I mentioned yesterday that Traffic Engineering is as much a behaviorial science (the psychology of drivers) as it is a hard science of numbers and because of that I think its one of the hardest engineering disciplines going. Hydraulic engineers can predict with a high level of accuracy what water will do under various hydraulic conditions and Civil Engineers that specialize in wastewater have predictable formulas for what happens in sewer pipes for all that stuff that flows downhill to get to the wastewater plant. The Traffic Engineers have some terrific, well researched, and statistically valid models too but much to their dismay people aren’t nearly as predictable as water. Water does what it’s told, people not so much. I’m not saying Traffic Engineers are perfect but I honestly believe that their success rate would be higher if us drivers actually did what we were supposed to do behind the wheel.
I wasn’t planning a civics lesson in good driver behavior but in the interest of safety I’m willing to play the role of Jiminy Cricket and be your conscience. But even old Mr. Cricket had trouble explaining right and wrong Click Here when it came to traffic temptations.
The axiom that I find most appropriate to the Traffic Engineering world is the law of unintended consequences. Many times what appears to be a logical traffic solution to the general driving public, e.g., throw in a stop sign, drop in a new traffic signal, add speed bumps, etc. can be a bad idea and bad ideas in the traffic world means someone gets hurt. It’s usually not that the idea is bad, it’s the specific application of it. I know it seems counter-intuitive but just because traffic signals work really well at a lot of intersections doesn’t actually mean they’ll work well everywhere. Too much of a good thing isn’t always so good in traffic circles.
Here’s a couple of good answers and explanations from the Institute of Traffic Engineers that relate to one of the most common questions we get asked:
WON’T A ‘TRAFFIC SIGNAL’ REDUCE CRASHES AT OUR INTERSECTION?
Traffic signals don’t always prevent crashes, In many instances, the total number of crashes and injuries increase after they’re installed.
Where signals are used unnecessarily, the most common results are a reduction in right-angle collisions but an increase in total crashes, especially the rear-end type collision. In addition, pedestrians are often lulled into a false sense of security.
In deciding whether a traffic signal will be an asset and not a liability, traffic engineers evaluate the following criteria:
*Does the number of vehicles on intersecting streets create confusion or congestion?
*Is traffic on the main street so heavy that drivers on the side street will try to cross when it is unsafe?
*Does the number of pedestrians trying to cross a busy main street create confusion, congestion or hazardous conditions?
*Does the number of school children crossing a street require special controls for their protection? If so, is a traffic signal the best solution?
*Will the installation of a signal allow for continuous, uniform traffic flow with a minimum number of vehicle stops?
*Does an intersection’s crash history indicate that a signal will reduce the possibility of a collision?
Traffic engineers compare the existing conditions against nationally accepted minimum standards established after many years of studies throughout the country. At intersections where standards have been met, the signals generally operate effectively with good public compliance. Where not met, compliance is generally reduced resulting in more hazards.
While a properly placed traffic signal improves the flow and decreases crashes, an unnecessary one can be a source of danger and annoyance to all who use an intersection: pedestrians, cyclists and drivers.
WHAT IS THE HARM OF INSTALLING AN UNWARRANTED TRAFFIC CONTROL DEVICE?
Traffic Control Devices (TCD’s) such as Traffic Signals, Stop Signs and Speed Limit Signs are installed to regulate traffic flow and improve safety. The installation of these TCD’s should be based on the professional judgement of Traffic Engineers after careful study of the location to be controlled. The study should consider such factors as crash frequency and type, vehicle speeds and traffic volumes.
On occasion, an elected official, with a true “politician’s” zeal to please everyone, influences the installation of a traffic control device against the advice of the Traffic Engineer, The elected official’s motivation is often an angry or persistent citizen rather than the objective professional judgement of the Traffic Engineer.
Many elected officials do not realize that there are National guidelines for the installation of Traffic Control Devices. The Manual On Uniform Traffic Control Devices (MUTCD) gives Transportation Engineers the uniform standards to safely assist motorists as they travel. It defines a series of uniform Traffic Control Devices (Signals, Signs and Pavement Markings) which are clear in their messages as applied on the nation’s roadway system.
The March 1990 issue of “Public Roads” magazine, published by the U.S. Department of Transportation, contained an article on “Motorist Compliance With Standard Traffic Control Devices.” The article examined the following forms of motorist non-compliance:
“Not coming to a full stop at STOP signs
“Failing to yield right of way to pedestrians
“Ignoring active railroad crossing devices
“Making illegal turns
“Using lanes improperly
“Violating traffic signal indications
“Driving too fast through work zones
“Encroaching on centerlines
“Violating passing zone restrictions
The behavioral studies collected compliance and other data at a large number of typical sites over extended periods of time. In the process, hundreds of thousands of motorists were observed. The clear conclusion was that motorist non-compliance is a problem.
One of the recommendations in the US DOT article was: “To ensure that the motoring public maintains a healthy respect for TCD’s, traffic professionals must use them prudently. Through concerted efforts of the nature outlined above (Engineering, Enforcement and Education), the safety and efficiency of our streets and highways can be maximized. ”
There’s no question that it’s easy to second guess Traffic Engineers, after all we’ve got a driver’s license, but when it comes to putting my life in the trust of someone else I want the trained professional rather than the armchair engineer any day.