Generally, the best guide to where a city should build rail lines is where the busiest buses are. However, there are exceptions. I have written two posts about this giving examples of exceptions, and am going to give a third exception; I also intend to write a separate post soon giving a fourth exception.
The first post, from four years ago, deals with cases where the bus alignment has to stay on a major street, but some major destinations are just away from the street; a subway can deviate to serve those destinations. Examples include Old Jaffa in Tel Aviv near the north-south spine of bus lines 1 and 25, and Century City near the Wilshire corridor. Here, buses are a good guide to corridor demand, but the rail line should serve microdestinations just outside the corridor.
The second post, from last year, is more properly about corridors. It describes street networks that are hostile to surface transit, by featuring narrow, meandering streets. The main example is Boston, especially the Green Line Extension, in a rail right-of-way in a city infamous for its labyrinthine streets. Another example is the Evergreen extension in Vancouver, serving Coquitlam; the bus the extension replaced, the 97-B, meandered through Coquitlam since the streets were so poorly configured, while the extension uses a short tunnel and runs parallel to a railroad.
In this post I’d like to expand on a point I made, obliquely, in the Voice of San Diego. In San Diego, there’s an under-construction light rail extension, in a rail right-of-way, into an area with not-great bus ridership. Consult the following map:
Preexisting light rail (“Trolley”) is in black, the extension (of the Blue Line) in blue, the parallel north-south arterial in purple, and two buses in green and red. The bus ridership on Ingraham is very low: the bus route running on it, 9, has 1,500 riders per weekday (source). The top bus in San Diego, the 7 (going north of downtown, then east), has 11,000. So on the surface, this suggests there isn’t much demand for north-south transit in that area of the city, called Pacific Beach.
But that’s wrong, because in an auto-oriented city like any US city except New York, the major streets are determined by car access. The relentless grids of so many North American cities – Chicago, Los Angeles, Toronto, Vancouver – are not just where the buses go, but also where the cars go. Even in Manhattan, if you have the misfortune to find yourself going east-west in a car, you will probably use one of the major two-way streets, like 14th or 42nd, which are less clogged than the one-way streets in between. Non-gridded street networks for the most part obey this rule too – the commercial streets tend to be the wider ones used by car through-traffic.
Freeways throw a wrench into this system. They offer a convenient route for cars, but are abominable for commerce. Locations 5 minutes by car from the freeway are good; locations right along the freeway are not, unlike ones right along an arterial road. The main car route from Pacific Beach to the CBD is taking an east-west arterial to the I-5, not going south on Ingraham. This means that the demand for north-south traffic actually shows as strong commerce on east-west streets, hosting bus routes 27 and 30, and not on Ingraham. The 27 has weak ridership, and the 30 has strong ridership but not right along the I-5. But in a sense it doesn’t really matter, because, like the car- and bus-hostile narrow streets of old city centers, the freeway-centric road network in that part of San Diego suppresses bus ridership relative to future rail ridership.
In the presence of rail, the strong routes are the ones orthogonal to the rail line. Here, the 27 and 30 already preexist; there is a planned Trolley stop at the intersection with the 27, and presumably the 30 will be rerouted to serve that intersection rather than to duplicate the trains along the freeway. (I tried talking to the transit agency about this, but didn’t get any useful answers.) So the decent east-west bus ridership in Pacific Beach is actually an argument in favor of a north-south rail extension.
Like every exception to a general rule, this is not a common scenario. So where else are there cases where this special case holds? The necessary elements are,
- The city must be auto-oriented enough that car access is crucial to nearly all commercial drags. In Paris, it doesn’t matter how you reach the Peripherique by car, because car ownership is so low.
- The city should not have a strong mainline rail network, which leads to a hierarchical transit network (buses feeding train stations), in which both buses and cars use the same major streets to reach train stations. This means that Sydney and Melbourne are out, as are German cities short of Berlin and Munich’s transit mode shares.
- The city must have a strong network of urban freeways, disrupting the street network to the point of siphoning traffic away from the surface streets that would otherwise be the main routes.
As it happens, all three elements are present in Tel Aviv. North-south travel within the region uses Ayalon Freeway, inconveniently east of the traditional city center; the city has been building a CBD closer to the freeway, but it’s still not quite there. This suggests that traffic is suppressed on the north-south arterials to the west – Ibn Gabirol (hosting the planned second line of the subway) and Dizengoff (possibly hosting the third) – is suppressed, and those streets require subways. This is in part why, before the Red Line began construction, I argued in favor of putting a north-south subway under Ibn Gabirol, and not under freeway-adjacent Namir Road, where the Red Line goes.
In the future, this pattern suggests that Tel Aviv should make sure to build north-south subways under Ibn Gabirol and Dizengoff, and extend them north. The significance of the northern direction is that the effect I’m describing in this post only works when car ownership is high; Israel is poor enough that car ownership is not universal, and in the poorer southern suburbs it is low enough that the buses do give a good guide to corridor demand, whereas in the northern suburbs everyone owns a car. There is likely to be suppressed transit demand in Herzliya, Ramat HaSharon, and northeastern Tel Aviv (including Ramat HaHayal, an edge city with many tech jobs). Thus ridership on a subway line going elevated over Sokolov in Ramat HaSharon and Herzliya, or on Raoul Wallenberg to Ramat HaHayal, is likely to be higher than present-day bus ridership suggests.
An American example is Washington’s suburbs. The Metro extensions are planned with little regard for bus ridership. While the Silver Line is bad for multiple reasons – high construction costs, service to too far exurbs, too much branching on an overloaded trunk – the extension to Tysons Corner is its one good aspect. There is no point in discussing bus ridership at an edge city like Tysons – conventional buses wouldn’t be following the same route that the cars follow, and freeway express buses almost universally have trivial ridership.
Finally, Vancouver. While Vancouver itself is gridded, its suburbs are much less so. In the suburbs served by the Trans-Canada Highway, especially Surrey, it’s likely that car traffic mostly follows roads feeding the highway. People drive to their jobs in Downtown, Central Broadway, Metrotown, or any of Surrey’s internal centers; there aren’t a lot of park-and-rides at SkyTrain stations, which instead emphasize transit-oriented development, and in Surrey there are actually more park-and-ride spaces at the freeways, with express bus access, than at the one SkyTrain stop with parking, Scott Road. This suggests that there is suppressed bus ridership in Surrey and Langley parallel to the Trans-Canada, along Fraser Highway. Extending SkyTrain in that direction is on a distant priority list for the region, and this theory suggests that it should be moved up, to be just behind the Broadway subway to UBC.