More traffic nudges please, says a reader

Reader Francis King wrote to say Nudge could’ve included some more traffic examples.

There are exactly two ways of managing traffic – the heroic and difficult way, and the thoughtful and easy way. To restrain the speed of the cars, it is possible to use a speed camera. Alternatively, though it is possible to use a vehicle-actuated sign, which flashes up the speed limit if the next car is going too fast. Both have the same effect, yet one doesn’t involve fining car drivers, and ultimately taking their car license off them.

Even more than that, it is possible to create the illusion that the road narrows, but putting hedges along the road side, by hashing out part of the road surface, by using dragon’s teeth, or by putting up a gateway at the entrance to a village. A gateway, in essence is a small brick wall on either side of the road. As the road appears to narrow, so car drivers slow down, even though the road has not actually narrowed at all.

If white lines are removed from the centre of a road, this also causes traffic to slow down. Removing the footways and sharing the space between car drivers and pedestrians also causes the traffic to slow down. In both cases, this is due to the fact that traffic is no longer being given permission to drive along the road –uncertainty causes a reduction in speed. It also makes the road look better.

In Holland, most people cycle at one time or another, in the UK it is the preserve of a few. In Holland, because most people cycle, car drivers show great respect to cyclists, in the UK occasional contempt or violence. We have an international cycling team, but is doesn’t actually train in the UK, and one reason was the attitude of car drivers, when they were training on the roads.

Smile – you’re driving the speed limit

Here in the U.S., road signs that flash the driving speed of approaching cars are a common sight, in part because they operate at two percent of the cost of traffic cameras. The clunky acronym for these things are VAS (Vehicle Activated Speed) signs. In the U.K., however, these signs don’t just tell drivers their speed. They smile at cars under the limit, and frown at cars over the limit.

Hat tip to Rory Sutherland for pointing this out in a post on the Spectator blog. You can also read Rory’s earlier piece on why politicians shouldn’t be afraid to learn from marketers, who are, after all, masters of persuasion.

No, the happy chap in the picture above is not Rory. It’s Councillor Michael McCann, the depute (British spelling) leader of South Lanarkshire Council, and member of the Scottish Labour Party.

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.

Choice architecture for the road

Over at Freakonomics, Tom Vanderbilt, author of Traffic: Why We Drive the Way We Do, elaborates on transportation choice architecture.

When signs don’t work:

“Children at play” signs and the like are absolutely ineffective in changing a driver’s behavior, and studies of drivers through school zones show they were driving much faster than they remember. It’s been argued that signs allow us to basically stop thinking, and in certain places experiments have been done in which they’ve been removed, with no negative safety effects.

What behavioral economics tells us about it seems other lanes are always moving faster than ours:

But there’s a curious bias that plays out in oscillating shifts of traffic, observed by the researchers Donald Redelmeier and Robert Tibshirani, in which drivers, who are oriented towards observing things in the forward view much more than the rear, spend more time watching cars passing them than they spend watching themselves passing other cars.

Given the general findings that humans are more sensitive to losses than gains, it doesn’t seem a stretch to imagine that this sense of being passed — of the other lane being faster — would stick out in our brains. All you have to do is pick out a benchmark car in the adjoining lane to see how often we fall for this illusion. I’ve seen these cars pass well out of vision, only to find myself passing them again minutes later. Part of the reason this seesaw effect is happening in the first place is because of all the drivers ahead thought they could get a better deal, and basically ended up just shifting the equilibrium around temporarily.

And what technologies might help improve traffic choice architecture:

One technology that is quite clever and productive is the concept of “variable speed limits,” as seen on highways in England and elsewhere. Basically, if there’s a patch of congestion, it’s detected by sensors, and a new, slower speed limit is announced back “upstream.” That way, rather than having everyone drive at full speed into a traffic jam, which is neither good for safety nor traffic flow itself, the congestion shock wave is “damped.” Of course, people being people, you tend to have to have things like speed limit cameras there to make sure people go the suggested speed.