[Editor's note: The following was sent to us by Donald Sawicki of Copradar.com, a site where Mr Sawicki offers insight and literature on radar and red light camera safety issues to victims, defendants and legal professionals.]
The first step towards determining if a red light camera exists to make money is to answer the question: Does the traffic light force drivers that just happen to be in the wrong spot (worst case) when the light changes yellow to brake safely (worst spot at worst time)? If the answer is “safe braking for worst case” the camera probably exists for legitimate reasons of safety. If the yellow light forces unsafe or even dangerous worst case braking, the camera is strictly a source of money (a dangerous tax) that goes to cities or states and equipment suppliers (which typically split the booty). To catch (trap, trick, hook or crook) more redlight runners some municipalities shorten the yellow time forcing drivers (even NEAR worse case distance) to run the light. It gets worse: many jurisdictions use outdated driver reaction times (some established over half a century ago) when determining yellow duration, resulting in short yellow light times and unsafe worse case braking.
There are a number of reasons a large number of stoplights have too short yellow times’. One reason is when stoplights (3 color system patented in 1922) were introduced in the first half of the 20th century (when vacuum tubes were new) reaction times were “estimated” to be 1 to 1.5 seconds — stilled widely used in the early 21st century. In 1999 a detailed controlled study (on a controlled track and in a driving simulator using licensed drivers with various skill levels) determined average driver reaction time to be 2.3 seconds. California uses 2.5 seconds, the National Safety Council (NSC) and Great Britain use 3.0 seconds.
Another reason for short yellow times is many intersections that have been improved and changed (widened, crosswalks added, lane usage changed, etc.), some multiple times, were not reevaluated for yellow duration (an oversight or mistake). Another common error is a speed limit is increased but yellow times stay the same (and now too short for the increased speed).
A second more or less can make a huge difference between safe and dangerous braking. At the beginning of 2011 the Missouri Department of Transportation (MoDot) started reevaluating and adjusting all state controlled traffic light yellow times. MoDot is serious about public safety. So far MoDot has increased yellow duration’s ranging from 0.3 seconds to 1.3 seconds. This summer one ot the traffic lights reevaluated and yellow time increased had a redlight camera. Red light runners dwindled to a trickle from over 1500 per month to less than 20 per month, a 99% DROP!
A traffic light’s safety can be subjectively established using a few measurements and a little mathematics. Only 5 parameters are needed to determine worse case braking; speed limit, road grade, yellow light duration, distance from “stopline” to “in the clear”, and driver reaction time. Knowing just these 5 factors a signal light’s worse case braking (and safety) can be objectively established and degree (or lack) of safety.
Speed limits are usually posted, road grade is 0 for flat level terrain. Yellow light duration is best measured with a video camera and counting yellow light frames. Stop to clear distance varies with intersection and state. In many states the official “Rules of the Road” cite something to the effect “When the red light appears, you may not enter the intersection”*, setting the clear line at the cross-street curb line. *From Illinois Rules of the Road.
The mathematical formula for traffic light timing is widely published (the Institute of Transportation Engineers – ITE for example). The formula calculates yellow light time, by rearranging the formula deceleration can be obtained to get worse case braking. Once worse case deceleration is established an intersection’s safety can be subjectively determined and compared (light, moderate, hard, driver maximum, dangerous or vehicle maximum braking).
“How to Safety Rate Redlight Cameras” discusses in detail the parameters (and formulas) involved, and has an online calculator that computes braking action given speed, road grade, stop-clear distance, yellow duration, and (a safe for EVERYONE) driver reaction time (2.3 seconds minimum recommended).