Archive for April 1st, 2009

A great anecdote from an article in Smithsonian (which quotes Traffic) on risk compensation:

Soon after the first gasoline-powered horseless carriages appeared on English roadways, the secretary of the national Motor Union of Great Britain and Ireland suggested that all those who owned property along the kingdom’s roadways trim their hedges to make it easier for drivers to see. In response, a retired army colonel named Willoughby Verner fired off a letter to the editor of the Times of London, which printed it on July 13, 1908.

“Before any of your readers may be induced to cut their hedges as suggested by the secretary of the Motor Union they may like to know my experience of having done so,” Verner wrote. “Four years ago I cut down the hedges and shrubs to a height of 4ft for 30 yards back from the dangerous crossing in this hamlet. The results were twofold: the following summer my garden was smothered with dust caused by fast-driven cars, and the average pace of the passing cars was considerably increased. This was bad enough, but when the culprits secured by the police pleaded that ‘it was perfectly safe to go fast’ because ‘they could see well at the corner,’ I realised that I had made a mistake.” He added that he had since let his hedges and shrubs grow back.

I couldn’t help also think of a story today about a woman killed by a reckless driver (police think he was racing, and manslaughter charges are a possibility) in San Diego.

“Route 67 between Poway Road and Ramona has been the scene of numerous fatal crashes over the years. Calls to widen the winding route have been made for some time, but transportation and highway patrol officials say the real problem isn’t with the road but with the way people drive on it… Speeding is responsible for most of the crashes, they say.”

It’s amazing how short-sighted (not seeing the forest for the, er, hedgerows) people can be in this respect; widening the road is absolutely the last thing that will reduce what seems to be a speed problem.

The long-elusive silver bullet of traffic safety, if you read this press release, has arrived in the form of the … iPhone!

From the same company that produces a “speed trap” detection application for the iPhone, thus decreasing the safety of the road both in terms of speed and distraction, comes this bold claim:

Njection.com (http://bit.ly/gJjNa) added another layer to their Speed Trap mapping system today by including traffic accidents and fatalities to enhance their data visualization system. This addition will allow drivers to see where accident black spots and problem areas are. An updated Njection Mobile iPhone application [iTunes] (http://bit.ly/4ZFmg) that allows drivers to be alerted to these high accident areas is awaiting approval from Apple.

[uh, quick interjection; a good deal of crash blackspots are at intersections, which are typically controlled by traffic lights, and sometimes, because people don't seem capable of obeying simple traffic signals, red light cameras, which your software will also sniff out — thus potentially increasing the very crash blackspot-ness! How wonderfully intregrated!]

Njection.com has acquired accident data from the National Highway Traffic Safety Administration (NHTSA - http://bit.ly/C5gpV) and global weather conditions from WeatherBug.com (http://bit.ly/uwmK2), and coupled this information with Microsoft Virtual Earth (http://maps.live.com) to produce a unique use of data visualization. This Virtual Earth mash-up not only allows users to view 5 years of accident data collected from the NHTSA based on local weather conditions but to see it in 4-hour blocks updated every hour from the current time. For example, if it is 12PM and a user selects the “4 hour history” radio button, they will be shown a history of accidents that have occurred between 11AM and 3PM based on the local weather conditions.

I realize this is a press release (regurgitated without comment by Fox Business), and not to mention this is still early days for the iPhone — every app is announced with breathtaking excitement, but most will be revealed as useless geegaws, to be marveled at over drinks for fifteen minutes with your friends and then cast into the silicon attic.

But apart from the incredible irony of this company suddenly being concerned with “safety” this is incredibly wrong-headed on several fronts. First, as any number of SatNav crashes have shown, taking drivers eyes and minds off the road, reducing their situational awareness, is not a good idea. Full stop. Rather than scanning some tiny screen to look for time-and-weather coded crash data, one should actually be looking at the actual conditions of the road one is on.

Then, there’s the problem of regression to the mean. A place may be an “accident black spot” for a time, then have no crashes for the next number of years. What are we to do with that information? And, given that the vast majority crashes have driver behavior at their root, not slippery bridge surfaces and the like, presenting crash data as somehow a function of road conditions is disingenuous. And, as always, does highlighting places of greater crash frequency leave one less vigilant at other locations?

The best way the iPhone could contribute to traffic safety in the car — apart from the long-awaited breathalyzer app — is it for it to be turned off.

Faithful readers of Traffic will know of my fascination with the traffic organization of ant colonies. I’ve just been reading a new paper, “Priority rules govern the organization of traffic on foraging trails under crowding conditions in the leaf-cutting ant Atta colombica,” published in a recent issue of The Journal of Experimental Biology, by Audrey Dussutour and colleagues from France’s Université Paul Sabatier.

Dussutour, working with a colony at the University of Illinois, manipulated a bridge on an ant trail so that it was too narrow for two opposing streams of ants to pass abreast. A clear pattern emerged: Ants heading out to the food source always gave way to returning ants that were laden with food (some of which were followed by ants without food). A set of “clusters” emerged, which had its own interesting pattern in same-direction traffic: Even though the ants returning without food were in theory held up by the slower, leaf-carrying ants, those ants still refused to “jostle” past. The results of this strategy were worth noting:

As unladen ants move on average faster than laden ants, these ants were thus forced to decrease their speed. By contrast, this decrease was counterbalanced by the fact that, by staying in a cluster instead of moving in isolation, inbound unladen ants limit the number of head-on encounters with outbound ants. Our analysis shows that the delay induced by these head-on encounters would actually be twice as high as the delay induced by the forced decrease in speed incurred by ants staying in a cluster.

A strategy that appeared to be slower for some individual ants actually benefited the colony as a whole; this is a pattern that often does not hold in human traffic — when, for example, individuals change lanes in unstable traffic, perhaps temporarily improving their own position but having what Benjamin Coifman terms a “butterfly effect” on the lane they have moved into, as well as the one they left.

The French team’s experiment reminded me of a passage from Robert Frank’s book The Economic Naturalist. Frank, based at Cornell, writes about the quaint old one-lane bridges around Ithaca, New York. He notes that a “first come, first served” social norm has emerged at the bridges, so that a stream of steady traffic from one direction wouldn’t hold up cars from the other direction for an undue amount of time. Typically, self-restraint, as in the case of the ants, can help improve overall efficiency.

But when traffic is heavy from both directions, he notes, this norm actually penalizes drivers. As he writes:

“Suppose a ten-car caravan arrived from each direction, with ten seconds separating the cars in each caravan, and with the first driver in the northbound caravan reaching the bridge a split second before his counterpart in the southbound caravan. If no one followed the first-come, first-served norm, all northbound cars would cross the bridge, after which the ten southbound cars would cross. Northbound cars would experience no wait at all, and as readers with a pencil, paper, and a little patience can easily verify, the southbound drivers would experience total combined waiting time of twelve minutes and thirty seconds… In contrast, if all followed the first-come, first-served norm, the first northbound car would cross, followed by the first southbound car, then the second northbound car, followed by the second southbound car, and so on. If you are patient enough to add up the relevant waiting times, you will see the total waiting time would be 80 minutes—37.5 minutes for northbound cars and 42.5 minutes for southbound cars—more than six times as long as when there was no norm.”

Of course, at construction sites and the like, where a flagman is present to wave clusters of vehicles through, this problem does not exist or is mitigated.

I am not sure what the implication of this is. Perhaps we humans simply prize courtesy over rote efficiency (though overall the logic of traffic seems to be that everyone pursues his or her individual efficiency, beyond any impulse towards altruistic politeness). Perhaps it is because we have not evolved to act in concert, as ant colonies have (as Dussutour, et al. note, “ants from the same colony presumably act with a unity of purpose very different to the multiplicity of individual interests pursued by pedestrians or drivers moving in a traffic stream”). Perhaps the Ithaca bridges are simply outmoded in an era of heavy traffic. And on those Ithaca bridges there’s no clear hierarchy of commuters, as in the ant example. But it’s not a stretch to say that a bridge metering system, perhaps inspired by some ant-traffic-derived algorithm, would get people home faster than the traditional way of doing things.