyors, geographical information system users, engineers, scientists and the public that collect GPS data can use CORS data to improve the precision of their positions.

contract authority
A federal budgetary term that refers to a form of budget authority permitting obligations to be incurred in advance of appropriations; advance obligations, however, have been limited by the appropriations committees with obligation limitations.

See luminance contrast.

contrast sensitivity
Ability to perceive a lightness or brightness difference between two areas; frequently measured for a range of target patterns differing in value along some dimension, such as pattern element size and portrayed graphically in a contrast sensitivity function in which the reciprocal of contrast threshold is plotted against pattern spatial frequency or against visual angle subtended at the eye by pattern elements.

controlled access
Partial access restriction that gives preference to through traffic; also provides for connections to selected public routes and to certain other adjacent locations where vehicles can enter or leave a roadway safely without interfering with through traffic.

A broad geographical band that follows the general directional flow or connects major sources and destinations or trips; generally representing the major travel patterns within a region, corridors may contain a number of streets, highways and transit route alignments.

County-State Traffic Engineering Program (C-STEP)
A traffic safety improvement program funded 45 percent by the county and 55 percent by the state on the rural portion of the primary road system.

crash rate
Measure of the number of crashes on a roadway segment related to the amount of traffic on that segment; the rate is calculated by taking the number of crashes over a given time period divided by the total vehicle-miles of travel on a roadway segment; the rate is typically reported in number of crashes per hundred million vehicle-miles of travel.

critical gap
The gap (distance to nearest vehicle) in oncoming or cross traffic that a driver will accept to initiate a turning or crossing maneuver 50 percent of the time it is presented, typically measured in seconds.

cross brace
Transverse brace between two main longitudinal members.

Commonly used by railroads, a crossarm, located at the top of a utility pole, is a wooden bar to which power lines are attached; the crossarm keeps the lines separated by a sufficient distance to prevent arcing.

Crossbucks are white reflectorized X-shaped signs with "RAILROAD CROSSING" in black lettering, located alongside the roadway at railroad tracks. A crossbuck is to be viewed as a yield sign, and is a regulatory sign.

Two track switches laid back-to-back to allow trains to move from one track to another parallel track.

cross section
A section formed by a plane cutting through an object, usually at right angles to an axis.

A point along a street that is identified by striping, signage and/or signal lights that designate it as a spot for pedestrians to cross the street.


The action of reducing the vibration of an object; this tends to return the vibrating object to its original position.

dark adaptation
Adjustment of the eye to low levels of illumination, which results in increased sensitivity to light.

dead load
A static load due to the weight of the structure itself.

The movement of a transit vehicle without fare-paying passengers aboard, often to and from a garage or terminal or between routes, also refers to commercial truck movement when the unit is moving empty cargo.

deceleration lane
A lane designed to allow traffic to safely decrease speed.

decision sight distance (DSD)
The distance required for a driver to detect an unexpected or otherwise difficult-to-perceive information source or hazard in a roadway environment that may be visually cluttered, recognize the hazard or its threat potential, select an appropriate speed and path, and initiate and complete the required safety maneuver safely and efficiently.

The roadway portion of a bridge that directly supports vehicular and pedestrian traffic.

deck bridge
A bridge in which the supporting members are all beneath the roadway.

deck truss
A bridge whose roadway is supported from beneath by a truss.

depth perception
The ability to distinguish the relative distance of objects in visual space, used to interpret their motion over multiple observations.

design criteria
Established state and national standards and procedures that guide the establishment of roadway layouts, alignments, geometry and dimensions for specified types of roadways in certain defined conditions; the principal design criteria for roadways are traffic volume, design speed, the physical characteristics of vehicles, the classification of vehicles and the percentage of various vehicle classification types that use the roadway.

A sloping structural member of a truss or bracing system.

diamond interchange
The simplest and perhaps most common type of interchange; this type of interchange contains a one-way, diamond-type ramp in one or more of the quadrants; the diamond interchange provides for all movements to and from the intersecting road.

disadvantaged business enterprise (DBE)
A business owned and operated by one or more socially and economically disadvantaged individuals; socially and economically disadvantaged individuals include African Americans, Hispanic Americans, Native Americans, Asian Pacific Americans or Asian Indian Americans, and any other minorities or individuals found to be disadvantaged by the Small Business Administration under Section 8(a) of the Small Business Act.

discretionary spending
A federal budgetary term that refers to any funds whose distribution is not automatic; discretionary spending encompasses programs controlled by annual appropriations bills and is subject to the constraints imposed by the discretionary spending limits set in the balanced budget law.

diverge steering zone
Used with interchange/ramp exit models; it is the distance upstream from the exit gore at which a driver begins to diverge from the freeway.

divided attention
The ability of a driver to allocate attention among tasks or stimuli in the roadway environment, where more than one task or stimulus is perceived to be important to safe performance at a given time.

divided highway
Roadway that is separated by a median.

Shipping containers that can be stacked atop one another on a railroad flatcar.

drawn down
Using funds that have been awarded.

dynamic message sign (DMS)
An electronic traffic sign is often used on roadways to give travelers information about special events; they warn of traffic congestion, accidents, incidents, roadwork zones or speed limits on a specific highway segment; they may also ask vehicles to take alternative routes, limit travel speed, warn of duration and location of the incidents, or just inform of the traffic conditions.

dynamic visual acuity
Acuteness or clarity of vision for an object that has angular movement relative to the observer; acuity depends on sharpness of retinal focus, sensitivity of nervous elements, oculomotor coordination, interpretive faculty of the brain and contextual variables.


A federal budgetary term that refers to the specific designation by Congress that is part of a more general lump-sum appropriation to be used for a particular project; the earmark can be designated as a minimum and/or maximum dollar amount.

edgeline visibility
The detection/recognition of painted pavement surface delineation along roadway edges.

The point at which there is a complete contract, used in various terms; encumbered is one type of obligation.

Passenger boardings at airports.

environmental assessment (EA)
Compared to an environmental impact statement, an environmental assessment is a less-detailed level of environmental scrutiny. At the conclusion of the environmental assessment, an environmental impact statement may be ordered if conditions warrant. If not, a finding of no significant impact (FONSI) will be issued.

environmental impact statement (EIS)
One of the environmental protection mechanisms established by the National Environmental Policy Act of 1969; environmental impact statements report the environmental impacts that will likely result from major federally assisted projects.

Environmental Protection Agency (EPA)
The federal department that oversees enforcement of major environmental laws.

environmental stewardship
A philosophical concept of government, the public, resource users and businesses all taking responsibility and working together to care for natural resources.

essential air service
Government subsidized airline service to rural areas of the United States that continued after the Airline Deregulation Act of 1978.

exit gore area
The area located immediately between the left edge of a ramp pavement and right edge of the mainline roadway pavement at a merge or diverge area.

expansion joint
A joint in concrete paving or bridge construction designed to provide means for expansion and contraction movements produced by temperature changes, load or other forces.

Same as drawn down, but uses its own funds.

An expressway is a divided highway facility usually having two or more lanes for the exclusive use of traffic in each direction and partial control of access; as opposed to a freeway that has full control of access.

Steel bars that hold wire strands of the main bridge cable and are attached to beams embedded in the concrete of an anchorage.


fare box revenue
Value of cash, tickets, tokens and pass receipts given by passengers as payment for rides; excludes charter revenue.

An identifier for a roadway designated by the Iowa Transportation Commission to be part of the statewide highway system; normally associated as a two-lane roadway in rural areas, but are located in urban areas and can be a four- or six-lane divided roadway.

fatality rate
The number of fatalities per 100 million vehicle-miles traveled.

Cause of structural deficiencies, usually due to repetitive loading over time; also refers to tired drivers.

feasibility study
A study about a project's feasibility that is summarized in a document; the study addresses issues, including the project's benefits, costs, effectiveness, alternatives considered, analysis of alternative selections, environmental effects, public opinions and other factors; the feasibility study for major projects involving federal funds was replaced under the Intermodal Surface Transportation Efficiency Act by the Major Investment Study.

federal-aid highway(s)
Those highways eligible for assistance under Title 23 of the United States Code, which does not include those functionally classified as local or rural minor collectors.

federal-aid project
An activity, study, survey, project or other work related to transportation authorized in advance by the Federal Highway Administration, Federal Transit Administration or other federal agency and that is paid for either partially or fully by public funds.

Federal Aviation Administration (FAA)
The government agency responsible for air safety and operation of the air traffic control system, the FAA also administers a program that provides grants from the Airport and Airway Trust Fund for airport development.

federal fiscal year (FFY)
The yearly accounting period for the federal government which begins Oct. 1 and ends on the following Sept. 30; the fiscal year is designated by the calendar year in which it ends (e.g., FY 06 is from Oct. 1, 2005, to Sept. 30, 2006).

finding of no significant impact (FONSI)
Issued at the conclusion of an environmental assessment when the determination has been made that an environmental impact statement is not necessary for a specified project.

fixed cost
An indirect cost that remains relatively constant, irrespective of the level of operational activity.

fixed-route transit
A system of transit vehicles that follows a schedule over one or more prescribed routes.

The person assigned to duties at the rear of the train, primarily responsible for applying the breaks; roadway work zone.

An open railroad car without sides or a roof.

Work system allowing alternative work hours to the standard 8 a.m. – 5 p.m., with no change in length of shift.

The enlarged, lower portion of a substructure that distributes the structure load either to the earth or to supporting piles; the most common footing is the concrete slab; "footer" is a colloquial term for footing.

formula funds
Funds distributed or apportioned to qualifying recipients on the basis of formulas described in law.

A divided highway facility having two or more lanes for the exclusive use of traffic in each direction and full control of access; the freeway is the only type of highway intended to provide complete "uninterrupted" flow.

freight intermodal facility
An intercity facility where freight is transferred between two or more modes (e.g., truck to rail, rail to ship, truck to air, etc.).

frontage road
An arterial type roadway that parallels a major transportation facility, such as a freeway; it serves to collect and distribute traffic along the major facility without impeding flow along the freeway; frontage roads are also referred to by the public as "access," "feeder" and "service" roads.

full-diamond interchange
Interchange with a one-way, diagonal-type ramp in each quadrant.

functional roadway classification
The organization of roadways into a hierarchy based on the character of service provided; typical classifications include arterial, local and collection roadways.


gap acceptance
The decision by a driver that there is sufficient time and/or distance ahead of an approaching vehicle to allow safe performance of a desired crossing or merging maneuver.

gap judgments
The judgment of a driver of the time and/or distance ahead of an approaching vehicle traveling in a lane that the driver wishes to turn across or merge into.

gap search and acceptance (GSA) zone
Used with interchange/ramp entry traffic models, it is the zone in which the driver searches, evaluates and accepts or rejects the available lags or gaps in the traffic stream for execution of a merging maneuver.

General Accountability Office (GAO)
Conducts analysis of federal programs.

general aviation airport
An airport that serves corporate aviation, flight schools, air charter operations, light cargo or private pilots flying for business or recreation.

A main support member for the bridge structure that usually receives loads from floor beams and stringers; also, any large beam, especially if built up.

geographic information system (GIS)
Computerized mapping and planning tool.

global positioning system (GPS)
A navigation system that uses satellites to provide a receiver on earth with extremely accurate measurements of its three-dimensional position, velocity and time.

The slope (ratio of change in elevation to change in distance) of a roadway typically given in percent; for example, a 2 percent grade represents 2 feet of elevation change over a 100-foot distance.

grade crossing
The point at which a roadway intersects a rail line.

"Green Book"
The official title of this book is: "A Policy on Geometric Design of Highways and Streets." This book is published by AASHTO and contains accepted practices for designing the physical features of a roadway. Examples of these features are sight distance, design speeds, lane width, horizontal and vertical curves, etc.

gross ton-mile
The movement of the combined weight of railroad cars and their contents a distance of one mile.

gross tonnage
The overall volume of a ship's hull, including crew cabins, storerooms and machinery spaces; a ton equals 100 cubic feet.

Protective barrier along a roadway to prevent vehicles from leaving the roadway or crossing the centerline.


half-diamond interchange
An interchange with a one-way, diagonal-type ramp in two adjacent quadrants; this type of interchange is appropriate to situations in which traffic demand is predominantly in one direction.

A tension member serving to suspend an attached member on a bridge.
A facility where airplanes are stored.

haulage rights
Rights obtained by one railroad to have its trains operated by another railroad over that railroad's tracks.

high-occupancy vehicle (HOV)
Any passenger vehicle that meets or exceeds a certain, predetermined minimum of passengers, generally two or more.

high-occupancy vehicle lane
A highway or street lane reserved for one or more specified category of vehicle, usually buses, carpools and vanpools.

high-mast lighting
Illumination of a large area by means of a cluster of luminaries, which are designed to be mounted in fixed orientation at the top of a high mast (generally 80 feet or higher).

high-spatial-frequency stimulus
A visual target characterized by fine detail.

highway advisory radio (HAR)
A radio station which broadcasts highway conditions and traffic information.

The point at which a roadway and railway intersect.

highway sufficiency rating
A 0-100 rating representing the relative condition of the highway segment (0 worst – 100 best); this measure takes into account the structural adequacy, safety and service of each segment; the rating is used as a performance measure and as a tool to identify reconstruction needs; per Code of Iowa requirements, department staff calculates ratings annually for all state highway segments.

Highway Trust Fund
The federal trust fund established by the Highway Revenue Act of 1956; this fund has two accounts — the Highway Account and the Mass Transit Account; trust fund revenues are derived from federal highway-user taxes and fees such as motor fuel taxes; trust fund uses and expenditures are determined by law.

A point in a structure at which a member is free to rotate.

An open-top railroad car with pockets or hoppers, opening on the underside of the railcar for unloading bulk commodities.

horizontal alignment
The linear (tangent) character or specific degree of curvature describing the geometry of a defined section of highway in plain view.


The density of luminous flux (rate of emission of luminous energy flow of a light source in all directions) incident on a surface; the quotient of the flux divided by the area of the surface, when the surface is uniformly illuminated.

The amount of light falling onto a surface.

An incident may be any of the following: traffic accident, stalled vehicle, load spillage or other action that affects one or more lanes of traffic; an "accident" typically involves a collision of a moving vehicle with another vehicle, person or object.

initial acceleration (IA) zone
Used with interchange/ramp entry traffic models, it is the zone in which the driver accelerates to reduce the speed differential between the ramp vehicle and the freeway vehicle to an acceptable level for completing the merge process.

in-service brightness level (ISBL)
The brightness level of a delineation treatment at an intermediate point in its anticipated service life; this value varies by type of delineator, type of wear (traffic level) and environmental conditions.

intelligent transportation system (ITS)
ITS is a surveillance system designed to monitor traffic flows on major freeways and to inform motorists of problem areas. Some ITS technology includes changeable message signs (CMS), cameras, and video detectors. ITS applications include the integration of traffic control and transportation management systems; traffic signals which adapt to traffic and change control each cycle; highway advisory radio systems; CMS; vehicle detectors; closed-circuit television; global positioning systems and route guidance (currently used in some trucks, buses and rental cars). An ITS may enable drivers to operate their vehicles more safely and with greater knowledge about existing traffic conditions.

interchange (grade separation)
A system of interconnecting roadways that provides for the movement of traffic between two or more highways on different levels.

Switching from one form of transportation to another.

intermodal facility
A transportation element that accommodates and interconnects different modes of transportation and services the statewide, interstate and international movement of people or goods. For example, an intermodal yard is a railyard that facilitates the transfer of containers or trailers to a commercial motor carrier.

intermodal service
Freight moving via at least two different modes of transport; intermodal service generally involves the shipment of containers and trailers by rail, truck, barge or ship.

International Registration Plan (IRP)
IRP is a method of registering fleets of vehicles that travel in two or more member jurisdictions. Motor carriers that qualify for IRP must register fleets of vehicles in their home or “base” jurisdiction. A fleet, for IRP purposes, is comprised of one or more vehicles that pay registration fees in multiple states.

intersecting angle (skew)
The angle formed by the intersection of two roadways (other than a 90-degree angle).

intersection sight distance (ISD)
The unobstructed view of an entire (at-grade) intersection and sufficient lengths of the intersecting highway to permit control of the vehicle to avoid collisions during through and turning movements.

Interstate Highway System
A network of freeways in the United States; the Interstate Highway System is a separate system within the larger National Highway System; the entire system, as of October 2002, had a total length of 46,726 miles.

Iowa in Motion
The process used by the department to develop the State Transportation Plan (STP) that was adopted by the Commission on July 15, 1997; the plan is intended to guide the development of transportation policies, goals, objectives, initiatives and investment decisions through the year 2020.

Iowa Plane Coordinate System
Iowa's geographical coordinate system.

Iowa Statewide Transportation Improvement Program (STIP)
A two-year program of transportation projects required by SAFETEA-LU, consisting of a federally required document that allocates transportation funds to a staged, multiyear, statewide, intermodal program of transportation projects; consistent with the statewide transportation plan and planning processes and metropolitan plans, TIPs and processes; the metropolitan TIP must be included in the STIP without change.


Job Access Reverse Commute (JARC) program
A federal program that provides grants to help states and localities develop a coordinated regional approach to new or expanded transportation services that connect welfare recipients and other low-income persons to jobs and other employment services.

In stone masonry, the space between individual stone; in concrete, a division in continuity of the concrete; in a truss, the point at which members of a truss frame are joined.



The product of centerline-miles and number of lanes. Example: A four-lane road, 2 miles long, has eight lane-miles.

Legibility Index (LI)
Used to describe the relative legibility of different letter styles; it is calculated from the distance at which a character, word or message is legible divided by the size of the letters on the sign.

less-than-truckload (LTL)
The quantity of freight that is less than that is required for application of a trailer load rate.

The process by which the Iowa DOT requests and decides on bids from competing companies for work on transportation projects.

level of service
A description of the quality of service that can be expected by users of transportation facilities.

level of service (LOS)
A qualitative measure describing operational conditions within a traffic stream, based upon service measures, such as speed and travel time, freedom to maneuver, traffic interruptions, comfort and convenience; LOS A represents completely free flow of traffic allowing traffic to maneuver unimpeded; LOS F represents a complete breakdown in traffic flow resulting in stop and go travel; LOS is typically calculated based upon peak-hour conditions.

light rail transit
A type of electric rail system with a "light" total passenger carrying capacity compared to the capacity of heavy rail transit.

limited access highway
Highway designated for through traffic with very few entrances and exits.

limited sight distance
A restricted preview of the traveled way downstream due to a crest vertical curvature or horizontal curvature of the roadway, or to blockage or obstruction by a natural or constructed roadway feature or by (an)other vehicle(s).

line capacity
The maximum number of trains that can operate safely and reliably over a given segment of track during a given period of time.

line-haul service
The movement over the tracks of a carrier from one city to another, not including the switching service.

liquefied natural gas (LNG)
An alternative fuel; a natural gas cooled to below its boiling point of -260 degrees Fahrenheit so that it becomes a liquid; stored in a vacuum bottle-type container at very low temperatures and under moderate pressure; LNG vapor is lighter than air.

longer combination vehicles (LCV)
Commercial motor vehicles with two or more trailers.

lower chord
The bottom horizontal member of a truss.

A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and to connect the lamps to the power supply.

The luminous intensity or brightness of any surface in a given direction, per unit of projected area of the surface as viewed from that direction, independent of viewing distance; the International System of Units is the candela per square meter.

luminance contrast
The difference between the luminance of a target area and a surrounding background area, divided by the background luminance alone (e.g., lane marking minus lane pavement surface, divided by pavement surface).


machine control grading
Also called machine guidance.

main beam
A beam supporting the bridge spans and bearing directly onto a column or wall.

main line
Primary rail line over which trains operate between terminals; it excludes sidings, and yard and industry tracks.

main track
A railroad's primary track that usually extends great distances, it usually carries both freight and passenger trains.

The maintenance of railroad rights of way, it can include procedures from the initial grading of the right of way to its general upkeep and eventual dismantling.

major air carrier
An airline with annual revenue of more than $1 billion.

Manual on Uniform Traffic Control Devices (MUTCD)
This manual is published by the Federal Highway Administration and used by most departments of transportation across the country as the standard for traffic control devices. These devices include signals, signs and pavement striping.

Moving Ahead for Progress in the 21st Century (MAP-21)
Passed on June 29, 2012; signed on July 6, 2012 (Pub. L. 112-141)

marked pedestrian crossing
Any portion of a roadway at an intersection or elsewhere that is distinctly indicated for pedestrian crossing by lines or other markings on the surface of the roadway.

Mass Transit Account
The federal account, established by the Surface Transportation Assistance Act of 1982, into which a designated portion of the federal Highway Trust Fund revenue from motor fuel taxes is placed (1.5 cents in 1994); this account is used for federal mass transportation assistance.

mass transportation
Transportation by bus, rail, boat or other conveyance, either publicly or privately owned, that provides general or special service to the public on a regular and continuing basis (not including school bus, charter or sight-seeing service).

measures of effectiveness (MOEs)
Descriptions of driver or traffic behaviors that quantify the level of safety or service provided by facility or treatment to drivers, passengers or pedestrians; examples include vehicle speed, trajectory, delay and similar measures; MOEs are the dependent measures (e.g., the effects/behaviors resulting from introduction of a treatment or countermeasure).

An island in the center of a street or intersection to protect pedestrians and provide landscaping; medians prevent passing and left turns, separate opposing travel lanes, and provide visual enhancement.

median barriers
A longitudinal system of physical barriers used to prevent an errant vehicle from crossing the portion of the divided highway separating traffic moving in opposite directions.

An individual angle, beam, plate or built piece intended to become an integral part of an assembled frame or structure.

merge steering control (MSC) zone
Used with interchange/ramp entry traffic models, it is the zone in which the driver enters the freeway and positions the vehicle in the nearest lane on the mainline.

metropolitan planning organization (MPO)
The organization designated by local elected officials to be responsible for carrying out the region transportation planning process and other regional planning processes; the MPO must be in place in every urbanized area with a population greater than 50,000; the MPO's responsibilities include the 20-year long-range plan and transportation improvement program.

Metropolitan Transportation Improvement Program (MTIP)
A staged, multiyear, intermodal program of transportation projects that is consistent with the metropolitan transportation plan.

A thin surface treatment (about ½ inch thick) used as a preventive maintenance tool to extend pavement life. It provides a new roadway wearing surface that helps to slow pavement deterioration caused by water and the environment. It also can correct minor surface profile irregularities.

A green paddle-shaped sign alongside roads and highways that indicates the total mileage from a certain control point; for Interstate routes, the zero milepost is generally at the southern or western end of the route; for all other routes, the location of the zero milepost may vary.

minimum required visibility distance (MRVD)
The distance necessary to permit detection and comprehension, plus driver decision making, response selection and completion of vehicle maneuver, if necessary.

minority business enterprise (MBE)
A business owned and operated by one or more individuals who are defined as minorities under U.S. Department of Transportation regulations; see also "disadvantaged business enterprise"

mitigation measures
Specific design commitments made during the environmental evaluation and study process that serve to moderate or lessen impacts deriving from the proposed action; these measures may include planning and development commitments, environmental measures, right-of-way improvements, and agreements with resource or other agencies to effect construction or post construction action.

The ability to move people and goods from place to place, or the potential for movement, mobility improves when the transportation network is refined or expanded to improve capacity of one or more modes, thus, allowing people and goods to move more quickly toward a particular destination.

A general term to describe a manner of transportation; walking, driving, taking a bus or train or bicycling are all modes of transportation.

multilevel car
A long railroad flatcar designed with one or more deck levels in addition to the car's main deck; used to haul new automobiles and trucks.

Concerning or involving more than one transportation mode.


national air carrier
An airline with annual revenues of between $100 million and $1 billion.

National Environmental Policy Act (NEPA)
Federal law providing for environmental assessments of impacts and public input into all federally funded projects; an environmental study could be either an environmental impact statement or environmental assessment.

National Highway System (NHS)
An approximately 155,000-mile, still-to-be-designated network, to provide an interconnected system of principal routes to serve major travel destinations and population centers; picks up where the Interstate Highway System left off.

no-build alternative (also known as “no-action alternative”)
Option of maintaining the status quo by not building transportation improvements; serves as a baseline for comparison of “build” alternatives.

North American Free Trade Agreement (NAFTA)
A formal agreement, or treaty, between Canada, Mexico and the United States of America to promote means for improved and increased free trade between the three countries; the effect of NAFTA on transportation was to increase the need to upgrade existing, and build new, transportation facilities between and within the countries.

no turn on red (NTOR)
This message on signs is used to indicate that a right turn on red (or left turn on red for one-way streets) is not permitted at an intersection.

notice of intent (NOI)
A notice that is prepared to inform the public that an environmental impact statement will be prepared for a project.

nonattainment area
A metropolitan area that has failed to meet national ambient air quality standards.


The money for a project becomes "obligated" once the moneys have gone from the "promise" to actually being in an account.

A federal budgetary term that refers to a binding agreement that will result in an outlay; an agreement by the federal government to pay for goods or services immediately or at some future time when the goods or services are delivered; also known as a "commitment."

obligation limitation
A federal budgetary term that refers to a limit placed in appropriations bills on the amount of federal assistance that may be obligated during a specified time period; it does not affect the scheduled apportionment or allocation of funds; it just controls the rate at which these funds may be used.

Those periods of time outside the morning and afternoon peak travel periods, the nonrush hour periods when travel activity tends to be lower.

operating assistance
Financial assistance for transit operating expenses (not capital costs); such aid may originate with federal, local or state governments.

operating deficit
The sum of all operating expenses minus operating revenues.

operating expense
Moneys paid in salaries, wages, materials, supplies and equipment in order to maintain equipment and buildings, operate vehicles, rent equipment and facilities, and settle claims.

operating ratio
The percentage of revenues that goes into operating the railroad; it is calculated by dividing railway operating expenses by railway operating revenues.

operating revenue
Moneys used to fund general, day-to-day costs of running transportation systems; for transit, costs include fuel, salaries and replacement parts; for roads, operating costs involve maintaining pavement, filling potholes, paying workers' salaries, and so forth.

A periodic movement back and forth between two extreme limits; an example is the string of a guitar that has been plucked; its vibration back and forth is one oscillation; a vibration is described by its size (amplitude), its oscillation rate (frequency), and its timing (phase); in a suspension bridge, oscillation results from energy collected and stored by the bridge; if a part of the bridge has to store more energy than it is capable of storing, that part will probably fail.

A federal budgetary term that refers to a payment made to meet an obligation; the point at which an actual payment of money is made.


The portion of a truss span between adjacent points of intersection of bridge web and chord members.

Comparable transportation service required by the Americans with Disabilities Act (ADA) of 1990 for individuals with disabilities who are unable to use fixed-route transportation systems.

parclo loop ramp
A (partial cloverleaf) interchange with loops in advance of the minor road with direction of travel on the freeway; and in the same interchange area, an interchange with loops beyond the minor road.

A mode of travel, usually associated with movements between work and home that involve use of a private auto on one portion of the trip and a transit vehicle (i.e., a bus or a light-rail vehicle) on another portion of the trip.

partial interchange lighting (PIL)
Lighting on an interchange that consists of a few luminaries located in the general areas where entrance and exit ramps connect with the through traffic lanes of a freeway (between the entry gore and the end of the acceleration ramp or exit gore and the beginning of the deceleration ramp).

passenger facility charge
A tax authorized by Congress, approved by the Federal Aviation Administration, assessed by airports, and collected by airlines as an add-on to the passenger airfare; it is designated to help pay for airport improvements that enhance safety and capacity and is not revenue for airlines.

passenger miles
The total number of miles traveled by passengers on transit or railroad vehicles.

Unit of measure that is a product of average trip length multiplied by number of passengers; statistics for transportation safety, for example, are cited on the basis of passenger miles.

passive warning device
Signs or markers used at all highway-rail grade crossings.

Pavement Condition Index (PCI)
A 0-100 rating representing the condition of state highway pavements (0 worst – 100 best); PCI is a measure of pavement condition only and does not consider geometrics, safety or congestion; the index is used as a network-level performance measure and as one of many tools to identify pavement improvement needs.

peak intensity
The maximum strength of a traffic signal maintained through a defined viewing angle; measured in candelas.

A person on foot, in a wheelchair or walking a bicycle.

pedestrian control device
A special type of device (including pedestrian signal indications and sign panels) intended for the exclusive purpose of controlling pedestrian traffic in crosswalks.

pedestrian facility
A facility provided for the benefit of pedestrian travel, including walkways, crosswalks, signs, signals, illumination and benches.

perception-reaction time (PRT)
The interval between a driver's detection of a target stimulus or event and the initiation of a vehicle control movement in response to the stimulus or event.

A vertical support or substructure unit that supports the spans of a multispan superstructure at an intermediate location between its abutments.

A shaft-like linear member that carries loads through weak layers of soil to those capable of supporting such loads.

pile bent
A row of driven or placed piles with a pile cap to hold them in their correct positions; see bent.

plate girder
A large solid web plate with flange plates attached to the web plate by flange angles or fillet welds.

The clear, unobstructed space of a bridge forming the entrance to the structure.

positive offset
A term used to describe the alignment of opposing left-turn lanes at an intersection; this geometry exists when the left boundary of one left-turn lane, when extended across the intersection, falls to the right of the right boundary of the opposite left-turn lane.

posted speed
This term refers to the posted speed limit on a given street or the legal speed limit as defined.

post-mounted delineators (PMDs)
Retroreflective devices located serially at the side of a roadway to indicate alignment; each delineator consists of a flat reflecting surface, typically a vertical rectangle, mounted on a supporting post.

preliminary design
An engineering design that specifies in detail the location and alignment of a planned transportation facility or improvement.

Primary Highway System
Highways that have been functionally classified by the Iowa Department of Transportation as either principal or minor arterials, and that have been selected by the Iowa Transportation Commission to be placed on the Primary Highway System.

A general term to refer to a series of activities carried out by planners, including data assessment, appraisal of identified planning needs, and consideration of available or anticipated fiscal resources to result in the drawing up, scheduling, and planning of a list of identified transportation improvements for a given period of time.

public hearing
A NEPA required meeting designed to afford the public the latest project information and the opportunity to express support of or opposition to a transportation project in a forum at which a verbatim record (transcript) of the proceedings is kept.

public meeting
An announced meeting conducted by transportation officials designed to facilitate participation in the decision-making process and to assist the public in gaining an informed view of a proposed project at any level of the transportation project development process; also, such a gathering may be referred to as a public information meeting.

public service announcement (PSA)
Television and/or radio messages.

public transportation
Services provided for the public on a regular basis by vehicles such as a bus or rail on public ways, using specified routes and schedules; usually on a fare-paying basis; also includes nonscheduled, on-demand transit services.



A railroad car.

rail, high speed
A rail transportation system with exclusive right of way that serves densely traveled corridors at speeds of 124 mph (200 km/h) and greater.

rail main line
A principal or well established rail line (Class I rail lines; e.g., Union Pacific and BNSF Railroad).

rail rapid transit
A system operating high-speed, high-capacity passenger trains using an exclusive, fixed right of way.

railway, railroad
A road composed of parallel steel rails supported by ties and providing a track for locomotive-drawn trains or other wheeled vehicles.

raised pavement markers (RPMs)
Used as positioning guides and/or as supplements or substitutes for other types of markings; these markers conform to the color of the marking for which they serve as a positioning guide, can be mono- or bidirectional and are fastened into the pavement with the reflector surface visible above the road surface.

reaction time (RT)
The time from the onset of a stimulus to the beginning of a driver's (or pedestrian's) response to the stimulus, by a simple movement of a limb or other body part.

real-time kinematic global positioning system (RTK-GPS)
This is a satellite navigation technique used in land and hydrographic survey.

reasonably direct
Either a route that does not deviate unnecessarily from a straight line or a route that does not involve a significant amount of out-of-direction travel for likely users.

record of decision (ROD)
The final approval of an environmental impact statement issued by the Federal Highway Administration.

regional transportation needs
Needs for movement of people and goods between and through communities and accessibility to regional destinations within a metropolitan area, county or associated group of counties.

Regional Transportation Plan (RTP)
The official intermodal transportation plan that is developed and adopted through the metropolitan transportation planning process for the metropolitan planning area.

Paid back; in some cases, municipalities must first spend the money before getting funds back from the state.

reinforced concrete
Concrete with steel reinforcing bars bonded within it to supply increased tensile strength and durability.

A federal budgetary term that refers to the cancellation, in whole or part, of budget authority previously granted by Congress.

The regular vibration of an object as it responds in step (at the same frequency) with an external force.

resurfacing program
Provides for pavement resurfacing, rehabilitation, minor reconstruction, and pavement milling and recycling; such projects are intended to preserve the structural integrity of highway pavements.

reverse commuting
Movement in a direction opposite the main flow of traffic, such as from the central city to a suburb during the morning peak period.

The number of people making one-way trips on a public transportation system in a given time period.

The shared use of a vehicle, such as a van or an automobile, to make a trip.

right of way and right-of-way
Right of way
The land (usually a strip) acquired for or devoted to transportation purposes. For example, highway ROW and railroad ROW.

Right-of-way (hyphenated if an adjective, e.g., right-of-way agreement)
A general term denoting land or property acquired for or devoted to transportation purposes, but with other associated uses such as utilities, water and sewage lines and buffer zones.

right turn on red (RTOR)
Unless otherwise specified by traffic control signage, this practice permits a driver to proceed with a right turn on red signal after stopping at signalized intersections. It provides increased capacity and operational efficiency at a low cost.

rigid frame bridge
A bridge with moment-resistant connections between the superstructure and substructure to produce an integral, elastic structure.

riveted connection
A rigid connection of metal bridge members that is assembled with rivets; riveted connections increase the strength of the structure.

Railroad employee in charge of track maintenance.

Roadway Asset Management System (RAMS)
An interface for accessing datasets that is an internet-based, mobile-friendly web environment.

rolling stock
The vehicles used in a transit system, including buses and rail cars.

A type of road junction (or traffic calming device) at which traffic streams around a central island, after first yielding (giving way) to the circulating traffic.

The sum of the lengths of all the routes in a transit network less any miles duplicated among them.

rumble strips
Driver aids placed in the edges of a roadway pavement.


Safe Routes to School (SRTS) [program]
A federally funded grant program intended to increase the number of children safely walking and bicycling to and from school. Projects include infrastructure improvements (sidewalks, traffic signals, pavement markings, etc.) and noninfrastructure activities (education and encouragement programs).

SAFETEA-LU (Safe, Accountable, Flexible, Efficient Transportation Equity Act:
A Legacy for Users)
The federal surface transportation legislation (Public Law 109-59) that authorizes programs for highways, highway safety and transit for the five-year period 2005-2009.

safety hangers
Backup for original bridge or structural connections to provide redundancy; often added for seismic retrofit.

Safety Management System
A systematic process that has the goal of reducing the number and severity of traffic crashes by ensuring that all opportunities to improve highway safety are identified, considered, implemented as appropriate and evaluated in all phases of highway planning, design, construction, maintenance and operation; and by providing information for selecting and implementing effective highway safety strategies and projects.

scissors off-ramp
A condition where one-way traffic streams cross by merging and diverging maneuvers onto exit ramps; drivers tend to go straight ahead onto an off-ramp instead of turning left.

Secondary Roadway System
Noninterstate roads.

selective attention
The ability, on an ongoing moment-to-moment basis while driving, to identify and allocate attention to the most relevant information, especially embedded when within a visually complex scene and in the presence of a number of distracters.

shared roadway
A type of roadway where bicyclists and motor vehicles share a travel lane.

short line
An independent railroad company that operates over a relatively short distance.

sight distance
The length of highway visible to the driver.

sight triangle
In plain view, the area defined by the point of intersection of two roadways, and by the driver's line of sight from the point of approach along one leg of the intersection, to the farthest unobstructed location on another leg of the intersection.

single-occupancy vehicle (SOV)
This term refers to vehicles that are carrying one person.

situational awareness
The selective attention to and perception of environmental elements within a specified space and time envelope, the comprehension of their meaning and projection of their status in the near future.

slip ramp
A diagonal ramp, more properly called a cross connection, which connects with a parallel frontage road.

small target visibility (STV)
A proposed criterion for roadway lighting; the concept assumes that increased target visibility results in both increased nighttime safety and improved nighttime driver performance; a surrogate for reduced accident risk.

A general term used to describe irritating haze produced by photochemical reactions in the atmosphere.

The distance between bridge piers, towers or abutments.

special mobile equipment (SME)
Off-highway equipment incidentally operated on highways.

Design speed is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern. The design speed of a roadway dictates which geometric design standards are used such as stopping sight distance, radius of curves, and banking (superelevation) of road surfaces.

Operating speed is the speed at which drivers are observed operating their vehicles.

Posted speed is the maximum speed limit posted on a section of roadway using a regulatory sign.

speed-change lane (SCL)
Used in the interchange/ramp exit models; it refers to the speed-change maneuver on deceleration lanes segmented components.

A haphazard and disorderly form of urban development; there are several elements that characterize a sprawl.

Able to resist forces that can cause material deformation or structural collapse.

Statewide Transportation Improvement Program, Iowa (STIP)
A two-year program of transportation projects required by SAFETEA-LU, consisting of a federally required document that allocates transportation funds to a staged, multiyear, statewide, intermodal program of transportation projects; consistent with the statewide transportation plan and planning processes and metropolitan plans, TIPs and processes; the metropolitan TIP must be included in the STIP without change.

Diagonal brace installed to minimize structural movement.

A very hard and strong alloy of iron and carbon.

steering control (SC) zone
Used with interchange/ramp entry traffic models; it is the zone where positioning of the vehicle along a path from the controlling ramp curvature onto the speed-change lane is accomplished.

stopping sight distance (SSD)
The sight distance required to permit drivers to see an obstacle soon enough to stop for it under a defined set of reasonable worst-case conditions, without depending upon speed, gradient, road surface and tire conditions, and assumptions about the perception-reaction time of the driver.

stranded shoe
The device at the end of an eye-bar that holds the wires of each strand for the main bridge suspension cable; the strands loop around the shoes to form a continuous cable from anchorage to anchorage.

A longitudinal beam supporting the bridge deck.

Structure Inventory and Appraisal Rating (SI & A)
A 0-100 rating indicative of a structure’s sufficiency to remain in service (0 worst – 100 best); this is a federal rating measure based on a structure’s structural adequacy, safety, serviceability, functional obsolescence, and essentiality for public use.

A piece or member acting to resist compressive stress.

study area
A geographic area selected and defined at the outset of engineering or environmental evaluations, which is sufficiently adequate in size to address all pertinent project matters occurring within it.

study (or project) limits
The physical end points of a proposed project or study, usually designated at geographic or municipal boundaries, at interchanges, at roadway segments where cross sections change, or at the beginning or end of numbered state traffic routes.

Used to assist in controlling ground water under roadway pavements and various applications.

The parts of a bridge that are below water or land; the piers, or tower foundations and anchorages.

Superpave (Note capital "S" "Superpave" - complete title: SUperior PERforming Asphalt PAVEments)
An asphalt mixture designed to resist the rutting and fatigue cracking caused by heavy loads and extreme temperatures, as experienced with the previous standard.

The parts of a bridge that are above water or land; the towers, main cables, suspender cables and related parts.

supplemental appropriation
An act appropriating funds in addition to those in an annual appropriation act because the need for funds is too urgent to be postponed until enactment of the next regular appropriation act.

suspended span
A simple span supported from the free ends of cantilevers.

suspender cables
The vertical wires are hung at regular intervals connecting the main bridge suspension cables to the deck; the connection is made using a cable band.

suspension bridge
A bridge in which the floor system is supported by tow cables that are supported upon towers and are anchored at their ends.

Movement of freight cars between two nearby locations or trains; switching is a term typically associated with activities that occur in a railcar classification yard or terminal.


The practice of allowing selected employees to work at home or at a remote site rather than the traditional work site to eliminate the commute trip.

temporary pavement marking treatment
This treatment primarily involves the application of paint or tape striping and has been shown to be important for effective vehicle guidance at highway work sites.

A force that pulls or stretches.

through freight train
An express freight train between major terminals.

A member carrying tension, such as a railroad or wire tie.

The authority for the movement of regular trains subject to the rules; it may contain classified schedules and include special instructions.

An intersection that involves three legs, where one leg is perpendicular to the other two legs; there are several types of this intersection, such as plain, with turning lanes and channelized.

A twisting force or action.

The vertical structure in a suspension bridge (or cable-stayed bridge) that holds up the suspension cables.

track car
Equipment, not classified as an engine, which is operated on railroad track for inspection or maintenance; it may not shunt track circuits or operate signals and will be governed by rules and special instructions for trains other than passenger trains.

trackage rights
Rights obtained by one railroad to operate its trains over another railroad's tracks.

The number of motor vehicles in a given location at a given point in time.

traffic calming
A transportation system management technique that aims to prevent inappropriate through-traffic and reduce motor vehicle travel speed on a particular roadway; traditionally, this technique has been applied to local residential streets and collectors, and may include speed bumps, curb extensions, planted median strips or rounded and narrowed travel lanes.

traffic circle
An intersection where traffic moves around a circular center island; some traffic circles have traffic signals, also called a roundabout.

traffic control device
The prime, and often the only, means of communicating with the driving public; these devices (e.g., signs, markings, signals, islands) must be used discriminately, uniformly and effectively to assure correct driver interpretation and response.

traffic count
A tabulation of the number of vehicles passing a certain point over a specified time period; this is often a 12- or 24-hour period.

The number of occupants or the amount of material that a passenger or freight train can hold.

A railroad employee who is in charge of a railway yard.

The movement of a train a distance of one mile; mileage measurement is not increased because of the presence of multiple locomotives in the train.

transit route
A designated, specified path assigned to a transit vehicle.

transit stop
An area where passengers wait, board and transfer between transit vehicles.

A transload facility with full intermodal capabilities is a place where rail or barge freight is combined to take advantage of multiple modes of transportation.

transportation analysis
Corridor analysis is a detailed analysis of a roadway performed for the purpose of obtaining the most accurate projected traffic volumes. The analysis takes into account existing traffic volumes, projected growth, and major traffic generating locations. A corridor analysis will yield projected traffic volumes for every movement allowed on a facility including main lane, ramp, frontage road, and turning volumes.

Design analysis is an analysis is used to determine the number of lanes required to deliver a specific level of service based on a forecast demand volume and given geometric design standards.

Operational analysis is an analytic evaluation of operations on an existing highway segment. The same type of analysis may be applied to evaluate probable operating conditions on a future facility. All traffic and roadway conditions must be specified, as well as traffic volumes. The typical situations which can be resolved through this type of analysis include the comparison of flow conditions for different volume levels and number of lanes. This type of analysis might also be used to establish the impacts of a change in the number of access points along a given section of multilane highway. Another typical application of an operational analysis might be to develop several alternative packages that would be used to improve the level of service or travel speed along a multilane highway.

Planning analysis is similar to design analysis in that the number of lanes needed for a level of service is determined. However, the planning analysis requires much less input of detail, and it uses a very rough estimate for directional design hourly volume and using the design procedures.

transportation management associations (TMA)
This term refers to nonprofit coalitions of local businesses and/or public agencies dedicated to reducing traffic congestion and pollution and improving commuting options for employees. As defined in federal regulations, this term refers to "an urbanized area with population of 200,000 or greater" and "applies to the entire metropolitan planning area." All locations must meet certain standards, and nonattainment. TMAs must meet additional planning requirements.

transportation systems management and operations (TSMO)
The aim of TSMO is to proactively manage and fine-tune the performance of the state's transportation system, particularly by managing or mitigating congestion and incidents. This includes strategies such as monitoring the system through traffic cameras and speed sensors; quickly deploying response resources to incidents; and providing information to travelers through platforms like Iowa 511. TSMO also includes efforts to prepare for and adapt to changing technology, such as connected vehicles and highly autonomous vehicles.

A bridge structure consisting of spans supported upon frame bents.

Enclosed rail freight car for carrying three levels of automobiles.

truck terminal
A facility that serves as a primary gateway for commodities entering or leaving the metropolitan area.

trumpet interchange
A three-legged interchange where a connecting highway terminates and where only a small amount of traffic moves between the terminating highway and one of the two legs of the freeway; the trumpet is laid out so that this minor traffic moves via a 200-degree loop.

A rigid, jointed structure made up of individual straight pieces arranged and connected, usually in a triangular pattern, so as to support longer bridge spans.

truss bridge
A bridge having a pair of trusses for the superstructure.

trust funds
Funds collected and used by the federal government for carrying out specific purposes and programs according to terms of a trust agreement or statute, such as the Social Security and highway trust funds; trust funds are administered by the government in a fiduciary capacity and are not available for the general purposes of the government.

An underground passage open to daylight at both ends.

two-quadrant cloverleaf interchange
A type of partial cloverleaf where most traffic leaving one highway turns to the same leg of the intersecting highway.


Uniform Act
On Jan. 2, 1971, Public Law 91-646, the "Uniform Relocation Assistance and Real Property Acquisition Policies Act of 1970," (Uniform Act) was signed into law. The Uniform Act provides important protections and assistance for people affected by federally funded projects. This law was enacted by Congress to ensure that people whose real property is acquired, or who move as a result of projects receiving federal funds, will be treated fairly and equitably and will receive assistance in moving from the property they occupy.

unit train
A freight train that moves carloads of a single product between two points; by unloading on arrival and returning promptly for another load, such trains can cut costs because they eliminate intermediate stops in yards and reduce cycle times.

upper chord
The top longitudinal member of a bridge truss.

useful field of view (UFOV)
That area surrounding the point of fixation within which one can perform more complex tasks; this might include discriminating among letters or geometric figures, identifying a target against a complicated background display, or combining a secondary task in the periphery with an ongoing task in the forward (central) field of view.


An organized consistent arrangement of five to 15 people traveling together and sharing the expense of the commute van.

vehicle-miles traveled (VMT)
The total distance traveled in miles in a given time period.

vertical curve
The parabolic curve connecting the two approach grades on either side of a hill.

A series of spans carried on piers at short intervals.

visual clear (VC) zone
Used with interchange/ramp entry traffic models, this refers to the zone that provides a buffer between the driver and the end of the acceleration lane, where the driver can either merge onto the freeway in a forced maneuver or abort the merge and begin to decelerate at a reasonable rate.

A rotary, swirling, circular motion of a fluid, like wind or water, the vortex forms a vacuum at its center that draws objects toward it; examples of vortex motion are found in tornadoes and whirlpools, including the small whirlpool formed by water draining from a sink.


A hard-surfaced transportation facility intended and suitable for use by pedestrians, including persons using wheelchairs; walkways include sidewalks, surfaced portions of accessways, paths and paved shoulders.

Warren truss
A triangular truss with sloping members (and no vertical members) between the top and bottom chords, forming the letter "W."

The portion of a bridge beam located between and connected to the flanges.

web members
The intermediate members of a bridge truss, not including the end posts, usually vertically or inclined.

welded joint
A joint in which the assembled elements and members are united through fusion of metal.

welded rail
The standard unit of track structure providing safer, seamless service.

Those areas that are inundated or saturated by surface water or ground water at a frequency or duration sufficient to support, and under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.

wetland and wildlife conservation banks
Large land areas purchased for wetland and wildlife conservation to mitigate transportation impacts on a regional basis.

wide outside lane
A wider than normal curbside travel lane that is provided for ease of bicycle operation where there is insufficient room for a bike lane or shoulder bikeway.

women's business enterprise (WBE)
A business owned and operated by one or more women.



The railway employee designated as being in charge of all operations in a yard.