Red Light Robber

Yellow Light Flaw in One Page

California MUTCD 2014 Rev 3 Yellow Change Interval Equation

The California MUTCD's Table 4D-102 has a derivation of the yellow change interval equation from the "detector setback" equation. It is the only State MUTCD where one sees the origin of the equation. When you see the origin of the equation, it is easier to see when the equation fails.

The CA MUTCD uses the term "detector setback distance". This distance has the same mathematical formulation as the stopping distance. The stopping distance, when referring to yellow lights, is also called the critical distance.

For any person who has taken an introductory physics class, it should be obvious where the "T" equation goes wrong. The "T" equation defines "V" in the numerator as the same "V" as that in the denominator. This is incorrect. The "V"s are not the same.

This is correct: The "V" in the numerator is the initial speed at the detector setback distance upstream from the intersection. On the other hand, "V" in the denominator is the average speed of the vehicle between the detector setback distance and the limit line.

"V" being the same in the numerator and denominator is a special case. The special case only happens when a vehicle does not change speed as it travels from the detector setback distance to the intersection. Such unchanging speed is typical of unimpeded vehicles going straight through the intersection. But such unchanging speed is atypical for turning movements or movements where business entrances are close by the intersection. Turning movements and movements where vehicles pause for other vehicles entering and egressing from businesses, require drivers to change V while traversing the critical distance.

Example. Consider turning movements where S is the speed limit and 20 mph is the speed to which the vehicle decelerates into the intersection. Here "V" in the numerator is S while "V" in the denominator = (S + 20) / 2. Plugging in the latter "V", the correct "V", results in a "T" several seconds longer than the "T" in the CA MUTCD. Traffic engineers typically make the "V" shorter for turning vehicles than straight-through while it should be longer. The result is in the crash and RLR data. Crashes and RLRs are 15x higher for turning lanes than for straight-through lanes.

(As an aside, the detector setback distance is not the distance an advance or dilemma zone detector should be placed. This is a math error too.)

California MUTCD 2014 Rev 3

Transportation and Traffic Engineering Handbook, 1982

These two pages contain the engineeers' operational directions for the yellow light. Read the bottom of the first column and the top of the second column. Note that engineers tell a driver that he must not decelerate on route to the intersection and that sometimes the driver must accelerate to beat the light.

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

This paper explains the physical meaning of the yellow change interval formula, its history and how today's traffic engineers all over the world misapply the formula and force drivers to run red lights.

California Commercial Driver Manual

California Driver Handbook

California Government Code 11340

Vehicle Code 21400

This law states the California must conform to the California MUTCD.

California Professional Engineers Act

The statutory requirement for a professional engineer is to know the science and apply it in his work (section 6701). The traffic engineer does not know the physics of this own yellow light formula and forces drivers to run red lights. He therefore violates section 6704a and is forbidden to practice engineering.

Red-Light Cameras Have Not Reduced Crashes

Mayors, city councilmen, city managers and police chiefs in California have officially recorded that red-light cameras have not reduced crashes in their cities.

Safer Streets L.A.

Highway Robbery