Anointed Pillars

My daily commute often includes coming to a complete stop from 40 mph due to a pedestrian crosswalk (with full stoplight) on Bridle Crest Trail. The road has 2 lanes in each direction and is far enough from major intersections such that there are regular opportunities to cross without needing to manually trigger the light.

Image Credit: © 2013 Google

Each time the stoplight is triggered, approximately 20 vehicles must come to a full stop on either side of the road (40 vehicles total). Assuming a typical weight of 3,200 lb, the minimum kinetic energy lost and expended to regain the speed limit is 18.6 MJ(*). Given that a gallon of gasoline contains about 130 MJ, each crossing ‘consumes’ 14.3% of a gallon. At $3.85/gal, the crossing costs society $0.551 or about $0.014 per motor vehicle.

(*)This is conservative as starting from a stop is the least efficient mode of operation for a typical motor vehicle, and more energy must be expended to regain what was lost. Here I have simply doubled the lost kinetic energy. Furthermore, I am not including gasoline consumed at idle for the duration of the crossing..

Assuming average vehicle mileage is 20 mpg, each similar crossing translates to 2.86 miles of motor vehicle travel. Ironically, if the crossing is used by a pedestrian or bicyclist who otherwise drives a Prius (as their behavior may indicate), this increases to 6.44 miles (assuming 45 mpg as their specific opportunity cost).

Therefore, we can say that if a few people cause a sufficiently large number of motor vehicles to fully stop frequently enough  (in this case once every 3 miles), society would be better served by that person using a motor vehicle.

Source for energy content of gasoline: The Impact of Stopping on Fuel Consumption, Victor Miller (Nov 19, 2011).