The Geary corridor in San Francisco is a neat model for transit ridership. The Golden Gate Park separates the Richmond District from the Sunset District, so the four east-west buses serving the Richmond – the 38 on Geary itself and the closely parallel 1 California, 31 Balboa, and 5 Fulton – are easy to analyze, without confounding factors coming from polycentric traffic. Altogether, the four routes in all their variations have 114,000 riders per weekday. The 38 and 1 both run frequently – the 1 runs every 5-6 minutes in the weekday off-peak, and the 38 runs every 5 minutes on the rapid and every 8 on the inner local.
I was curious about the connection between development and travel demand, so I went to OnTheMap to check commute volumes. I drew a greater SF CBD outline east of Van Ness and north of the freeway onramp and creek; it has 420,000 jobs (in contrast, a smaller definition of the CBD has only 220,000). Then I looked at how many people commute to that area from due west, defined as the box bounded by Van Ness, Pacific, the parks, and Fell. The answer is 28,000. Another 3,000 commute in the opposite direction.
Put another way: the urban transit system of San Francisco carries about twice as many passengers on the lines connecting the Richmond and Japantown with city center as actually make that commute: 114,000/2*(28,000 + 3,000) is 1.84. This represents an implausible 184% mode share, in a part of the city where a good number of people own and drive cars, and where some in the innermost areas could walk to work. What’s happening is that when the transit system is usable, people take it for more than just their commute trips.
The obvious contrast is with peak-only commuter rail. In trying to estimate the potential ridership of future Boston regional rail, I’ve heavily relied on commute volumes. They’re easier to estimate than overall trip volumes, and I couldn’t fully get out of the mindset of using commuter rail to serve commuters, just in a wider variety of times of day and to a wider variety of destinations.
In Boston, I drew a greater CBD that goes as far south as Ruggles and as far west as Kendall; it has a total of 370,000 jobs. Of those, about 190,000 come from areas served by commuter rail and not the subway or bus trunks, including the southernmost city neighborhoods like Mattapan and Hyde Park, the commuter rail-adjacent parts of Newton, and outer suburbs far from the urban transit system. But MBTA commuter rail ridership is only about 120,000 per weekday. This corresponds to a mode share of 32%.
I tried to calculate mode shares for the MBTA seven years ago, but that post only looked at the town level and excluded commuter rail-served city neighborhoods and the commuter rail-adjacent parts of Newton, which contribute a significant fraction of the total commute volume. Moreover, the post included suburban transit serving the same zones, such as ferries and some express buses; combined, the mode share of these as well as commuter rail ranged from 36% to 50% depending on which suburban wedge we are talking about (36% is the Lowell Line’s shed, 50% is the Providence Line’s shed). Overall, I believe 32% is consistent with that post.
Part of the difference between 32% and 184% is about the tightness of economic integration within a city versus a wider region. The VA Hospital in San Francisco is located in the Outer Richmond; people traveling there for their health care needs use the bus for this non-commuter trip. On a regional level, this never happens – people drive to suburban hospitals or maybe take a suburban bus if they are really poor.
That said, hospital trips alone cannot make such a large difference. There are errand trips that could occur on a wider scale if suburban transit were better. Cities are full of specialty stores that people may travel to over long distances.
For example, take gaming. In Vancouver I happened to live within walking distance of the area gaming store, but during game nights people would come over from Richmond; moreover, the gaming bar was in East Vancouver, and I’d go there for some social events. In Providence I’d go to Pawtucket to the regional gaming store. In the Bay Area, the store I know about is in Berkeley, right on top of the Downtown Berkeley BART station, and I imagine some people take BART there from the rest of the region.
None of this can happen if the region is set up in a way that transit is only useful for commute trips. If the trains only come every hour off-peak, they’re unlikely to get this ridership except in extreme cases. If the station placement is designed around car travel, as is the case for all American commuter lines and some suburban rapid transit (including the tails of BART), then people will just drive all the way unless there’s peak congestion. Only very good urban transit can get this non-work ridership.