CopRadar Blog

Prove a Redlight Camera is for Safety or a Dangerous form of Taxation

2011-08-19T17:00:00.008-05:00

The first step to determine if a Redlight Camera is for money is to answer the question; “Does the traffic light force drivers that just happen to be in the wrong spot (worse case) when light changes yellow to brake safety (worse spot at worse time)? If the answer is safe braking for worse case the camera is probably for safety. If the answer is unsafe or even dangerous worse case braking the camera is strictly a source of money (a dangerous tax) that goes to cities or states and equipment suppliers (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 It gets worse, many jurisdictions use outdated driver reaction times (some established over half a century ago) when determining yellow duration, resulting in short yellow light times and unsafe worse case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 (widen, 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 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”,
driver reaction time.

Knowing just these 5 factors a signal light’s worse case braking (and safety) can be subjectively 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 solved to get worse case braking. Once worse case deceleration is established an intersection’s safety can be subjectively determined and braking compared.

light
moderate
hard
driver maximum
dangerous
vehicle maximum

“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).

Online Calculator:

Compute Driver Braking

Police Radar Handbook Editions

2011-08-06T00:01:00.001-05:00

Print and eBook (Kindle) editions of the "Police Traffic SPEED RADAR Handbook" Web site (CopRadar.com) are now available. The print edition contains over 200 pages, all editions have over 80 illustrations / diagrams / graphs and 50 tables (see Preview Edition).

Purchase Online:
- Print Edition ($ 29.99 + shipping)
- eBook Kindle Edition ($ 9.99)
- Web Site Password ($ 9.95)

Available at Amazon and better book stores.

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How To Safety Rate Red Light Cameras

2011-08-05T00:01:00.001-05:00

Rate Stoplights by Driver Braking

Many communities use red light cameras as a revenue source, then claim it is for safety. Some places go so far as to shorten the yellow duration forcing more drivers to run the light (more revenue, less safety and harder braking). To make matters worse many states use an unrealistic (fast) driver reaction time to calculate yellow light duration.

A way to safety rate a traffic signal (including red light cameras) is to determine potential driver maximum braking . Using a realistic driver reaction time, a realistic (objective and predictable) braking number can be determined. Using a braking "g's" scale (deceleration compared to acceleration due to gravity), braking g's can be used to determine (braking) safety and comparing other stoplights.

EXAMPLE
Speed Limit: 35 mph
Road Grade: 0 %
Stop-Clear: 10 feet
Yellow Light: 4.0 sec
BRAKING* = 0.53 g’s / UNSAFE (vehicle max 0.47-0.62 g’s)
* Based on Driver Reaction Time of 2.3 seconds.

“How To Safety Rate Red Light Cameras” explains how to determine braking g's using speed limit, yellow light duration, road grade (incline), and stop bar to clear point (usually intersection) distance. Includes a discussion of factors involved, mathematical model and proof, equations, and braking scale levels. Lookup tables (English and Metric) provided for quickly estimating braking g's. Are Stoplights in your community safe -- this book will show you how to objectively and clearly rate a stoplight. See Web Site edition at CopRadar.com/redlight.

Purchase Online:
Book Edition ($ 9.95 + shipping)
eBook Kindle Edition ($ 3.99)

Also available at Amazon.

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