Pavement Marking Changes

The Iowa DOT is adopting 6-inch wide lines as the standard for interstates and primary highways, aligning with the national movement. This wider marking enhances safety, improving visibility and reducing run-off-the-road crashes. It also facilitates detection by vehicle automation and lane-assist systems, preparing for future technology.

Next Steps

We have been testing 6-inch wide lines on various projects and have received positive feedback. Within the next few years, we will begin installing 6-inch lines on all construction projects and existing lines will be repainted at 6 inches. To prepare for this change, specifications, standards, tabulations, and software packages are being updated to make 6-inch lines the default.

The 4-inch wide line styles will not be removed. We recognize that the 4-inch wide lines still have a use and we will continue to install and refresh pavement markings at 4 inches until funding is established for the transition. These changes do not alter design or construction workflows; they establish the groundwork to ensure our documentation is ready for a future switch to 6-inch lines.

When Changes Go Into Effect

Please see the information and links below for changes that will go into effect with projects let in April 2024 and after.

Specification Changes

The specification changes have been approved so that 6-inch width is the method of measurement (2527.04 B). This change will be posted online before April 2024.

Standards

• PM-110 - Pavement Marking Line Types
• PM-115 - Grooving For Pavement Markings

Tabulations

The Tab program has been updated to include these changes. Login to the Project Design Tabulations Application
 

Pavement Marking Changes 

4" Paint; 4" Factors

\(\frac{\text{4" Paint, 4" Factors}}{\text{4" Paint, 6" Factors}} \approx 1.5\)

\(\text{4" Paint, 6" Factors} \times 1.5 \approx \text{4" Paint, 4" Factors}\)

4" Paint; 6" Factors
 

\(\frac{\text{4" Paint, 4" Factors}}{\text{4" Paint, 6" Factors}} \approx 1.5\)

\(\text{4" Paint, 6" Factors} \times 1.5 \approx \text{4" Paint, 4" Factors}\)

• Multiplying totals of 6-inch line factors by 1.5 will give approximate totals of 4-inch line factors
• The difference between calculated 4-inch line factor totals and previous 4-inch line factor totals is approximately 0.6% high.
• This difference is caused by rounding of the 6-inch line factors (0.66666666 rounded to 0.67).

It is recommended that agencies to list the unfactored line lengths and/or the centerline miles to be painted in the bid request for information only.  This may help contractors better understand the change in measurement factors and reduce the potential for confusion.

New Bid Item Code

New Paint Factors

Factors can be calculated by:

• Factor = (PL/RL)X(LW/6)
• PL = Painted Length
• RL = Repeat Length
• LW = Line Width