Cost of a lane of parking

The Green Line Extension in Somerville and Medford is part of the (legally mandated) environmental mitigation for the Big Dig freeway-burying project. Like other parts of the Big Dig, there have been cost overruns and bloats in estimated cost, and it is now projected to cost $3 Billion for 4.3 miles of trolley rail.

Another way to spend money would be to remove parked cars from roads and use the extra space to establish dedicated lanes for buses (and perhaps bicycles, not sure how well that works in practice). But what would that cost?

Generously, I estimate 500 cars per mile of road – 10560 feet of road (both sides) divided by 20 feet per space, minus a dab for hydrants, driveways, cross streets, and 500 is a nice round number. The Metropolitan Area Planning Council estimates $20,000 or more to construct an urban underground parking space, not counting land. That gives a construction cost of $10,000,000. For land, compare with the Alewife parking garage, which uses 5 acres for 2733 cars, none parked underground or on the first floor. This suggests an acre, and hopefully the ground floor can have some more productive use than car storage. In Somerville, extrapolating from some recent home sales on Zillow, an acre of land costs $11 million. Call it $15M for the sake of conservatively round numbers.

Thus, the round-numbers replacement cost of a mile of both-sides street parking is $25million, or about $50,000 per space, plus annual maintenance (according to the MAPC) of up to $2000 per year. There are plenty of related costs and benefits – if there’s only one garage per mile, some people will have long-ish walks, but on the other hand the parking will be mostly covered and thus not require shoveling out in the winter. It’s likely that parking would be distributed into smaller hunks to simplify land acquisition for garages and to reduce the walking distance.

$50,000 for a parking space may sound like a lot of money, but compare it to the cost of an 8’ x 20’ piece of land at $15 million per acre. Do the math, and you get about $55,100 per parking space.

Doing this benefits us in several ways. Because buses can move more quickly, they provide a more valuable service to their users. Because buses can cover the same distance in a given amount of time, either service can be more frequent for the same cost, or else fewer buses are needed to provide the same service intervals. Street plowing and cleaning become easier, and emergency vehicles can flow more freely during rush hour. Crossing streets becomes slightly safer because parked cars will no longer obstruct views between pedestrians and drivers; each can more easily see the other. Removing parking also eliminates the cause of bicycle dooring (20% of the crashes recorded in Cambridge) and both improved visibility and the availability of the bus lane as a refuge from traffic are likely to improve bicycle safety.

There is an economic side-effect of making the cost of parking more salient; if the city is paying off a bond on a parking structure or has a budget item for parking structure maintenance, that will encourage a critical comparison of the cost of parking versus the cost of alternatives. Right now the default treatment of parking is as if it is “free”, as if there were not even any tradeoffs to be made. This doesn’t sound like a good thing to someone who is currently benefitting from free or subsidized street parking, but from an economic point of view it is likely to lead to a more efficient allocation of resources if we recognize their costs.

To return to the Green Line, its original $2Billion cost estimate would be adequate to remove parking from 80 miles of streets.