Saturday, May 17, 2014

A physics-based solution to the Idaho Stop

How about we take a physics-based approach to the Idaho Stop controversy? Recall that the Idaho Stop only applies IF THERE IS NO ONE ELSE NEAR THE INTERSECTION who has the right of way.

Since the amount of damage inflicted upon others is proportional to the momentum, let's set a small--but non-zero--maximum limit to the minimum momentum of travelers approaching intersections.

1 mph = 0.45 meters/second

For example, let's use some typical masses:
  • Pedestrian = 70 kg
  • Bicycle+rider = 100 kg
  • Automobile+driver = 2000 kg
Suppose the maximum momentum of intersection approach is set to 100 kg-meters/second.  Then:
  • a pedestrian needs to slow down to 1.4 m/s or about 3 mph when approaching a stop sign.
  • a bicylist needs to slows down to 1 m/s or about 2 mph.
  • an automobile needs to slow down to 0.05 m/s or about 0.1 mph.
A quick survey of cars at the nearest stop sign to my home shows that most cars exceed this threshold by more than a factor of 10. When commuting or running errands in the city, I bike 5-15 mph (hills!) so slowing to 2 mph wouldn't be burdensome. Most city pedestrians walk at 3-4 mph; they barely need only slow slightly for stop signs IF NO ONE ELSE IS NEAR THE INTERSECTION.

If others are near the intersection, then the normal rules of total stop (zero momentum) and right of way assignment apply.

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