Want slower traffic? Slow yourself down

Everyone hates speeders.

At least, until they find themselves late for the departing ferry. Then those pesky speed limits tend to be “forgotten” in the mad race to Winslow, and our otherwise pious drivers pray that local patrol officers happen to be cruising another part of the island.

So we’re not sure there’s a cure-all for our collective lack of delicacy with the accelerator pedal unless and until, perish the thought, there’s a bridge to Seattle. Maybe not even then.

This week, a divided City Council bowed to lobbying by westside island residents and lowered the speed limit on Miller Road – the main arterial from Day Road to the south end of the island – to 35 miles per hour. This, over the general objections of city engineers, and despite police analysis that shows Miller is not a high-accident corridor.

We concede that there is an intuitive appeal to lowering speed limits, evidenced by similar calls from other neighborhoods. But does changing the signs really make a difference?

By way of background, roadway speed designations are

traditionally established by what traffic engineers refer to as the “85th percentile rule,” that is, the speed at or below which 85 percent of drivers will instinctively travel in a given location under normal conditions. The assumption is that most drivers constantly assess such factors as lane width and the presence of cross streets and driveways, then gravitate to the velocity at which they feel comfortable and safe. This standard, as one highway department notes in its literature, offers several advantages: it invites compliance by conforming to the behavior of the majority, and gives a clear reminder of prudent speeds to violators, all the while giving police an effective enforcement tool and minimizing complaints about “speed traps” that follow unreasonable regulation.

The corollary argument is that artificially low speed limits criminalize the behavior of the majority of motorists – good drivers and bad ones alike – and actually pique contempt for the law. They may also increase the accident risk for non-motorized travelers, by suggesting that traffic speeds in an area are lower than they really are.

Studies of rural roadways published by the Federal Highway Administration are instructive. Data compiled in various states over a period of decades suggests that lowering speed limits by 5-10 miles per hour has little effect on the behavior of motorists.

Maybe Bainbridge Island will buck that trend, and speeds will decrease appreciably on Miller Road. Maybe the implicit goal is just to see “the other guy” get more tickets, although we’re not sure our police department even has the resources or inclination to beef up enforcement in that area.

But it does seem that if we begin changing speed limits

arbitrarily, based not on science but on which neighborhoods complain the loudest, we are moving traffic management from the objective sphere of engineering and into the capricious realm of politics. That doesn’t seem like a very good direction.

Sure, the city can post all the signs it wants. But like it or not,

the traffic studies suggest that driving slower is, ultimately, a personal decision.

Solve that one, and you’ll really have something.

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