Driving In Traffic

Michael Giberson

The latest Review of Network Economics, which focuses on road transport issues, arrived just after the latest family Thanksgiving trip down I-95 in the Eastern United States. Traveling on I-95 prompted me to wonder how I should be driving in traffic so as to minimize the negative externalities I was imposing on everyone behind me – something I wished the vehicles in front of me were doing. The RNE didn’t answer that question, but it did have a number of interesting reports on road pricing.

In a tangentially related development, I see that Yahoo has added traffic information to its mapping service. (Found via John Battelle’s Search Blog) According to the map for Washington, D.C., I-66 East to GMU’s Arlington campus is the usual slow but steady pace for this time of day.

In less happy transportation news, Patrick Crozier’s Transport Blog has reached the end of the line.


13 thoughts on “Driving In Traffic

  1. Mike,

    The pace of vehicles between the white lines in parking lots is also “steady” (at zero).

    The morning traffic jam on I66E now begins in Gainesville or Haymarket, depending on the day. I don’t know how much of this “fun” you get to have every day, but I envy you none of it.

  2. To the extent possible, I work at home until mid-morning and drive to Arlington off-peak (or not at all!).

    My trip home usually does run during the afternoon peak and HOV restrictions for I-66 West, and so I take Lee Highway instead. Fortunately, I live in Falls Church, so the drive is not too bad in any case.

  3. Most traffic is due to the reaction time of the human being controlling the vehicle (about 1 second). When volumes increase on the highway to a critical mass a congestion effect, which has been modeled using pipe flow dynamics, tends to build up. Even though much of the traffic is not due to a physical constraint creating a backup our slow reaction times lead to cascading backup that multiplies until it reaches gridlock.

    There are a couple of solutions to limit the 1-second externality you are applying to everyone else some are more high tech than others. In some areas of Europe the police literally control traffic flow by forming something of a moving blockade going down the highway at a reduced speed. This increases the buffer zone if you will between congestion ahead and the traffic behind the police car line. Although individual speeds are reduced the flow reaches a steady constant pace and everyone is better off than if they were rushing for every inch.

    Another solution is a little more high tech. Many luxury cars now offer automatic cruise control, a feature where the cruise control will match your speed to the speed of the car in front of you. In simulations this feature is shown to eliminate normal congestion due to braking when used by only 70% of cars on the road.

    Unfortunately when you try and slow down to reduce stop and go congestion someone is going to cut you off to try and get that extra inch. As for the technological solution, even the best simulations can’t model the real world perfectly and the benefits of this technology are probably over states. Inevitably you have to ask if trying to fix the traffic problem is a worthwhile investment? I would say it is not because the rule tends to go that every time there is some investment in congestion relief, such as expanding roads, the resulting increase in traffic more than offsets the congestion savings from the investment. In short, if you lower the cost of commuting you will almost always attract more customers.

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