On Transport has a nice post on the Detroit People Mover, a loop that connects a number of major employment and activity centers in downtown Detroit.
In a recent post I argued that downtown shuttles aren’t of much use unless they’re extremely frequent. The Detroit People Mover doesn’t have that problem; it runs every 3-5 minutes. It has the other common problem of downtown shuttles: it’s a big one-way loop.
(Detroit’s loop is clockwise, having reversed direction in 2008. Some one-way loops, like the one at the heart of Melbourne’s train system, also reverse direction in the middle of the day.)
In a one-way loop, the the way you go from A to B is completely different from the way you go from B to A. It’s likely to be much longer or shorter. In fact, the more direct the service from A to B, the more circuitous it’s likely to be if you want to come back.
Whenever someone proposes a one-way loop as the solution to their transit problem, especially downtown, I feel the need to take a deep breath and offer — in my most calming and supportive voice, as though speaking to someone standing on a ledge — this crucial bit of wisdom that it took me years of study to acquire:
Very few people actually want to travel in circles.
Sometimes, of course, a loop serves a rational non-transit agenda. Managers of a city’s tourism industry, for example, don’t particularly want tourists to get where they’re going. They want instead to create an experience that will show them other places that visitors might not have intended to go, and that might even be used to tour the city and come back to where you began.
But even where this isn’t the purpose, some people are just comforted by loops. Transport planners describe our travel demands in terms of “desire lines,” straight lines from where people are to where they want to be, but some people seem to have “desire loops” instead. When community leaders are asked, in a meeting, to talk about their transit needs, it’s not uncommon for one of them to say, usually with circular hand gestures, that they need some kind of loop. (The same people may use the word linear to mean narrow-minded or conceptually trapped.) Straight lines can seem so aggressive, while loops offer a sense of closure or embrace. And as a model of the fundamental nature of being, there’s a lot to be said for the loop. See, for example, the medieval notion of the wheel of fortune, or the “cycle of death and rebirth” that underlies Hinduism and Buddhism.
For whatever reason, there are a lot of one-way loops out there. In transit, one-way loops do have their legitimate uses, but they’re very specialized:
- When you’re spreading a very small quantity of service over the largest possible area, with no concern for travel time, one-way loops are the answer. Bus systems in small cities or low-density suburbs, where the goal is exclusively to provide lifeline access to the most transit-dependent persons, often use one-way loops for this purpose. (As these systems grow, undoing these loops becomes a crucial restructuring step in the maturation of the system.)
- In a very small circulator system, with very high frequencies, loops can be logical. There’s nothing wrong with a one-way loop inside an airport, for example, where there are just three or four stops and the whole cycle is done in just a few minutes. There’s no significant penalty to going the long way around the loop.
- Bus lines and some rail services need to make one way loops at the end of the line to turn the vehicle around. (Most trains and some streetcars can be operated from either end, so they can reverse direction in place without looping.) The best practice is to make these turnaround loops as small as possible to minimize the number of people affected and potentially confused by them. In the best case, a station or interchange provides the turnaround capability so that there’s no need to loop on streets at all.
Two-way loops, of course, are a totally different topic (and can often be a ground of compromise between linear and circular modes of thought). On a two-way loop, any portion of the loop can be experienced as an ordinary two-way route; some are even described as two or more linear routes that happen to be connected at the ends.
But be careful with one-way loops. If you connect all the important dots in your downtown, and you call that your ideal route, you’ll probably find that you have some kind of loop. Tourists will ride it, including locals visiting your downtown for pleasure, but it will have very little relevance to anyone else. Most of our transit desires, I’m sorry to say, are linear.