Understanding Rapid Transit capacities

Part 3 – Capacities of rail systems

Last week we suggested that a single urban road lane can move 1,000 cars in one hour, and thus equivalent to 1,000 people per hour if there is only one passenger each (the driver), or 4,000 people per hour, if there are three other passengers (four in all). That is our starting and reference point. The true moving capacity of a transport system is measured in the number of people it can move in a unit of time. The metric is passengers per hour per direction (pphpd).

Now let’s look at rail. We commonly call this “trains,” because we have “train cars” linked together one after the other. We call them “cars” because that’s how the Americans call them – the British call them “couches” while the Indians “bogies.” One train can have only two couches, or it can have 10 or even more. The MRT in Manila has three, and it can carry 395 passengers per “train.” A 10-car train can carry over a thousand pax.

But that’s for standard trains – MRT or LRT or Metros. Trains have very diverse sizes and configurations. The smallest ones are the streetcars or trams that run on roadways, which started in the early years and which is now becoming popular again. Then there are inter-city trains and high-speed trains (like the Japanese “shinkansen”) which are bigger and faster. For commuting inside a city, we usually talk about light rail (LRT’s) or monorails or MRT’s (mass rail transit). MRTs are supposed to be bigger than LRTs but sometimes it gets confusing especially when people mislabel things. For example, LRT-2 in Metro Manila is actually heavy rail while MRT-3 has a much smaller capacity and is a light rail. I have no idea why this came to be.

We all know that trains, or rail transport vehicles, have big capacities and are generally the fastest among transport modes, but this does not necessarily translate to having the biggest capacities. What affects capacities is the term called headways, or the time between succeeding vehicles arrive at stations. If they arrive three times an hour, they have 20-minute headways, if four times, 15 minutes in-between. Trains arriving every five minutes means they arrive 12 times an hour, and theoretically can move 12,000 pphpd for trains with a capacity of 1,000.

In general, trams or streetcars are seen to carry less than 10,000 pphpd, and light rail much higher up to 20,000. Heavy rail can carry more, up to 30,000-40,000. Metros, in the megacities of the world can carry up to 90,000 and even more, with the new high-speed technologies always updating nowadays. Monorails have an even wider range of capacities, though limited to less than 30,000. But what this tells us is that rail can be as low as 4,000 pphpd or as high as 90,000 pphpd, that comparing them to ot her modes becomes meaningless unless you specify what kind of rail. This is where most errors arise whenever someone says rail has the highest capacities – you must specify what kind of rail to be meaningful. (To be continued)