by Leigh Ratcliffe
One way to make streets safer for all is to lower the speed limit. In Encinitas, speed limits have been lowered around the city in the last few years. However, many travelers still drive fast!
Adding more police officers is a costly way to enforce speed limits. Are there other ways beyond writing tickets that can reduce driving speeds? Are there other, more affordable ways to change driver behavior?
Yes there are! At least on a temporary basis. Read on to learn about
- VMS
- Speed Signs
- Red Light Cameras
Variable Message Sign
A Variable Message Sign (VMS) is an electronic road sign that displays real-time, programmable information to drivers, providing updates on traffic conditions, accidents, road closures, travel times, and other safety alerts to help manage traffic flow and improve safety.
The main purpose of VMS is to provide drivers with real-time information about traffic congestion, accidents, roadwork, weather conditions, and other critical travel advisories. For example, the signs on the freeway that tell you how long it will take to get to various places, or the portable signs that alert you to construction ahead.
VMS signs are also used for public service announcements, like “Don’t Drink and Drive.”
Signs alerting to road conditions are either temporary or change depending on the conditions (1 hour vs 30 minutes to get to the 710 freeway). Public service announcements however, are static messages, and drivers can become habituated to their messaging. There is also a lot of regulation around how to write a VMS message (a whole manual, in fact. Check out the Manual on Traffic Control Devices if you want a deep, deep dive).
Do VMS signs work? Generally, the answer is yes.
Many studies, like this one from the Federal Highway Administration, conclude that messaging changes driver behavior. These studies get their data from driver questionnaires and ask questions like did the driver understand the message and did it change their driving behavior. I did find one interesting study that added traffic data obtained from the VMS signs and from toll road gates (full disclosure – I was only able to read the abstract and introduction). Basically they could ask drivers about the messaging but also look at how many vehicles went by the sign, what kind they were, and what speed they were going. The conclusion? “For the speed reduction behavior, in 87.50% of the studied messages, the results indicate that the messages failed to induce the desired change in behavior.”
So maybe the answer is no, they don’t work? Clearly more studies are needed.
Speed Signs
Vehicle speed feedback signs or driver feedback signs use radar to detect the speed of passing vehicles and display this speed on a digital screen to alert drivers.
These signs are most commonly used around places that have reduced speeds, like schools. They are also used when speed limits transition from a higher speed to a lower speed, most often when approaching a town or populated area. These signs also have a lot of rules in the Manual on Traffic Control Devices, but because they only show speeds and not phrases they don’t need any rules for what they display. They are also not as prone to habituation because the “message” on the sign is always changing.
Interestingly, these signs can also track data about vehicles such as how many pass the sign and how fast they are going.
Do speed signs work?
Again, the answer is yes … generally.
One study by the Federal Highway Administration looked at the long-term effect of speed signs on “speed reduction transition zones” and found there was a significant decrease in vehicle speeds. The National Highway Traffic Safety Administration summarizes quite a few studies generally showing beneficial effects of speed signs.
One key finding from most of these studies is that the speed cameras only work where they are installed (drivers speed up once past the sign) and only when the sign is there.
So again, maybe the answer is no, they don’t work that well?
Red Light Cameras
Red light cameras are mainly used to capture images of drivers committing traffic violations – most commonly, speeding and red light running.
Red light cameras are installed at intersections known for a high number of crashes or red-light-running violations to improve safety. There is lots of guidance around how to utilize this tool, one example is the report Automated Enforcement in a New Era by the Governors Highway Safety Association.
Studies on the effectiveness of red light cameras are mixed. They reduce some types of crashes but have been shown to increase rear-end crashes. This quote from the report on Safety Impact of Speed and Red Light Cameras report, created by Congress.gov, sums it up pretty well:
In numerous studies, red light cameras have been shown to decrease the number of both red light violations and crashes involving injuries and fatalities at signalized intersections. There is some evidence that red light cameras, while reducing right-angle crashes at intersections, can lead to an increase in rear-end collisions as drivers change their behavior to avoid entering
intersections when the traffic signal is yellow and are run into from behind by more aggressive drivers. Such collisions are typically less destructive than the right-angle collisions resulting from red light running, thus red light cameras reduce overall crash severity. Not all studies have found increases in rear-end collisions; nor have all studies found statistically significant reductions in overall crash severity.
Do red light cameras work? Once again, the answer is … maybe?
Conclusions
VMS signs, speed signs, and red light cameras are all good tools to change driver behavior, but they are not going to solve the problem of unsafe driving on their own.
VMS signs should be used on a temporary basis and should be connected with a public safety announcement that is being broadcast on multiple platforms. Speed signs can be great for slowing down drivers but drivers quickly speed up after the sign or if the sign is removed. Red light cameras are not well-liked by the public and could increase rear-end crashes.
We need to be using these tools on a temporary or even an emergency basis. Long term, infrastructure changes are what will change the behavior of drivers and make our streets safer for all.
