Another visual trick to nudge drivers to slow down

In Nudge, Thaler and Sunstein talk about a curve in Chicago’s Lake Shore Drive that uses a nice visual illusion to nudge drivers to slow down. Road planners in Philadelphia have been experimenting with painted illusions of speed bumps on some roads to accomplish a similar effect. From the New York Times:

The triangles are known variously as 3-D, virtual or just plain fake speed humps. They are among the latest tools in the age-old battle between drivers who exceed speed limits in residential neighborhoods and residents, law enforcement officers and government officials who want to slow them down.

Real speed humps — not to be confused with their more jarring cousins, speed bumps, a mainstay of some parking lots — are rounded mounds of traffic-calming asphalt that generally span a roadway. The virtual variety — flat pieces of plastic that are burned into the street, with the configuration of the colored lines conveying the illusion that a driver is about to cross the real thing — is less expensive ($500 each, versus $2,000), does not impede water flow and poses no threat to ambulances or other speeding emergency vehicles.

City road crews burned 10 sets of the humps into a half-mile stretch of road to tests their effects on drivers.

Before installation, Ms. Tolson said, drivers along that stretch of the two-lane road, often used as a neighborhood shortcut, were clocked averaging 38 miles per hour, 13 m.p.h. above the posted speed limit. A month later, that figure has dropped to 23 m.p.h.

Addendum: Tom Vanderbilt of How We Drive has similar thoughts to Colin. Check out Vanderbilt’s post for a bird’s eye shot of the Lake Shore Drive curve.

One of the main drawbacks is that people who live in the neighborhood or use the road regularly (and remember most crashes happen close to our homes) will become familiar with the visually confusing speed bumps. There’s other ways to tackle the problem, however. The road could be narrowed — a proven speed reducer — or, similarly, parking permitted on both sides (it’s unclear from the photo whether that’s the case). Different types of pavement treatments could be installed to break up the visual notion of the road as a straightaway. Most ambitiously, the yellow line could be removed. A number of studies have shown that, in the absence of a dividing line, speeds decrease, while distance between opposing traffic streams actually grows. The yellow line is a subtle signal to speed up — one’s territory is “safely” marked. Whether removing the line is more or less “safe” is a relative question; after all, the best safety measure for all involved, drivers and neighborhood residents, would be lower speeds.


2 Responses to “Another visual trick to nudge drivers to slow down”

  1. Colin Says:

    Won’t the effect be short-lived as motorists soon learn that it’s a trick?

  2. Philip Frankenfeld Says:

    This can be called “bump l’oeil”.

    If drivers become immune to the bumps with iterative exposure, we indeed have a situation of moral hazard.

    Moral hazard is closely linked to roads.

    On the road to ruin, with all its good intentions, moral hazard is the reprieve that repaves.

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