People Not Vehicles

It seems that the goal of the Maryland State Highway Administration “is to get the most vehicles through the area in the most predictable way possible.” You often see transportation departments using metrics of this sort to evaluate different ideas. And it sounds at first glance a bit like common sense. But as Dave Alpert points out a small change in wording can make a big difference:

Even pedestrians aside, the goal should be to get the most people through the area, not the most vehicles. It’s an important distinction, since one bus carries as many people as a whole lane of cars.

Indeed. If you take a big, heavily trafficked urban thoroughfare — say a boulevard with three lanes in each direction that features a somewhat frequent, fairly popular bus line — and change it to two lanes of traffic in each direction, you’ll reduce the number of vehicles but possibly increase the number of people. The dedicates bus lane will speed the buses up. And since the buses now move faster, the exact same number of buses and bus drivers will be able to service the route on a more frequent schedule, since they’ll reach the turnaround points quicker. This would make the bus service into a more attractive option and if more people take the new, faster bus the increased fare revenue could support a further increase in the number of buses and drivers serving the route.

That all would, in turn, somewhat reduce the number of cars driving the route as some people switch away from the now-less-desirable driving option and onto the now-more-desirable bus option. That reduction in car volume would, in turn, somewhat counteract the increased congestion associated with the decrease in the number of lanes. A new equilibrium would eventually be reached. To estimate whether the new equilibrium would move people faster or slower than the old equilibrium would be a bit complicated and depend on various factors, estimates, etc. But if you’re considering making the switch, that would be the right thing to consider — the impact on the volume of people, not the impact on the volume of vehicles.

Beyond that, a transportation agency should probably take a somewhat broader view of its mandate and also think about things like the impact on the environment and economic development. But, at a minimum, when looking at transportation qua transportation you should be looking at the transportation of individuals rather than the transportation of conveyances. The essence of traffic congestion is that certain kinds of space are at a premium, so ignoring the fact that different modes of move people involving taking up more or less space means you’re missing a big piece of the puzzle.