6A-11: Stop Sign Islands

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General

Intersections designed for large vehicles (e.g., semi-trucks) need a large area of pavement to accommodate the vehicle’s swept path.  The resulting large intersection can make it difficult to properly place a stop sign outside of the paved area where it is visible to drivers (refer to Section 2A-8 within the Traffic and Safety Manual for guidance on the proper placement of a stop sign).  A stop sign island provides an area to place a stop sign where it is visible to a driver.  Stop sign islands should only be used if the intersection geometry does not allow for proper placement of a stop sign outside of the paved area.

The primary function of a stop sign island is to place a stop sign near the stop bar.  Secondary functions are: defining vehicle paths, delineating unused pavement areas, and reducing conflict severity by providing safer merging angles.

\({\Large Quick\ Tips:}\)

  • In general, the use of raised stop sign islands is discouraged.
  • Include painted islands at intersections, unless the District Office requests raised islands.
  • Refer to Section 6A-2 for guidance on selecting a design vehicle.
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Island Type

Stop sign islands can either be raised (curbed) or painted (flush).  Painted islands have fewer impacts to snow removal operations and have less maintenance costs.

\({\Large Attention:}\)

Include painted islands at intersections unless the District Office requests raised islands.

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Design

Stop sign islands should direct stopped drivers to a place where they can comfortably see other vehicles approaching from their left side.  The island should also be large enough to command attention and give lateral clearance to the sign.

Driver’s Viewing Angle

Intersecting roadways are usually designed to meet at or near 90 degrees.  This maximizes visibility for a stopped driver to view approaching vehicles.  A stop sign island added to the intersection will affect the driver’s position at the intersection and visibility to approaching vehicles.

A stop sign island has a triangular shape (see Figure 1).  The corner of the island pointed down the primary road should have an interior angle greater than 60 degrees.  Drivers have to rotate their head and look back over their shoulder to view approaching traffic when the interior angle is less than 60 degrees.  This is uncomfortable for drivers, especially older drivers.  The degree of head rotation typically decreases with age.  Figure 1 illustrates a driver’s viewing angle.

\({\Large Note:}\)

Intersections designed for a semi-truck and with an interior angle of 60 degrees provide enough space such that drivers in passenger cars can orient themselves at the intersection close to perpendicular with the cross street.

Two intersection‑viewing diagrams comparing a shallow approach angle that restricts a driver’s sight line with a wider approach angle that improves visibility.

Figure 1: Illustration of a driver’s viewing angle.

Skewed Intersections

Intersections that do not meet at near 90 degrees, and cannot be aligned to do so, will need to have the island designed for a comfortable viewing angle.  Account for the intersection angle when calculating the viewing angle.  Refer to the Design Examples section below for guidance on how to account for the intersection angle.

Island Dimensions

Guidance within the AASHTO Greenbook suggests corner islands (stop sign islands) should have an area of at least 100 ft2 for both urban and rural intersections.  The minimum areas listed within the Greenbook are 50 ft2 for urban intersections and 75 ft2 for rural intersections.  This guidance provides an island large enough to command attention and place the sign(s).

AASHTO guidance also suggests islands should not have a length of less than 12 feet on a side after rounding the corners of a raised island (round corners with a radius of 1 to 2 feet).  15 feet is sufficient length between the points for painted islands.  The dimensions allow space for the sign and lateral offsets to the sign from the adjacent lanes.  See Figure 2 for details of stop sign island dimensions.

\({\Large Note:}\)

Painted islands can have smaller dimensions, but the dimensions should accommodate a lateral offset to the sign(s) within the island.  MUTCD criteria states to provide an offset of at least 2 feet from an adjacent lane to a sign.  Refer to the Traffic and Safety Manual for intersection signing typicals and figures.

 

Side‑by‑side geometric comparison showing a 15‑ft‑wide triangular island and a modified 12‑ft‑wide version with rounded 1‑ft‑radius corners.

Figure 2: Dimensions of painted and raised stop sign islands.

Stop Sign Islands within a Median Opening

Stop sign islands are sometimes added to a median opening to place the stop sign (or yield sign) closer to the stop bar (or yield bar).  These islands (see Figure 3) are smaller than standard islands and are usually added to intersections with a far side crash pattern.

Rounded triangular loop with a 5‑ft width, 3‑ft height, and 2‑ft corner radius.

Figure 3: Dimensions for small stop island in median opening.

Offset

The minimum offset from an edge of traveled way to the island is 2 feet.  For rural intersections, the face of island near the through roadway should have an offset equal to the shoulder width (projected through the intersection) plus an extra 2 feet.  The offsets to face of a curb for raised islands also apply to painted islands.  Refer to Figure 4 for details of offsets to an island.

Intersection‑corner layout showing a vehicle’s turning‑tire path with 2‑ft clearance offsets from the mainline shoulder and the approach‑lane edge.

Figure 4: Dimensions small stop island in median opening.

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Curb Type

Raised islands in a rural high-speed environment should use a 4 inch sloped curb (see PV-102).  

Refer to Section 3C-2 for guidance about selecting a curb type and size.

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Example Problem 6A-10_1: Designing an Intersection with a Painted Stop Sign Island

Design an intersection to accommodate the turning path of a semi-truck with a stop sign island.

Given:

Perpendicular intersection between two-lane roadways.

Two-way stop controlled intersection.

Intersection design vehicle – WB-67.

Diagram of a T‑intersection with dashed centerlines and two stop signs on side roads controlling entry to the main road.

Figure 1: Intersection with two-way stop control.

Solution:

  1. Design the island
    1. Locate the face of the island near the mainline and approach lane.
Intersection‑island offset diagram showing shoulder and approach‑lane references with island‑face lines placed 2 ft from each.

Figure 2: Offsets to island.

  1. Design the edge of the island near the mainline

 

Intersection layout showing road edges, dashed centerline, 15‑ft spacing between reference lines, and a red L‑shape marking a corner.

Figure 3: Side of an island with a desirable dimension.

  1. Determine the angle of the island pointed down the mainline.
Intersection diagram with perpendicular roads, dashed centerline, and a red 60‑degree triangular marker beside vertical reference lines.

Figure 4: Interior angle pointed down the cross street.

  1. Intersect lines to design the island.  Check the area and clearance to the sign(s) within the island. 

 

Intersection clearance diagram with perpendicular roads, two 2‑ft minimum offsets, and a red right‑triangle showing required spacing.

Figure 5: Offsets from the island to the sign.

  1. Design the edge return
    1. Create the vehicle path
Corner‑design diagram with perpendicular roads, a blue arc tangent to 6‑ft offsets, and a red triangular clearance area at the corner.

Figure 6: Turning path offsets and arc tangent to the offsets.

Discussion: When determining the offset from the island, the designer should use a distance equal to ½ the design vehicle width plus an additional 2 feet, as the minimum distance.

To develop the turning path, the designer can place tangent to each offset.

  1. Simulate the selected path and check offset to the island.
Intersection turning diagram with green front‑tire, red rear‑tire, and blue vehicle‑path curves showing a 2‑ft curb clearance.

Figure 7: Design vehicle path with offset to the island.

  1. Design the edge return.
Corner‑design diagram with main and side road edges, a red dashed curb‑return curve, a green clearance curve, and a labeled edge‑return.

Figure 8: Edge return for the intersection.

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Example Problem 6A-10_2: Design a Stop Sign Island for a Skewed Intersection

\({\Large Quick\ Tips:}\)

Intersections with acute angles less than 75 degrees are usually realigned to be perpendicular.  Refer to Section 6A-08 for guidance.

Case 1: Right-skewed Intersection

Given:

Right-skewed intersection between two-lane roadways.

Two-way stop controlled intersection.

Intersection design vehicle – WB-67.

Intersection diagram with a horizontal road and a diagonal road meeting at an 85° angle, shown with two stop signs on the diagonal approaches.

Figure 1: Intersection with two-way stop control.

Solution:

Design the island

  1. Locate the face of the island near the mainline and approach lane.

 

Intersection‑angle diagram with horizontal and diagonal roads meeting at 85°, 60°, and –60°, plus a red triangular construction.

Figure 2: Intersection with two-way stop control.

  1. Check the area and clearance to the sign(s) within the island.

Case 2: Left-skewed Intersection

Given:

Left-skewed intersection between two-lane roadways.

Two-way stop controlled intersection.

Intersection design vehicle – WB-67.

Intersection diagram with a horizontal and diagonal road meeting at an 85° angle, shown with a curved angle label and two stop signs.

Figure 3: Left-skewed intersection with two-way stop control.

Design the interior angle of the island

  1. Locate the face of the island near the mainline and approach lane.
Intersection‑angle diagram with parallel horizontal lines, a diagonal road edge, and a red triangle marking 60° and 85° angles.

Figure 4: Intersection with two-way stop control.

  1. Check the area and clearance to the sign(s) within the island.
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Chronology of Changes

Chronology of Changes
DateRevision Description
  
  
7/28/2026New 2026 Update
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