In 2013 Laurie Jarlstrom received a ticket for moving through a red light, while conducting a right turn. Her husband Mats is an electrical engineer originally from Sweden, and the couple now lives in Beaverton, Oregon. Being an engineer with a nuisance that seemed avoidable, Mats began to study how traffic lights work and the reasoning behind the process. Using the Institute of Transportation Engineers as a base, he found the general formula for the Change Period of a yellow light, and the variables that affected that period.
Breaking the formula into its three components, Jarlstrom found that the perception and reaction time of the driver, the deceleration time of the vehicle and the time for the vehicle to clear the intersection all came into play. This was further simplified into total stopping time, and clearance time. This formula only accounts for the driver to make two decisions, moving forward through the intersection or stopping. The additional variation occurring when a driver makes a right or left turn was not present in the equation.
Jarlstrom wrote a paper (An Investigation of the ITE Formula and Its Use) for the Institute of Transportation Engineers, using the ITE formula and then deriving his own formula and testing his work against a number of situations. Vehicle traveling at constant velocity, vehicle traveling with constant acceleration, vehicle traveling with a stopping motion, and typical input values were all studied. The variation between Jarlstrom’s formula and the ITE formula is the deceleration term, and this condition is highlighted even more when a vehicle is slowing to turn right but proceeding through the light.
Mats has been in the news the last few weeks because he pointed this issue out to Oregon State Board of Examiners for Engineering and Land Surveying, and they issued a $500 fine for practicing engineering without a license. I’ve seen this issue framed in terms of free speech and who is able to call themselves an engineer or offer input to the government. But to me this is a better opportunity to really think about what it means for someone to be an engineer. Engineers should see a problem, do research into the system and circumstances of the problem, perform analysis and simulation, and then offer a solution. My simplistic goal for engineers is always to make the world a better place, and this is what Jarlstrom was attempting to do both by studying the way that lights are timed and presenting his information to the Institute of Transportation Engineers.
(video courtesy of the Institute for Justice)