Let's say for a minute the Interurban hadn't stopped running in 1941. It was bleeding money, but its parent company, NWP, was a for-profit entity. What if the Interurban had somehow survived?

For the sake of this exercise, I'm taking a few liberties. First, that the Bay Area had valued its rail transportation system from the 30s to the present, but had consolidated it all, as well as the Golden Gate Bridge, under the single umbrella of the MTC. Second, that European best practices had been implemented at least in this corner of the country. Third, that the Interurban could now survive on a 50% subsidy. And fourth, that Marin and Sonoma have their current populations, though with less sprawl.

Though I had originally intended for this to be a bit more a light post rather than something more data-driven, a Twitter conversation with Dan Lyke motivated me to put some numbers behind the costs of an Interurban.

Costs per vehicle-kilometer (vkm) vary widely based on the system. Vancouver's automated Skytrain system costs $2.18/vkm, BART costs around $3.50/vkm, and New York's subway costs $5.81/vkm. Using quite a few assumptions, I get an average annual operating cost between $43.2 million and $111.6 million. If we assume an average fare of $2.50 and a 50% farebox recovery rate, total ridership would need to be between 8.6 million per year, roughly the same number of transit trips on today's GGT system, and 22.3 million. With the Geary and North Beach extensions (Muni's 38-Geary alone carries over 13 million weekday passengers per year), it's entirely feasible for the system to meet BART's 80% farebox recovery.

Alas, reconstructing the system would be prohibitively expensive and politically impossible. Large portions of some major roads (Sir Francis Drake Boulevard, Fourth and Third Streets, Magnolia Avenue, Miller Avenue, and others) would need to be converted back to rail, wealthy homeowners would need to accept trains running behind their back yards, Sausalito would need to take a new elevated railway along the waterfront, Geary and North Beach would need to be torn up for a new subway, and over $10 billion would need to be spent. While the San Francisco part of the project might be worth it, for 8 million riders per year, most of them already served by transit, the cost and pain of the Marin Interurban simply wouldn't be worth it.

This map, along with all my other maps, is posted in the Map Room.

In 1941, the last ferry and the last train ran on the NWP Interurban commuter line, and Marin was handed over to the battle of its life against the car-centric development unleashed by the Golden Gate Bridge. Marinites, unlike most of the country, won that battle, and we maintained the transit-oriented development passed down from the age of rail. Most of us, though, don't even know what it looked like, and the best thing we've got are grainy maps and schedules from the 1930s. That's all well and good, but hides the structure and sinews of the system. The purpose of contemporary transit mapping is to combine not just where a system goes, but how and, to a lesser extent, when.

I've created two maps that do just that for the Interurban. The first is in an "old" style. Old printing techniques could only print two or three colors. Given that the Interurban shut down in 1941, I thought a map inspired by that era made sense.

The second map is the same thing, but in a "new" style. With contemporary printing techniques, we can do as many colors as we like. The advantage is that individual lines can be individually colored, snapping into focus what lines go where.

As you can see, it was quite a comprehensive system, at least for Central and Southern Marin. Northern Marin was served by intercity rail, more akin to Amtrak than BART, and was not part of the electric rail system highlighted here.