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I keep hearing here and there that cyclists should obey the rules of the road. Usually after someone nearly missed creaming one with their car at an intersection. The rules that cyclists follow are not exactly the same as the rules that traffic follows, and here’s how they differ most dramatically.

For a car in traffic, the object is avoiding collisions. Every left turn is taken after a carefully considered calculation of the velocity and distance of oncoming cars, every lane change is taken after a survey of the cars in the next lane, and even the next lane beyond that. Every right turn from a local road onto an arterial is taken after a similar calculus of distance and velocity.

The dashed stripes between the lanes, 40 feet each, or half a second of average traffic travel speed, help drivers of vehicles estimate that time to collision. We may not know or even notice the distance, but the regular beat of those stripes tells us things about those possible collisions that a solid line would not. Similarly, a traffic light or turn signal tells us that we can be assured safe passage through an intersection, as long as we obey the light. The yellow light was developed in the 1920s to tell us when to hurry up and get through the intersection, and that’s exactly what we do in traffic. Stop signs are all there for traffic to consider the other two to four directions that could cost us our money, our health and our lives should there be a collision. We’ve internalized that the red octagon in place since the 1940s means “STOP”. And we stop because it is in our interests. Not because of the one time we got busted by a cop for a “California Rolling Stop” decades ago.

Laws that are in our interests will be followed much more often, even religiously, than laws that are not. Avoiding collisions are in the interests of traffic. Traffic is full of things that are large, heavy and fast. The first access-controlled highway (the LIMP) in America, designed to avoid the head-on collisions racking up on the Boston Road, had a speed limit of 25 miles per hour. The parts of it that are still intact still show this design speed, with turns we wouldn’t dare take at 55 MPH, much less 72. 70 being the routine speed on the Northeast Corridor’s I-95, built 30 years after the LIMP.

While the fundamental concern of traffic is avoiding collisions, the fundamental ability of traffic is speed. This is what make congestion so frustrating for traffic. Even a Lamborghini could not top 30 MPH in a morning “rush hour”. Collision and expensive body work would be assured in the space of one of those stripes that tick off the miles on the highway. A Lambo is no greater than a Camry in congested traffic. Though the normal act of driving in traffic is sitting in a nice chair worrying about death, the frustrating act of traffic is when the rest of it gets in your way. What a tragedy to have something that could go 70 MPH confined to go 20.

The signals, signs, striping, and surfaces of the traffic ways are all designed with these concerns and speeds in mind. Though the width of lanes is designed to handle the peak speed, the number of lanes are there to handle the peak traffic. The signs and signals are designed to be seen for at least five second before drivers get there, so they can respond appropriately. Much of the day, much of the space, and much of the time, the road is unoccupied. Not nearly as much as the width of the highway would seem to allow, anyway.

And that’s where bikers and walkers want to cross the road. While a collision is definitely a worry for these people, they have much different concerns and abilities. A driver in traffic burns 5 calories a mile piloting the car, bikers and walkers burn dozens, and more on hills. Finding the most expeditious route is a matter of energy efficiency and time management. Walkers want to get where they are going, and if they can see that across a lonely highway without a hammer in sight they will cross that road instead of schlepping up to the nearest intersection, and waiting for the signal to change. Bikers worked hard for the momentum they have, and will scan any intersection they can to see if traffic is coming through. If not, then they go as fast as possible.

I’m not excusing jaywalking or flaunting intersection signage. Those regulations are there for the safety of traffic, walkers, and bikers alike. But those regulations and signs are designed and built at the scale of traffic, and are a poor fit for the needs of walkers sand bikers. People in traffic should be humble to that, even as they curse the biker that just darted through that intersection.


This of course, is a different issue with biking, one which I’ll write about soon.