In a recent post on stop spacing, I quoted an eloquent defense of very closely-spaced stops based on the needs of mobility-limited persons. This view is unfortunately in tension with the need to move stops as far apart as possible to increase the speed and reliability of operations, and thus attract more passengers.

I was surprised at how many comments suggested that the answer is to provide a mixture of local-stop and limited-stop or "Rapid" services. This is absolutely the right thing to do on the extremely major streets where you can afford very high frequency (say, every 10 minutes or better) on both patterns. Most New World cities have just a handful of these streets. Examples include Mission and Geary in San Francisco, Broadway and 41st Avenue in Vancouver, Western Avenue in Chicago and Wilshire in Los Angeles. Key features of these streets are (a) very high demand supporting two frequent services and (b) relatively long trips, so that speed advantage of a rapid stopping pattern outweighs the longer walking time it may require.

But if you can't afford high frequencies, overlaying local-stop (every 200m or less) with Rapid or limited-stop service (every 800m or more) can be really unsatisfying. Should you wait 11 minutes for a local at your stop, or walk to a Rapid stop 400m away where the next bus comes in 14 minutes but might be faster? Those are the uninspiring choices presented to a customer when the frequencies are only, say, every 15 minutes but two patterns are being offered.

When you consider the major streets that support frequent locals plus frequent rapid services, Seattle's long and busy Aurora Avenue might come to mind, but in fact, King County Metro abolished that pattern a few years ago, creating instead a single stopping pattern so that they could run the highest possible frequency. That's the key. Especially for trips of under 10 km or so, waiting time easily overwhelms in-vehicle time in determining door-to-door travel time. So in those cases a reasonable "compromise" stop spacing — not as close as senior/disabled advocates want, nor as far apart as speed advocates want — is actually the fastest at getting everyone where they're going.

Another approach, which I advocate looking at, is to accept that the constituency for very closely-spaced stops may also accept poorer frequency. If you look at the part of a route that is halfway between two Rapid stops, and thus most dependent on the local stops, and you then subtract all the people there who are willing to walk 400m to the rapid stop, you end up with a fairly small number of people. So perhaps locals should be less frequent than rapids. Transit agencies sometimes try to be neutral about this, carefully calibrating local vs rapid service based solely on current ridership. But in fact, transit agencies have a strong reason to prefer rapids: faster service is cheaper service to operate, because transit vehicles complete their cycles is less time, and we pay drivers by time, not distance.

But it's definitely not adequate to say that we can resolve the conflict between close and wide stop spacing simply by running two separate lines on the same street. We can in a few places, and if public transit had a lot more money we'd do it in a few more. But transit agencies need a stop spacing policy that works for the more ordinary street, where you can afford maybe 10-15 minute frequency on just one line. That means just one stopping pattern, so we have to pick one.