Watch Part 3 of our school zone safety series

According to the American Automobile Association, driving at inappropriate speeds—either faster or slower than posted limits—nearly triples the odds of being involved in a crash or near-crash.

Slowing down traffic saves lives: according to the Texas Transportation Institute, in incidents with a vehicle traveling at 40 mph, 1 in 10 pedestrians struck will survive, but if the vehicle is traveling 20 mph, 9 in 10 pedestrians struck will survive.

In the wake of increasing pedestrian fatalities in the US and Canada, many cities have begun adopting traffic calming programs to help slow traffic and save lives. Traffic calming refers to the use of physical road design or other measures to slow vehicles as they move through commercial and residential neighborhoods. Treatments like sidewalk extensions, speed humps, street narrowing, and more can calm traffic and improve safety for all road users.

Another effective traffic calming measure is to use radar speed signs that show drivers how fast they’re traveling, allowing them to self-correct their speeds and slow down.

Part 3 of our school zone safety series will look at radar speed signs as a proven traffic calming treatment for slowing down vehicles in school zones and beyond.

We will focus on radar speed sign effectiveness, how the technology works to improve driver awareness, and how it can fit into a school zone safety plan.

Keep in mind this is a general guideline only: your state and/or local jurisdiction may have different requirements for radar speed sign placement standards to meet their unique safety concerns.

Radar speed signs—also known as driver feedback signs, speed monitoring displays, and a variety of other names—help drivers refocus their attention on their current speed and self-correct to the posted speed limit. They can be placed in locations where drivers regularly exceed the posted speed limits. One common location is upstream of school zones, in preparation for the change in speed.


Where and How to Install Radar Speed Signs

According to the 2009 MUTCD, the Speed Limit R2-1 sign shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency based on an engineering study. The similar S5-1 School Speed Limit assembly shall be used to indicate a reduced school speed limit zone that has been established based upon an engineering study or where specified by a statute. As we covered in our video on school zone beacons, School Speed Limit signs should be installed at a minimum of 200 feet from the school grounds or as close to the point the reduced speed limit begins. Check Chapters 2B and 7B of the MUTCD for more information on these speed limit signs.

Like most signs, these sign types should be installed a minimum of 7 feet from the bottom of the sign to the top of the curb or traveled elevation. In rural areas, this shall be 5 feet from the bottom of the sign to the elevation of the near edge of the pavement. If installed above a sidewalk, a minimum of 7 feet is always required.

In order to reinforce the speed limit message stated by the R2-1 and S5-1 signs, a changeable message sign may be used to display to approaching drivers the speed at which they are traveling. The category of “changeable message signs” includes radar speed signs. These signs should almost always supplement conventional signs, rather than substitute them.

The MUTCD allows changeable message signs to be on the same sign post or on a separate sign post adjacent. If on the same sign post, the sign may be mounted 1 foot lower than the heights previously mentioned.

According to MUTCD guidelines, changeable message signs, including radar speed signs, should use uppercase letters on the digital display. For roadways with speed limits less than 45 mph, typical for most school zones, the minimum letter height should be 12 inches. However, the legibility of the sign at a distance can improve with larger digit signs—and because of this, many cities have opted for 15-inch digit size signs.

When changeable message signs are installed, the legend, “YOUR SPEED XX MPH” or a similar variation should be displayed on the sign. The color of the changeable message legend should be yellow on a black background.

Messaging with characters or symbols other than letters and numerals is not recommended by the MUTCD, and strobe light technology is strictly prohibited (as stated by the FHWA). However, certain states and jurisdictions may include some of these optional message types.

You can download our condensed MUTCD Guidelines for Radar Speed Signs to learn more.

Radar speed signs provide immediate feedback on driver speed, helping drivers self-correct. The digits flash when drivers are exceeding the posted speed limit and may also include an optional “SLOW DOWN” message programmed to flash at pre-defined speeds. The higher the speed, the faster the flash. A high-speed cutoff threshold option can be set to prevent drivers from racing the sign.

A common safety treatment, there are many varieties of radar speed signs on the market. City and county engineers in California indicated in a survey that they value a high-quality radar speed sign with good visibility in all lighting conditions, so drivers have no issues reading their speed on the display. This means the sign needs a high contrast between the black background and the LEDs, without a ghosted “88” showing up behind the lit numbers. They also prefer an easy-to-read font with smooth, recognizable digits and letters.


Radar Speed Sign Effectiveness

So, are radar speed signs effective at slowing down vehicles? In a study in Utah, 68.2% of drivers self-reported that radar speed signs are helpful or very helpful at informing them of their speed while driving, and 66.1% agreed or strongly agreed they are effective at causing them to slow down.

The statistics show these driver perceptions to be accurate. In a study comparing speeds before and after radar speed signs were installed at a school zone speed limit sign, the percentage of vehicles exceeding the school zone speed limit of 35 mph was reduced from 95.3% to 34.1%, while the 85th percentile speed dropped from 50 to 40 mph. Even after 4 months, the percentage of vehicles exceeding the speed limit was 43.9%, while the 85th percentile held at 42 mph.

Why do these signs work? Research shows that brain waves during a habitual task—like driving to work—are in theta state, and they must be shifted to beta waves in order to react quickly. In simple terms, the unfamiliar warning sign can help the brain shift out of autopilot to an engaged state, helping drivers recognize their own behavior and self-correct.

For law enforcement, this means a gentler approach to traffic control that also helps with budget and staffing issues for the force.


Scheduling and Data Collection

In school zones, radar speed signs can include a calendar function to help enforce the lower speeds in the designated time period when these speeds are in effect, usually within a window of about an hour when school begins and an hour around the time school ends. The rest of the time, these signs can remain black to help drivers recognize the lower speed limit is not required.

Even if radar speed signs are not a permanent solution in a given location, they can still be used to measure data.

The technology can track traffic speeds, traffic density, and similar data, and the signs can even do so in a “stealth mode,” allowing them collect data while the digital display is off. If and when the display is turned on at a later date, the data collected with the sign in stealth mode will show how activating the sign affected local traffic speeds.

Local policymakers, school administrators, and community groups can use this data to assess the current safety measures in place and determine if an activated radar speed sign is necessary or if other resources are required to keep both pedestrians and vehicle occupants safe.

These signs can fit into a school zone safety plan, and funding is often available for such devices through a Safe Routes to School program or similar initiative.

Radar speed signs are invaluable for helping drivers quickly take notice of their speed, understand the message, and self-correct to the appropriate speed as they approach school zones—keeping children and other pedestrians safe.


Learn more

Check out the rest of this video series to learn about other possible school zone treatments.