[Alon Levy’s] post on The Transport Politic about through-routing commuter rail in New York brought up a question I’ve had for several years regarding transit systems. Why isn’t through-routing more common? This applies to rail, BRT, regular bus, etc. It seems that through-routing all or most of a city’s lines via a central transit center provides all the benefits of the “hub-and-spoke” model but also eliminates the need for transfers for a significant minority of people. Is there a downside or cost that isn’t apparent at first?
- Fewer “transfers.” Some people are actually going from Connecticut to New Jersey, for example, and through-routing lets them make this trip without changing trains. More commonly, a lot of people from the north (i.e. Connecticut) are going to southern parts of New York City, while a lot of other people from New Jersey are going to northern parts of the city, and a through-routed system serves both groups, which are briefly on the train at the same time in the city. Because of the decentralised structure of Paris, lots of Parisians are riding across the city to the far side, in both directions, so the RER’s through-routed structure is absolutely essential to avoid forcing huge masses of people to change trains.
- Reduced need for terminus facilities on expensive downtown real estate, thus potential for higher frequency. Ending a line downtown means having facilities to store a bus or train for at least a few minutes, consuming expensive space. Trains typically reverse direction at an end-of-line station, so the driver needs to close her cab, walk the length of the train, and get herself set up on the other cab; she may also be entitled to some break time. A train occupies one of a limited number of rail tracks while this is happening, so this function becomes THE limiting factor on the frequency of the whole line. Downtown, there are lots of physical and cost constraints on station design, so you almost never have as many rail tracks as you’d like. Buses need space to turn around. Their drivers, too, are entitled to some break time at the end of a trip, so end-of-line stations on frequent services need space for a number of buses to pile up in a first-in-first-out queuing arrangement. All this takes a lot of space. This space is a lot cheaper at the end of a suburban line than it is in the middle of downtown.
- Fewer line ends for reduced operating and capital cost. The time it takes to turn a bus or train around, and provide the driver break, is usually not related to the length of the line. Through-routing two routes eliminates two ends-of-lines, which reduces the cost, both operating and capital, of those inefficient turnaround movements. Often, through-routing two lines actually reduces the number of buses or trainsets required by one or two.
- Fewer vehicles downtown providing the same service. Sometimes, the pre-through-routed lines overlap in downtown. Through-routing eliminates that overlap. Instead of having a bus dropping off passengers interacting with another bus picking up passengers, you have one bus dropping off passengers and picking them up at the same time. For buses especially, downtown street capacity is a very limited resource in big cities. Through-routing helps economise on it.
So why isn’t there more through-routing?
- Unbalanced markets on the two sides of downtown. There’s never an exact one-to-one match between routes approaching from one direction and those approaching from the opposite direction. For example, San Francisco’s downtown is on the bay at the northeast corner of the city, so there are no routes extending north and east that could be paired to routes flowing south and west. To the extent that such through-routes have been created (e.g. San Francisco’s Muni Metro T line) the result is a circuitous approach to downtown for one of those lines.
- Excessive line length. The probability that your train or bus is delayed is directly related to how long it’s been running since it last had an end-of-line break. (When a vehicle arrives late at the end-of-line, its break time is reduced so that it can leave on time or at least not as late.) Through-routing makes lines longer, so it can compound this problem. This is obviously more of an issue in services that are exposed to more causes of delay, such as services in mixed-traffic and services with driver-administered fare collection.
- Jurisdictional barriers. Finally, there are plenty of cases where through-routing would be in order but the two sides of downtown are different jurisdictional turf. They may be different states, as in New York, or different transit agencies. In the UK and Australia, they may be different private operating companies. Although both are government-subsidized, UK/Australia governments tend to defer to private companies about network design, so you often get designs that reflect company turf boundaries rather than efficient use of subsidies or meeting the needs of the customer. (London is an exception. Some Australian states are also working on this problem.)
- Infrastrucutre barriers. Your great-grandparents’ jurisdictional barrier is often your infrastructure barrier. New York City is the obvious example. Because each commuter rail line was designed by a separate entity, and each of these entities was thinking only about getting people into Manhattan, the terminal stations are not physically connected in the way you’d need in order for trains to flow through. This is the cause of most of the capital expense in Alon Levy’s proposal for New York above.
- They just haven’t thought of it. If your transit agency has non-through-routed lines, and you can’t figure out why, send them a link to this post and ask them!