ITE Releases New Yellow Change Interval Practice

ITE Journal March 2020 ITE Signal Guidelines

The Institute of Transportation Engineers (ITE) is a private organization that establishes the practices Departments of Transportation use to set the length of the yellow light. In 1965, ITE introduced a practice that does not conform to the laws of physics. The bad physics causes every driver in common scenarios to inadvertently run red lights. Over 90% of red-light running, as data reveals, is caused by ITE's errors and omissions. The red-light camera industry simply profits from ITE's practice.

After 20 years of confrontation, on March 1, 2020, ITE made a great stride to correct its bad physics. ITE adopted the mathematical works of Dr. Alexei Maradudin (1960-2018), Dr. Chiu Liu (2002), Brian Ceccarelli (2010), Jay Beeber (2012) and Mats Järlström (2013).

Beeber Maradudin Jarlstrom

Jay Beeber, Alexei Maradudin and Mats Järlström

The ITE Journal contains an article by Jay Beeber. Beeber correctly explains Järlström's extended kinematic equation. Beeber's explanation is 100% correct not only about Järlström's equation, but also about the underlying physics principles of what a yellow light is supposed to be. Beeber also includes brief treatises on the requirements for engineering tolerances for law enforcement and the correct application of physics dynamics for the road-grade adjustment. ITE's March 2020 Journal is historic because it is the first time an official ITE publication gets the math of the yellow light right.

You may download the Excel spreadsheet to compute the new official yellow change intervals. I included the yellow change intervals for commercial vehicles so that one can see the range of valid yellow change intervals which accommodate all allowed drivers on the road. ITE now officially acknowledges a valid range of perception-reaction time and deceleration values, not just the one average value for passenger sedans on dry pavement. ITE does make a strong statement that zero-tolerance by red-light camera firms is bad.

Unfortunately, at the moment, the Guidelines document gets it somewhat wrong. Traffic engineers use the Guidelines, not the Journal, to compute yellow light durations. One can read the ITE Guidelines and construe use cases that undermine the physics. We are currently working to have ITE officially correct the math and the verbage.

The world's Departments of Transportation do not have to adopt ITE's practices. ITE has no authority.

Physics and Math

The Problem of the Amber Signal Light in Traffic Flow

The Problem of the Amber Signal Light in Traffic Flow; Gazis, Herman, Maradudin

Gazis, Herman and Maradudin (GHM) co-authored this paper in 1959. In 1965 ITE miscopied this paper's equation 9 into its Traffic Engineering Handbook. By omitting GHM's "Analytical Considerations", ITE has been instructing traffic engineers to abuse this formula for over 50 years.

The Problem of the Amber Signal Light in Traffic Flow

Determination of Left-Turn Yellow Change and Red Clearance Interval, Liu

The American Society of Civil Engineers (ASCE) Journal of Transportation Engineering published Dr. Chiu Liu's paper in 2002. This paper is the follow-up work to Gazis, Herman and Maradudin. Dr. Chiu Liu's formula computes the minimum yellow duration which allows all traffic to move legally. Chiu's formula is equation 13 on page 454.

The beginning of the paper states explicitly that the turn lane yellows must be longer than the straight-through. The new ITE guidelines say that Liu's turn lane yellows will be shorter than the straight-through.

Extended Kinematic Equation Explanation

Järlström's Extended Kinematic Equation Explanation, Beeber, ITE Journal

Mats Järlström's equation is for both right and left turning. This article appears in the March 2020 issue of the ITE Journal. It is a perfect explanation of both Järlström's equation, the purpose of the yellow light, and the general principles of tolerances and when it is correct to use the grade adjustment.

Extended Kinematic Equation, Jarlstrom

Extended Kinematic Equation, Järlström

This is Mats Järlström's technical paper describing his turning equation. The GPS/Race-Logic data Järlström uses profiles a right-turning vehicle's approach to the intersection. It is beautiful. One can visually compare reality with his equation of physics.

Järlström's equation models a different type of vehicle approach than Liu's equation. Yet both equations are correct. The equations yield similar values. Using either equation is good practice.

Järlström's equation has the added benefit of capping the yellow change interval to the stopping time--which would be the time it takes a driver to make a U turn.


Yellow Change and All-Red Clearance Equations of Physics, Ceccarelli

This paper lists the physics equations which allow different types of traffic movements to legally enter an intersection.

Equation 14 differs from Liu and Järlström. Equation 14 models the velocity/distance profile for the fastest turning approach into the intersection. Liu's and Järlström's equation models the profile for the slowest turning approach.

Derivation of the ITE Yellow Change Interval Formula

Derivation of the ITE Yellow Change Interval Formula, Ceccarelli

This paper shows the mathematical steps to derive the yellow change interval formula, both the ITE through-movement and Liu's equation from F= ma--Newton's second law of motion. The paper describes the physics and the assumptions.

Uncertainty in the Yellow Change Interval

Uncertainty in the Yellow Change Interval, Ceccarelli

In the presence of the misapplication of stochastic methods, like using the average perception/reaction time or 50th percentile deceleration, one must compute tolerances for the yellow change intervals so that law enforcement does not punish drivers entering the intersection on red within the uncertainty of engineering calculation. The method to do this is called error propagation. This paper describes the mathematical technique of propagating errors. Typical tolerances range from about +/- 2.0 to 3.5 seconds.

It is the responsibility of the traffic engineers, not the red-light camera industry, to compute the tolerance. The red-light camera grace period must be at least the tolerance.

Five Major Engineering Errors and Omissions

The Yellow Change Interval: Five Major Engineering Errors and Omissions, Ceccarelli

This paper explains the five major ways traffic engineers as a profession misapply the physical and mathematical sciences thus putting in harm’s way the life, health and property of the public.


Contrast between Practice and What is Required

Yellow Time: Contrast between Practice and What is Required, Ceccarelli

How much yellow time do reasonably-perceptive drivers need? Do commercial vehicle drivers need more time? This chart reveals how traffic engineers systematically short the yellow for reasonably-perceptive drivers and for various of types of vehicles.

(Click here for North Carolina specific.)

Misapplied Physics Profits Red Light Camera Companies

Misapplied Physics in the International Standards that Set Yellow Light Durations Forces Drivers to Run Red Lights, Ceccarelli

This paper describes the formula, what it does and how today's traffic engineers misapply it. This paper also presents red light camera citation data showing how minor changes in yellow light durations dramatically and permanently affect red light running counts.

Maradudin's Letter to ITE Condemning ITE for Misapplying His Formula

Letter Condemning ITE for Misapplying His Formula, Maradudin

This is a letter (July 2015) from Professor Alexei Maradudin, the last surviving inventor of the yellow change interval formula. In an upcoming yellow light guideline which ITE is about to publish (called the RP), ITE misquotes Maradudin. Maradudin does not take kindly to that. Maradudin does not like ITE misapplying his formula to turning motions and to any motions impeded within the critical distance. Maradudin does not like that ITE intentionally and knowingly forces drivers to run red lights by establishing a standard which sets the speed used in the formula to values less than the posted speed limit.

Yellow Change Interval Dos and Donts

Dos and Don'ts of the Yellow Change Interval Formula, Maradudin

This is a letter (July 2013) from Professor Alexei Maradudin, the last surviving inventor of the ITE yellow change interval formula. Every Department of Transportation in the world does the don'ts which cause drivers to inadvertently run red lights.

Blinded By The Truth

Does the Multibillion-Dollar Red Light Camera Sector Owe Its Existence - and Profits - to Traffic Engineers' Misapplication of the Yellow Change Interval Formula?, Ceccarelli, Shovlin

Traffic Technology International, a London-based journal, published this cover story about red light cameras exploiting the faulty ITE equation in its October/November 2013 issue. This story summarizes much of the literature on this web site.


Animation Slow Down at Critical Distance Animation Left Turn Slow Down at Line Animation Right Turn Animation Slow to Turn

Animations Illustrating the Problem by Johnnie Hennings, P.E., Accident Reconstruction Analysis, Inc., Raleigh.

The animations are to scale and true to the laws of physics.

In the animations you will see the "critical distance". The critical distance line marks the closest point to the intersection where the driver can still stop safely and comfortably. The line is the point of no return. By federal guideline the amount of time the light is yellow equals the time it takes the driver to traverse the critical distance on the precondition that he travels at the speed limit. You see this fact play out watching the straight-through unimpeded drivers in the following videos. But notice how the yellow will be too short for turning and impeded drivers.

  1. The first animation has the light turning yellow the moment after the left-turning driver crosses the critical distance line. The traffic engineer forces the turning driver to run a red light.

  2. The second animation has the light turning yellow the moment the left-turning driver applies his brakes in order to slow down to prepare for his turn. The traffic engineer forces the turning driver to run a red light.

  3. The third animation shows a right-turning driver. He has the same problem as the left-turning driver. The traffic engineer forces the turning driver to run a red light.

  4. The fourth animation shows a straight-through driver who has to slow down to avoid the car that emerged from a business. The traffic engineer forces the impeded driver to run a red light.

Most States implement a shorter turn lane yellows than through-movement lanes. This demonstrates that traffic engineers do not understand the kinematics of the ITE yellow change interval formula. A new federal guideline called NCHRP 731, formalizes the implementation of the error. One of the 731's authors is Richard Retting, the father of the red light camera industry in America.

I-Team:  Are Yellow Lights Too Short When Making Turns?

I-Team: Are Yellow Lights Too Short When Making Turns?

ABC WTVD, Channel 11, Raleigh, NC: May 5, 2014.

This newscast includes an interview with Dr. Alexei Maradudin, the inventor of the yellow change interval formula. Maradudin rebukes DOTs all over America for their misapplication of physics.

Kevin Lacy, a spokesman for the NCDOT, responded to ABC. Lacy claims that there is no deterministic equation which models all traffic. Lacy is wrong. The deterministic equation not only models all traffic, but all objects in the universe. It is a = v/t, eq. 41 here, of Newton's second law of motion. The equation for turning traffic is eq. 13 here. The red light camera empirical data proves that the deterministic equation is the solution. That should be expected. Everyone (other than traffic engineers) have known about this equation since 1687 when Isaac Newton discovered it.

Johnnie Hennings, P.E., an accident reconstructionist, wrote a rebuttal to Kevin Lacy's/NCDOT's letter.


Television Newscasts

Science Proves Yellow Lights too Short

I-Team: Are Yellow Lights Too Short When Making Turns?

ABC WTVD, Channel 11, Raleigh, NC: May 5, 2014.

Science Proves Yellow Lights too Short

I-Team: Raleigh Fraudulently Issuing Red Light Camera Tickets

ABC WTVD, Channel 11, Raleigh, NC: Feb 5, 2014.

Science Proves Yellow Lights too Short

Red light Camera Traps: Does Science Prove Our Yellow Lights are too Short?

"The Institute of Traffic Engineers miscopied the yellow change interval formula into its 1965 engineering handbook. Traffic engineers, the so-called experts, do not know the math and science behind their own formulas."

CBS WTKR, Channel 3, Hampton Roads, VA: February 5, 2014.

WTKR. Newport News Re-evaluates Yellow Times

Newport News Re-evaluating Yellow Light Times after NewsChannel 3 Investigation

CBS WTKR, Channel 3, Hampton Roads, VA: February 7, 2014.

WTKR - Redflex has Violation Calculator

Redflex Tells Local Cities Where to Put Cameras Based on ‘Violation Calculator’

CBS WTKR, Channel 3, Hampton Roads, VA: February 19, 2014.

WTKR proves what we suspected. Redflex knows physics too. Given the predictable failings of the ITE yellow change interval formula, Redflex wrote a violation calculator to compute exactly where the engineering failures produce the most revenue.


The Red Light Cameras of Cary, North Carolina

by Chad Vader


This is a true story. This is an account of the red light camera program that existed in the Town of Cary, North Carolina. Dr. Moley represents the real-life person Brad Hudson. Hudson came to work once a month and without looking at the videos, accused and convicted everyone of running a red light. Baby Cookieflex plays the part of Maria, an employee of Redflex. She worked at the Safelight office in Cary. If you had a problem with the ticket, the Cary police sent you to Maria or to Frank Rubino. Maria indeed said, "Aren't you happy that your $50 goes to public schools? Don't you care about children?" Until the very end of the Safelight program, Cary had spread Redflex's propaganda line to the local TV stations and the newspapers. Cary never said what percentage goes to schools. By contract, the Town of Cary paid Redflex $49.50 of every $50 for approaches which had less than 120 violations per month. That is 99%. That leaves 50 cents to the schools. The contract contained a tiered compensation clause. When the Town of Cary and the NCDOT engineers caused more than 120 drivers to run red lights per months for an approach, Cary had to pay Redflex 60%. Once Cary took out its own administrative costs, about $5.00 out of $50.00 went to the schools.