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TR: Presumably, Global Positioning System technology could be a key enabler of the entire traffic system?

KK: GPS on trucks for tolled travel is moving forward in Germany, and Oregon’s Department of Transportation is experimenting with GPS-based mileage pricing, offering gas-tax breaks according to travel distances, as recorded by position data. They aim to soon introduce a variable-pricing form of this, where peak-period driving will cost 10 cents per mile within the Portland area, again, recorded by GPS position data. I’d like to play a role in that work, by estimating the benefits (and costs) experienced by everyone in the region. Many states hope that vehicle manufacturers will pursue inclusion of GPS in all vehicles, to tame that technology’s presently high fixed costs while permitting relatively seamless tolling.

TR: You propose to evaluate the impacts of what you call “credit-based congestion pricing.” What’s that?

KK: Credit-based congestion pricing is a policy wherein tolls rise with traffic demand, thus keeping traffic moving, and distribution of travel budgets ensures a reasonable level of access for everyone. For example, the first 100 miles a vehicle travels during peak periods each month would be “free.” But after that, the driver is on his or her own, paying tolls out of pocket, via a transponder account. And the tolls would be higher during times of congestion. This incentive structure optimizes demand by allowing tolls to vary with congestion, on each link in the system across all times of day.

TR: Is there any evidence that this could work better than previous technology efforts?

KK: Our models of the Dallas and Austin systems indicate that such policies can eliminate recurrent forms of congestion while enhancing the lives of most residents. People are very interested in this form of pricing policy, as it makes good sense and resonates with the public, thanks, in part, to its equity implications – no one is priced off the network. San Jose, California’s transportation authority incorporated my ideas into a federal highway pilot program proposal, and I hope that work will be going forward.

TR: Meanwhile, is anything significantly increasing capacity on highways?

KK: Yes. We’re seeing more aggressive driving patterns, and much higher speeds. This increases capacity “naturally” from 2,000 vehicles per hour per lane to more than 2,400. Of course, at higher speeds, injury severity and survivability of crashes becomes a serious issue. Vehicle improvements are occurring, certainly; but, ultimately, there is only so much auto manufacturers can do to save us from the speed-squared law of kinetic energy.

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