Why Cyclists Blow Through Stop Signs: It's Physics

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A red light for bikes to stop in an urban setting.

Michele Ursi / Getty Images

About 30 years ago, residents on Toronto's Palmerston Avenue were complaining about cars racing up and down the street, using it as a way to avoid the nearby busy arterial Bathurst Street. That part of Toronto is laid out with the streets predominantly east-west, and had two way stops at the end of the streets meeting Palmerston. The local alderman Ying Hope, a notorious pothole fixer, lobbied to put stop signs on the north-south Palmerston as well, to slow down traffic enough that perhaps drivers would not bother to use it and would stay on Bathurst. Traffic planners were appalled; two way stops worked perfectly well at regulating right of way, which was the purpose of signage. Four way stops waste gas and might cause more accidents because right of way was not as clear.

But the alderman got his way, and the street became known affectionately as the "Ying Hope Memorial Speedway." The cars stopped using it because stopping every 266 feet was a real pain, and slower than driving on the arterial. Soon everyone wanted four way stops to slow traffic in their neighbourhoods and now, they are almost universal.

Why am I telling this story? Because bikes are in the news in Toronto in the aftermath of the death of Jenna Morrison, and the letters to the editor sections are full of ones like today's:

If we need to share the road, then we need to equally follow the rules of the road as stated in the Highway Traffic Act. Cyclists need to stop flaunting their ability to run stop signs.

When you read the comments in recent posts, just about every one is complaining about bikes and stop signs. But the fact of the matter is, those stop signs are there to regulate speed, not right of way; two way stops actually do a better job of that. And bikes have a hard time beating the speed limit.
In neighbouring city Hamilton, Ontario, the cycling committee proposed changes to the Highway Traffic Act to permit "Idaho Stops". Adrian Duyzer explains in Raise the Hammer: that "An 'Idaho stop' is so-called because of a 1982 law passed in Idaho that permits, in essence, cyclists to treat stop signs like yield signs." The law requires cyclists "to slow down to a reasonable speed and, if required for safety, stop when they come to a stop sign" and "yield the right-of-way to any vehicle in the intersection or approaching on another highway." That seems reasonable, and frankly, that is what I and most other responsible cyclists do. There is a reason: Physics.

Duyzer points to an article by Professor of Physics Joel Fajans at the University of California, Berkeley, and Melanie Curry of Access, titled Why Cyclists Hate Stop Signs. They write:

Take a simple stop sign. For a car driver, a stop sign is a minor inconvenience, merely requiring the driver to shift his foot from gas pedal to brake, perhaps change gears, and, of course, slow down. These annoyances may induce drivers to choose faster routes without stop signs, leaving the stop-signed roads emptier for cyclists. Consequently streets with many stop signs are safer for bicycle riders because they have less traffic. However, a route lined with stop signs is not necessarily desirable for cyclists. While car drivers simply sigh at the delay, bicyclists have a whole lot more at stake when they reach a stop sign.
Bicyclists can work only so hard. The average commuting rider is unlikely to produce more than 100 watts of propulsion power, or about what it takes to power a reading lamp. At 100 watts, the average cyclist can travel about 12.5 miles per hour on the level.... Even if a commuter cyclist could produce more than a 100 watts, she is unlikely to do so because this would force her to sweat heavily, which is a problem for any cyclist without a place to shower at work. With only 100 watts’ worth (compared to 100,000 watts generated by a 150-horsepower car engine), bicyclists must husband their power. Accelerating from stops is strenuous, particularly since most cyclists feel a compulsion to regain their former speed quickly. They also have to pedal hard to get the bike moving forward fast enough to avoid falling down while rapidly upshifting to get back up to speed.
For example, on a street with a stop sign every 300 feet, calculations predict that the average speed of a 150-pound rider putting out 100 watts of power will diminish by about forty percent. If the bicyclist wants to maintain her average speed of 12.5 mph while still coming to a complete stop at each sign, she has to increase her output power to almost 500 watts. This is well beyond the ability of all but the most fit cyclists.

Of course, the article drew the usual response from readers:

And I am sorry, but this is CRAP. If cyclists want to be treated with the same respect on the road as every other vehicle - both by drivers and by legislators - they they need to obey the traffic laws. Period.

And I am sorry, but for this particular issue, the law is an ass. It defies logic and physics. I wish the traffic engineers who put these signs in would acknowledge this, and I wish the papers would stop printing these stupid repetitive letters.