In previous post I proposed an algorithm for automated detection of speed limit violations from GPS data. Then in a later post I tested this on simulated data. Here I apply it to data which was collected by someone else during a short drive in San Francisco.
I've a general 40 kph speed limit within the city (also previously here), except on the interstate highways. This car trip didn't include any interstate highways, so it will be interesting to see how it would do with such a restriction.
Here's the speed versus time. As you can see, it was a short trip, only around 8 minutes:
It's mostly slow going, except for one stretch on Bayshore Boulevard, which is faster. That portion is generally 50 to 65 kph, Sure enough, this triggers the algorithm as speeding for a 40 kph limit. I assign a fine in dollars equal to the excess distance ahead of a "pace car" beyond the 50 meters allowed by the algorithm, at a ratio of one dollar per 100 meters. So if the car in question pulls 150 meters ahead of the "pace car" during the trip, that's a $1 fine.
Here's how the fine varies with speed limit:
At a 40 kph speed limit, the fine would be $1.74. It goes up substantially if the speed limit is lower. By 49 kph, it drops to zero. Note the car actually got up to 63.2 kph, but not long enough to trigger a speed limit violation between 49 and 63 kph.
At present, a speed fine is viewed as a big deal. You get pulled over, mailed a citation, given a big fine with additional fees, and possibly waste time in court defending yourself. With this system, there would be none of that. You'd get notified of a fine, and you (the registered owner of the car) would pay it by 30 days or whatever. The fine could be big or small. But acceptance of the responsibility to pay assessed fines would be part of receiving the privilege of driving a car. If you don't pay your fines accrued for your car(s), your driving privileges are suspended until you do.
This was just a short trip, so fines tend to be small. But the speed was quite modest over the majority of the drive. The goal here is to eliminate the uncertainty. If you speed to a certain threshold, you'll pay. Such a system would substantially slow the prevailing traffic speed, both increasing safety and reducing congestion. It would make getting around, by foot, bike, or even car safer and easier.
I can't simulate the advantages of reduced speed on traffic congestion here, but I can calculate, at the same level of congestion, how much longer the trip would have taken with a 40 kph speed limit cap. That's 24.8 seconds, taking the trip time from 8:36 to 9:00.8. In the spectrum of factors which contribute to delays in getting to a destination, that's a very small number, and it wouldn't take much improvement in traffic smoothness to take it to zero.