08-22-2016, 11:54 AM
Not to mention, adding a 2-pack train doesn't solve crowding issues as well as increasing frequency.
Imagine that service is every 10 minutes, and we've got such wonderful ridership growth that we find that for the entirety of rush hour every train is absolutely crammed, at, let's say, 110% of comfortable capacity. (for the sticklers out there, that's probably %70 of design capacity, which are usually very... "optimistic" packings)
6 trains over an hour, each at 110% capacity
Say you have an extra LRV, and want to add it in. You can either (A) tack it on to one of the existing runs, or (B) add a new run. The latter requires a new driver, the former does not. Let's consider the options:
(A) You get 5 runs of 1 LRV, and 1 run of 2 LRVs
That means 5 runs are still 110% packed, and the remaining is a glorious 55%. 1/6th of your riders are super happy, and the others are very unhappy.
(B) 7 runs of 1 LRV, every 8.5 minutes
That means 7 runs that are 94% packed. Everyone can now breathe.
You may rebut that rush hour isn't so spread out, and that you could just put the 2-pack on the busiest time, but keep in mind that the 2-pack can't be everywhere at the peak. At best, they can try to aim it at one specific bottleneck, but our LRT will have multiple major destinations on it, and so it will arrive at other destinations at the wrong time to serve peak there. At worst, the LRT will have unpredictable running time at rush hour, and the 2-pack will get delayed and miss the peak point crunch entirely.
It's just much more effective and reliable to increase frequency.
Imagine that service is every 10 minutes, and we've got such wonderful ridership growth that we find that for the entirety of rush hour every train is absolutely crammed, at, let's say, 110% of comfortable capacity. (for the sticklers out there, that's probably %70 of design capacity, which are usually very... "optimistic" packings)
6 trains over an hour, each at 110% capacity
Say you have an extra LRV, and want to add it in. You can either (A) tack it on to one of the existing runs, or (B) add a new run. The latter requires a new driver, the former does not. Let's consider the options:
(A) You get 5 runs of 1 LRV, and 1 run of 2 LRVs
That means 5 runs are still 110% packed, and the remaining is a glorious 55%. 1/6th of your riders are super happy, and the others are very unhappy.
(B) 7 runs of 1 LRV, every 8.5 minutes
That means 7 runs that are 94% packed. Everyone can now breathe.
You may rebut that rush hour isn't so spread out, and that you could just put the 2-pack on the busiest time, but keep in mind that the 2-pack can't be everywhere at the peak. At best, they can try to aim it at one specific bottleneck, but our LRT will have multiple major destinations on it, and so it will arrive at other destinations at the wrong time to serve peak there. At worst, the LRT will have unpredictable running time at rush hour, and the 2-pack will get delayed and miss the peak point crunch entirely.
It's just much more effective and reliable to increase frequency.