Weighted Distance-Based Tolling

So the other night I was sitting in the Taco Bell parking lot, and I was thinking about Dallas – specifically about how the NTTA got a waiver of the environmental speed limits in exchange for going to cashless tolling. They ran some computer models that showed the additional emissions from faster traffic would be canceled out by the reduced emissions from queues and acceleration at toll plazas, and now the PGBT is 70, while the DNT is 65 all the way to Oak Lawn. Interesting stuff can happen as you move to cashless tolling.

For medium to long distance trips, freeways and tollways are really excellent modes of transportation. Over a long enough distance, point-to-point travel times in an automobile on a freeway are second only to high speed rail and, for very long distances, air. The basic problem with freeways is that they get fouled up with a lot of short-run traffic that isn’t saving very much time.

For instance, if I jump on IH-10 east at Taylor Street and then get off at McKinney, I’ve just used up the same amount of space in the Spaghetti bowl as I would’ve if I was going from Katy to the UH. And since there’s only so much space in the Spaghetti bowl, it gets fouled up that much quicker.

Traditionally, cities with extensive suburban toll road networks have tended to favor distance-based tolling with mainline barrier plazas. This simplifies toll collection, since most lanes can be exact change only. Houston and Dallas work this way, as does the extensive tollway network around Chicago, the Garden State Parkway, and most of the Florida system. But there are other options.

The Shuto Expressways charge a flat entrance fee, similar to an old-school subway turnstile. This simplifies traffic operations somewhat because all toll plazas are on onramps, preventing a toll queue from backing onto the mainline. And of course the old long-distance eastern toll roads use ticket-based tolling, and the electronic systems reflect that. Get on the Penn Pike at, say, New Stanton, and no cash is deducted from your EZ Pass – it just records a note saying you got on there. Get off at Harrisburg East, perhaps headed toward Lancaster (why are you going to Lancaster?), the toll system calculates how much you need to pay and deducts that amount from your account.

With an all-electronic, ticket-based system, it would conceivably be possible to charge more money for less distance. For instance, suppose you get on the Westpark at Gessner. If you got off at West Houston Center, you might get charged three dollars. That’s a really short trip, and you’re using up Westpark capacity for the people who are trying to get from, say, Uptown to Grand Mission. But if you got off at Eldridge, maybe it only costs $2.25. Highway 6, two bucks even. Westpark and Barker-Cypress would be $1.80 – same as they are now – after which tolls would resume creeping upward with distance. This keeps the short trips off the high-speed, long-distance facility.

This sort of toll schedule doesn’t make sense for a system which is at free-flow for most of the day, as the Westpark is today. But for a system which is substantially congested, for several hours in both AM and PM peaks, it could serve as an effective traffic management tool. The Westpark is right-of-way constrained, and will probably never be expanded beyond the current four-lane section. As Houston continues to grow, this sort of toll system might prove to be the best option.

6 thoughts on “Weighted Distance-Based Tolling”

  1. The marginal cost of the marginal cost falls on the margin. margin

    I think you are correct.

    Where their are specific local constraints (like the spaghetti bowl) wouldn’t it be better to just add a toll reader and charge specifically for entrance to that constrained section. If we were going to do a London style congestion charge it should be for entering the bowl. What limits do you place on the bowl.

  2. “more money for less distance”

    I don’t think you should necessarily charge more money for less distance, but instead the per mile price should fall as the number of miles increases.

    i.e.

    1 mile=$1

    2mile=$1.5

    3mile= $1.75

    4mile=$2

    >4 miles=$.5 per mile.

  3. This is… a really cool idea. You could extend it to capacity-constrained transit systems as well. For example, there’s no reason whatsoever for an able-bodied person to take Boston’s Green Line from, say Park Street to Boylston or Haymarket to Government Center.

  4. Or you could charge the same, high, toll for anyone passing through a stretch of road. Short distance travelers would be dissuaded from using the freeway. Long distance travelers would pay more, but if the long distance toll is much higher than the short distance one (as is usually the case), the increase would proportionally be a small one.

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