So, I knocked two Virginia legislators yesterday for working to push ahead construction of extensions to Metro spokes while ignoring the need for greater core capacity. That should not be interpreted as a blanket opposition to suburban transit construction. Rather, it’s important to try and plan transit construction taking into account: 1) a metropolitan perspective, and 2) anticipated land use. It’s also important to prioritize.

A reader emailed this along, noting that CTA was looking to make “speculative” expansions, that is, in anticipation of future growth. I don’t think there’s anything wrong with this. Given the relatively small geographic footprint of current dense, walkable areas, it has to be true that most future growth will take place in suburbs or exurbs. That doesn’t mean that new suburban growth has to look like old suburban growth. Much of it will be reengineering of old drivable areas into new walkable areas, a la Tysons Corner. Other development will be greenfield development, but even then such plans could look much more like the greenfield streetcar suburbs of yore rather than the tract-housing-by-freeway models popular among developers in recent decades. A principle factor enabling green development or redevelopment will obviously be transit-proximity.

But it’s important to recognize that not all transit investments are created equal. I think it’s important when asking these questions to use the guideline that everyone should pay according to the benefits they receive. Drivers and the world at large will benefit some and should provide funding toward transit construction. Developers, residents, and riders will benefit a great deal from new transit construction and should all be responsible for some of the costs of construction and operation. But here’s where things get interesting.

Developers (or land owners) should pay more for construction in cases where the change in land-use patterns is more significant. Where new construction will create a greenfield development opportunity that didn’t previously exist, developers should be on the hook for more money (and indeed, it would be interesting to see better research on just how much land-owning interests should be willing to pay for infrastructure extensions into undeveloped areas). We want developers to pay as much as we can get them to pay, because we don’t want to be excessively subsidizing sprawl.

It’s also the case that construction of a new extension into the deep suburbs will provide some small benefit those residing elsewhere on the network. A Brooklander who was previously unable to ride Metro to Centreville will now have that opportunity, which has some positive value to him. But people living on the Centreville line benefit a great deal from construction of that extension, which opens up to them the ability to Metro everywhere Metro goes. And crucially, residents living everywhere on the system benefit a great deal from construction in the core, which increases redundancy and reliability.

So other things equal, spoke lines should be subsidized less than hub lines. The problem is, other things aren’t equal. The elasticity of demand for transit increases as we move outward. Exurban riders react strongly to increases in the relative cost of transit than suburban riders who react strongly relative to central city riders. In a world where drivers are subsidized inappropriately, and where transit systems are perpetually short of money, there will be a tendency to price discriminate in order to revenue maximize — to charge central city riders more than the socially optimal rate, simply because that’s where the money can be gotten most easily. You see this most obviously in systems with a flat system fee, but it’s probably the case for most systems.

Anyway, this is a long-winded way of saying that central cities tend to get the short end of the stick on transit planning for lots of different reasons — underrepresentation, underappreciation of relative benefits, underpricing of scarce resources, and so on.