What Cyclists Wish Drivers Knew Number 2: The Math of Safe Passage

As a road cyclist who travels country roads and city streets almost every time I leave the house, I'm justifiably concerned about impatient drivers who endanger me, not to mention themselves, because they're determind to get on down the road. So what's your hurry, folks? Is the time you save by zipping past eighteen inches from my elbow (instead of waiting to pass safely) worth it? I thought this might be a good time to take a look at some simple math to see how much time you save by your maneuver.

Let's assume driver and cyclist are on a city street with a speed limit of 35 MPH. The cyclist is moving at 15 MPH (a reasonable speed) and the driver is -- naturally -- five MPH over the speed limit at 40 MPH. Here's our scenario:

1. The bicycle is moving at 22 feet per second (fps).
2. The car is moving at about 59 fps.
3. The driver waits 30 seconds before he's able to pass safely.

How much time does that driver "lose"? Several minutes? More? Less? Let's take a look at the math¹:

4. At 15MPH, the bicycle and car move 22 x 30 = 660 feet
5. A car moving 40MPH would move 59 x 30 = 1770 feet
6. After passing, the car is 1770 - 660 = 1110 feet short of the "unimpeded" position.

More than 1100 feet may seem like a lot, but it's not: at 40 MPH, it will take the driver 1110 / 59 = 18.6 seconds to cover that distance. If the driver were obeying the speed limit, the added time would be 17.1 seconds. That doesn't even account for the fact that drivers must only rarely wait thirty seconds to get a safe passage window. Do you think that saving eighteen seconds is worth endangering someone else's life? I don't.

¹ Yes, the real math is more complex, because the changes in velocity aren't instantaneous. Face facts, though: if many people are flummoxed by word problems that require simple algebra; how are they going to react to calculus?

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