UDOT signs may soon be more retroreflective.

Many freeway signs don’t need active lighting due to the high level of retroreflectivity of sign materials.

Gone are the days when all freeway signs require active lighting to be seen at night. The sheeting material used to face modern signs is highly retroreflective — meaning the light bounces off of the sign right back to the light source. Many freeway signs don’t need active lighting due to the high level of retroreflectivity of sign materials.

UDOT requires that signs be faced with retroreflective Type 9 sheeting. New Type 11 sheeting, which has a higher level of retroreflectivity, can be used. Contractors who bid for UDOT projects can select the most appropriate sheeting for the job.

UDOT uses active lighting on all system to system interchanges and other places where the roadway is complicated or the signs use a lot of text. For example, the I-15 to I-80 interchange in Salt Lake County has active lighting to assist state-to-state motorists. For other locations, UDOT uses active lighting on a case-by-case basis. Motorists who observe lighting fixtures that may not be working as intended should call 801-975-4000 to report the location.


Retroreflectivity on signs can be diminished over time due to weather, vandalism or other damage. Ongoing evaluation of signs, especially those that have been in place for several years, is important to maintaining safety on UDOT facilities.  At UDOT, maintenance workers conduct inspections as part of an overall plan to make sure signs meet new federal standards.

Visual inspection at night is critical when evaluating how effectively retroreflective signs are doing their job. Signs with small areas of damage may be readable during the day, but “the effect of that damage at night could be huge” says UDOT Operations Design Engineer Wes Starkenburg. For example, a paint ball hit can prevent the reflective material from shining in headlights.

A retroreflectometer can be used to take objective measurements. Several measuring devices are available – some require actual contact with the material being measured.

When signs get too old, worn or damaged, single signs are replaced, but typically UDOT identifies interstate segments where a series of signs could be improved. Replacing signs in a segment gives UDOT the chance to update signs that work together to provide clarity and consistency for road users.


UDOT uses materials that have been tested by ASTM International, an organization that tests products to set standards for many industries. Sheeting materials are tested in a lab that’s set up to approximate how road users will see signs at night with headlights. Testers evaluate sheeting attributes including color, gloss, opacity, and texture, and take objective measurements.

5 thoughts on “THESE GO TO 11”

  1. Garrett

    Thanks for the informative blog post. I’ve been looking out for places that I think can use working street lights for the purposes of safety; one such location is the loop ramp from northbound 1300 East to westbound I-80 in Sugar House. Last time I passed through there at night, not one light fixture was operational. Perhaps a loop ramp would be a good place for working street lights? Just a suggestion.

  2. Catherine Higgins

    I have forwarded your question to UDOT Traffic and Safety and will provide an answer as soon as possible.

  3. Gayle

    Why don’t u start by changing the paint on our roads instead of white u can’t even see with rain or snow use the Florence green color that u can see so much better at night and in weather.

  4. Catherine Higgins

    Paint colors are designated by the Manual for Uniform Traffic Control Devices. Departments of Transportation and other agencies that maintain publicly accessible roads are required by law to follow the MUTCD. Keeping a uniform look from road to road and state to state helps motorists recognize lane markings without having to become familiar with new rules. For example, yellow is used universally to separate opposing traffic. Florescent green is used on some signs and on pavement markings near schools. You may be interested in this blog post about reflective paint.

  5. Catherine Higgins

    The UDOT lighting crew has been working to repair vandalized lighting circuits along I-15, I-80, SR-201, and I-215. Thieves have stolen thousands of feet of copper wire from interstate lighting circuits. Our goal during the past year and a half has been to repair and secure the lighting circuits. The next phase is to begin a systematic relamping of the I-15 corridor working northward from 10600 South. You will likely see crews working on Sundays performing this work. First they will re-lamp the high mast lighting, then the off ramp lighting and finally the underpass lighting. Overhead sign lighting that is located within areas of continuously lit interstate will not be relamped. A project is proposed to replace the sign sheeting on these signs with an improved reflective sheeting. Lighting overhead signs will no longer be necessary. Elimination of sign lighting will reduce energy demand and cost.

Leave a Comment

Your email address will not be published. Required fields are marked *