Thought experiment: how much bus service can you get for the price of a parking garage?

Looking through some old data, I noticed that there's a common theme: the marginal operating cost per weekday of your typical frequent MBTA bus route is about $20,000. For example, the 1 bus is $18,456 while the 39 is $22,206. The 57 comes in at about $19,544. All of them are estimated to recover approximately half of that in fares, so overall marginal subsidy per day is about $8,000 to $12,000.

Mind you, the marginal operating cost only factors in the cost of running a bus per hour, plus the cost of driving it per mile. Maintenance, depreciation, administration and other facilities are not covered. But if they had the equipment lying around, then it might be fair to say that adding a weekday's worth of 57-like bus service costs approximately $10,000.

We know that excavating an underground parking garage can cost from $50,000 to $100,000 per parking space (sometimes more, sometimes less, depending on conditions). Speaking loosely, then, each underground parking space could cover the net cost of approximately 5-10 weekdays worth of key bus route service. Let's just assume for simplicity that every day has the same cost as a weekday. Then a year's worth of key bus route service could be covered for the same cost as 36 to 73 underground parking spaces.

A year's worth of bus service. (photo source)

Does this come up in real life? I think it's fair to expect several hundred parking spaces to be built along every core bus line every year. I can think of several hundred that came online along Comm Ave just last year, including some built at a deep (expensive) level. And another few hundred planned for Washington Street in Brighton. The Fenway is seeing plenty of garage construction despite the parking maximums in the neighborhood. Then a quick browse of the BRA's website shows 216 spaces (aboveground) for Kenmore Square, 236 spaces (3 floors below ground) on Harrison Ave in the South End, and 63 underground spaces on E Street in South Boston, just to pick a few examples.

I have been talking marginal costs up until now, but spaces are typically not added one-by-one. Instead, it's whole levels at a time. For example, a developer might propose 80 dwelling units and 60 parking spaces in an underground level. Some misguided neighbors might demand more parking spaces be added. But the only way to do that would be to go yet another level underground. Perhaps the developer can add another 40 parking spaces by doing that. The garage now costs about $5 to $10 million to excavate. Those costs are passed onto to the eventual tenants, and create more traffic and pollution in the area.

Alternatively, the developer could propose to pay for a year's worth of frequent bus service. The cost of adding that additional underground level could easily cover the marginal yearly cost of running a key bus route. Furthermore, doing so would help everyone in the neighborhood rather than a handful of car-owning tenants, would ease traffic and pollution instead of increase it, and would contribute to a better urban environment. And there's likely more than one such eligible development project per year.

I have heard people propose the option of replacing parking subsidies with transit subsidies. It's also a similar idea to value capture. It seems like it may be feasible after all. Some might say that it's unfair to put the burden of providing the public service on a private project (the usual objection to value capture) but I believe it is also unfair for the government to force people to subsidize parking spaces. If you're going to have parking quotas, which are ultimately harmful to the public, then it behooves you to allow them to be replaced by transit support payments, which are beneficial to the public.