Anchoring, public transit, and development
Why are we putting towers at Marine Gateway, but not at King Edward?
I came across an interesting 2010 post by Jarrett Walker talking about the usefulness of “anchoring” a public transit route with destinations at each end, to make full use of capacity (e.g. downtown and UBC).
Alon Levy argues that this just results in more crowding.
Who's right?
Jarrett Walker on the benefits of anchoring
Vancouver: the almost perfect grid. Jarrett Walker, February 2010.
If a transit line is operating through an area of uniform density, about 50% of its capacity goes to waste. That’s because the vehicle will leave the end of the line empty, fill only gradually with passengers, and reach its maximum load at the midpoint of the line. After that, more people get off than get on. As you near the far end of the line, the vehicle is nearly empty again. If you plot the load of the vehicle against the position on the line, you get a bell curve: zero at the ends of the line and its maximum level right in the middle. If you scale your capacity to the maximum level, you end up with a lot of wasted capacity near the ends of the line and no way to make use of that capacity.
So transit planners are always looking to anchor their lines. Anchoring means designing a line so that it ends at a major destination, so that there will be lots of people on the vehicle all the way to the end of the line. A line with strong anchors at each end will have more uniform high ridership over the whole length of the line, and a much more efficient use of capacity overall.
Within this framework, Vancouver having its major destinations at the edges instead of the middle is a good thing, supporting very frequent service.
That’s what Vancouver provides, via UBC in the west, downtown in the north, and the various SkyTrain stations (opening to a large suburban area with density around many stations) in the east. Only in the south, along the Fraser River, does Vancouver just peter out into nothingness without a major destination at the edge. Major north-south routes end at points along Marine Drive, which defines the city’s southern edge, but by Vancouver standards there’s just not much happening there. From a transit efficiency standpoint, it would be a good place for some towers.
Alon Levy on anchoring
The Problem with Anchoring. Alon Levy, April 2013. Alon suggests that anchoring makes sense if you’re talking about longer-distance inter-city trains, where the key challenge is generating enough trips to justify the expense of building and operating the route. In this case, you want to have a large population centre at each end. But for urban-scale transit, what makes sense is short trips.
Both in theory and in practice, the anchoring argument fails to note that a bus with development at the ends will be overcrowded the entire way, because people will travel longer. If UBC were located around Central Broadway instead of at the very west end of the metro area, people would just have shorter travel time; at no point would there be more westbound a.m. crowding because at no point would there be more westbound passengers traveling at the peak.
On the relationship between public transit and development patterns: Alon suggests that what makes sense is continuous development along the transit corridor, rather than an anchor right at the end.
For example, in Manhattan the north-south subways fill as they go southward in the a.m. peak. This means that commercial buildings north of Midtown, generating passenger traffic that either is northbound (hence, reverse-peak) or gets off the train before it gets the most crowded within Midtown, add ridership without requiring running more trains. … This favors not outlying anchors, but development sprinkled uniformly along transit lines outside the central business district.
In Vancouver:
What this means for transit-friendly development is that it should not worry about anchoring, but instead try to encourage short trips on local transit. In his original post about Vancouver’s anchoring, Jarrett says of Marine Drive, at the southern edge of Vancouver proper, “From a transit efficiency standpoint, it would be a good place for some towers.” This is not good transit: from the perspective of both costs and ridership any residential development south of Broadway in which people take the bus downtown is equivalent, so might as well put it immediately south of Broadway or at King Edward, 41st, or 49th to connect with the east-west bus routes and let people live closer to work. Commercial development, too, is best placed just short of downtown, because if it’s on Marine Drive people will drive to it whereas if it’s along the blocks immediately south of Broadway many won’t.
Better would be to do what Vancouver hasn’t done, and encourage medium-intensity development all over the major corridors, of the kind that exists on Commercial, Fraser, Main, and 41st and allows their respective bus routes to serve productive short trips, generating low costs without excessive crowding. Towers on Marine Drive, to the extent that their inhabitants would even use transit instead of driving, would clog all the north-south buses. Mixed-use medium-rise development running continuously along Arbutus (which already has an abandoned rail corridor that could make a relief light rail line if the Canada Line gets too crowded) and the major east-west corridors would have the opposite effect, encouraging local trips that wouldn’t even show up at the most crowded point of the line.