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Rewarding commuters who switch travel modes or times may be more effective than charging those who drive at rush hour, a new study suggests.

For as great a problem as rush-hour traffic is in most major cities around the world, viable solutions are pretty hard to come by. Building more roads only encourages more driving, and some experts believe the only hope to the problem is congestion pricing. But to date only a small handful of cities have implemented pricing plans — Singapore, London, and Stockholm are the leading examples — and while a good deal of research points to their success, other work suggests legitimate limitations.

Congestion pricing is an economics-based approach to the traffic problem that focuses on punishing certain behaviors: in this case, driving during peak hours. But a good deal of psychological evidence suggests that rewards are often more effective than punishments at changing behavior. Studies have found that when drivers are lured onto mass transit with a pre-paid pass, for instance, they enjoy the transportation mode more than they thought they would.

A group of researchers led by Taede Tillema of the University of Groningen, in the Netherlands, recently designed a study to compare the effects of congestion pricing to a Dutch rewards program called "Spitsmijden," or "peak avoidance." In an upcoming issue of the journal Transport Policy, Tillema and colleagues report that a reward system like "Spitsmijden" may indeed be more effective than punishments.

The researchers manufactured their comparison from two previous studies of driving behavior in the Netherlands. The first was a congestion pricing survey of 562 Dutch drivers conducted by Tillema back in 2004. The respondents indicated whether or not the proposed pricing scheme would change their decision to drive during peak hours for work, social, or other situations. (The scheme closely resembled one considered by the government at the time; in 2007 Dutch officials approved a pricing plan, but it was scuttled by new leadership in 2010.) 

The rewards (or Spitsmijden) study was a true field experiment launched in October of 2006, and whose results were only recently published. This time the researchers recruited nearly 350 people who commuted regularly to The Hague on the A12 roadway from Zoetermeer, a commuter city. The commuters were offered a daily reward (between 3 and 7 euros) if they didn't drive the A12 between 7:30 and 9:30 a.m. and instead either drove at another time or commuted by another mode.

A number of caveats must be acknowledged with this type of comparison. For starters, the two studies being considered were conducted with diverging methods: one being a largely passive survey, and another an active field study. In addition, those drivers who participated in the Spitsmijden rewards program might be more likely than most of the population to find it acceptable, since they volunteered for the study.

With all that said, Tillema and colleagues found that about 37 percent of car trips were diverted from rush hour in the rewards scheme, compared to only about 15 percent estimated to change times in the pricing plan. That difference was pretty consistent across three levels of rewards and punishments. In both cases, introduction of the scheme itself produced the greatest change in behavior, with diminishing returns as the cost or reward increased:

The researchers conclude that, "in line with the principles of behavioural psychology," rewards may be more effective than punishments at changing driver behavior, but they acknowledge that more research is needed to draw a firm conclusion. As intriguing as the findings are, they come with a number of questions. The biggest, of course, is who would pay for a reward system on a wide scale?

Perhaps a more important consideration is whether or not a rewards system would do much for urban sustainability. In both the reward and punishment studies, the researchers found that the most popular alternative to driving at peak hours was driving at off-peak hours (as opposed to changing commute modes entirely). That finding was even more true of the reward participants (70 percent) than the pricing participants (50 percent). Unless cities can secure a more balanced distribution of commuters by modes at all times, they run the risk of simply expanding rush hour, rather than alleviating it.

Photo credit: Tom Plesnik/Shutterstock

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