I-70 VSL Sign Project FAQs

Frequently Asked Questions

  1. What is a variable speed limit (VSL) sign?

A variable speed limit sign is an electronic version of a regular speed limit sign with an LED display of the regulatory speed limit number (i.e. the enforceable speed limit) which can be changed to best suit conditions on the highway. The VSL signs will change the speed along this stretch of eastbound I-70 as needed based on traffic speed and volume, weather conditions, road conditions, and traffic incidents.

VSL Sign

  1. What is the benefit of VSL signs?

VSLs react to real-time congestion and incidents on the corridor, reducing speeds to a speed limit reasonable to the situation to prevent crashes and “stop and go” traffic. VSLs have been shown to improve safety and operations on highways nationwide.

  1. When will the speed limit change?

It’s important to note the speed limit will not change all the time, ONLY when there are bad weather conditions or congestion that warrant a change. One example is if there is a crash ahead on the highway, the variable speed limit signs can be changed to slow traffic down before reaching the back of the traffic queue to reduce the chances of a secondary crash. Similarly, if there is a snow storm on the corridor that may cause slick conditions, the speed limit will be lowered to slow drivers down.

  1. What is the minimum speed limit that might be displayed on the VSL signs?

In the case of an incident, inclement weather, or heavy congestion, the minimum speed limit that will be utilized on these VSLs is 40 MPH in dry conditions and 30 MPH in icy or wet conditions. By setting speed limits that are reasonable considering the traffic and weather, the traveling public will come to expect that a lowered speed limit indicates a true need for slowing conditions ahead and will lead to better trust in the posted speed limits. 

  1. Where are the VSLs installed?

The VSL signs for this project are along eastbound Interstate 70 from Empire Junction to just east of Idaho Springs. There are a total of 26 VSL signs in this project. This included replacing 13 aging VSL signs, and installing 13 new VSL signs. This creates 13 locations along eastbound I-70 between Empire and Idaho Springs where there is a VSL sign on both the left and right shoulders so drivers in any lane can see the speed limit. The signs are spaced about a mile to half mile apart and are placed near interchanges for all drivers to best see the signs.

The I-70 mountain corridor is a beautiful route and special care was taken in determining how many VSLs are needed for full operation of variable speed limits while keeping sign clutter at a minimum. CDOT mounted VSLs and monitoring devices on existing infrastructure as much as possible.

  1. Is the speed limit posted on a VSL the recommended speed limit or enforceable speed limit?

The speed limit posted on VSLs is the enforceable speed limit, it is not a recommended or suggested speed limit. This means that a driver travelling at speeds greater than what is posted can be be ticketed for speeding.

  1. Does the speed limit on a VSL apply to all lanes of traffic?

Yes, the speed limit posted on a these VSL signs applies to all eastbound lanes between Empire and Idaho Springs, including the Eastbound I-70 Mountain Express Lane (also known as the Peak Period Shoulder Lane).

  1. Will the speed data be available on cotrip.org?

Yes, the posted speed limit will be available on cotrip.org following the testing period. 

  1. How will the VSL signs be tested?

The VSL signs were tested once they were built to make sure they can be controlled by CDOT traffic operators in the Eisenhower Johnson Memorial Tunnels. CDOT will continue to monitor the posted speed limits to make sure the software is correctly evaluating the traffic and weather conditions, and recommending appropriate limits.

If there are any data or equipment malfunctions, the VSLs will default to the maximum allowed speed limit for that section of I-70, such as 65 MPH. A CDOT traffic operator will be notified of the issue and will quickly resolve it.

In the long term, CDOT will evaluate the improvements in safety and operations from implementing these VSL signs on the eastbound I-70 corridor

  1. Are VSL signs being used anywhere else in Colorado?

Yes! There are VSLs being used in Glenwood Canyon; there are also upcoming efforts to use variable speed limits on other areas in the state.

However, this project is the first to operate VSLs with the use of a bespoke software. This software was developed with a team of national highway safety experts; it will draw upon a relationship between increasing traffic volumes and crash rates, as well as how inclement weather affects the roadway, to recommend speed limits.