By Bryant Ficek, PE, PTOE
The best place to start when talking about traffic signal warrants is to understand the definition of a warrant itself. According to the Manual on Uniform Traffic Control Devices (MUTCD), a warrant is a threshold condition based upon average or normal conditions that, if found to be satisfied as part of an engineering study, shall result in analysis of other traffic conditions or factors to determine whether a traffic control device or other improvement is justified.
With that being said, warrants are not a substitute for your judgement as an engineer. Warrants are simply guidelines that we use as part of traffic studied to help determine the best course of action in a particular scenario.
There are different types of warrants, all dealing with traffic control, which include:
- Side-Street (Two Way) Stop Control
- All Way Stop Control
- Traffic Signal Control
- Roundabout Control
For this piece, the focus is specifically on traffic signal warrants and the guidelines that are in place to help determine when installing or improving upon a traffic signal is justified.
The Manual on Uniform Traffic Control Devices (MUTCD) lists 9 warrants for evaluating traffic signals:
- Warrant 1, Eight-hour vehicular volume
- Warrant 2, Four-hour vehicular volume
- Warrant 3, Peak hour vehicular volume
- Warrant 4, Pedestrian volume
- Warrant 5, School crossing
- Warrant 6, Coordinated signal system
- Warrant 7, Crash experience
- Warrant 8, Roadway network
- Warrant 9, Intersection near a grade crossing
The first three warrants are generally the most used and easiest to collect the necessary data (traffic counts). Other warrants can usually be ruled out if not applicable to the specific intersection you are reviewing. For example, you won’t be using Warrant 5, School Crossing, if there’s not a school in the immediate area. It’s also a good idea to check with the governing agency to see if all warrants are equal in their eyes. For instance, the Minnesota Department of Transportation looks to Warrant 1 to be met before a traffic signal is installed.
The three primary pieces of data to collect when evaluating traffic signal warrants are: layout of intersection (existing or future), speed limits, and volumes (we like to include turning movements, pedestrians, cyclists, etc.). Other relevant data to collect includes crash data, progression of other signals in corridor and proximity to schools, parks or other high-pedestrian areas. With this information, the warrants are fairly straight forward. Examine the thresholds, compare against the information and data you’ve gathered, determine if the threshold is met and the warrant is satisfied.
With practicality and efficiency in mind, we’ve put together some tips and tricks to consider when evaluating the traffic signal warrants:
- Use the 85th percentile speed instead of the posted speed limit (check out our article 85th Percentile Speed Explained)
- Bicyclists can be counted as either pedestrians or vehicles in your analysis
- Where there is no indication as to which is the major or minor road at an intersection, run your analysis both ways to get a clearer picture
- In many states, if you have right turn lanes at an intersection, you can remove the right turning lane volume and discount the right turn lane from the total number of approach lanes
- In a situation where you have a significant number of left turn movements from an approach, you could look at those left turns as your minor leg and the conflicting thru volume as the major leg
- Last, but not least, use our Traffic Signal Warrant Analysis tool to assist you with accurately analyzing your data and warrants
Warrants are great guidelines for determining whether an intersection justifies the installation or improvement of a traffic signal. While they are no substitute for your expertise and judgement as a traffic engineer, they are an extremely useful way to help you determine the next course of action based on the data you’ve collected.
Want more information on traffic signal warrants? Check out these tools:
- Traffic Signal Warrants webinar recording. This webinar reviews the MUTCD’s language on traffic signals, and presents simple tools to evaluate traffic signal warrants.
- Essential Warrant Analysis Spreadsheet (Warrants 1 – 3). This easy-to-use spreadsheet does all-way stop sign warrants and signal warrants 1 -3. Check out our short video on how to use the spreadsheet.
- Complete Warrant Analysis Spreadsheet (Warrants 1 – 9). A low-cost solution for analyzing traffic signal warrants and multi-way stop sign warrants. Includes warrants 1 – 9. Watch our short video on how to use the spreadsheet.
- Traffic Corner Tuesday Webinar Series. 30-minutes of free traffic engineering best practices.