This post will be a lot shorter than the previous one, but it’s a necessary technical prelude to what will follow.
We hear a lot about the relative capacity of various transit modes, and the appropriateness of any mode depends both on its capacity and on the constraints of the alignment where it will operate.
I will start off with a familiar TTC chart (in the format presented at tonight’s public meeting) showing both the theoretical capacity ranges of various modes, and the projected demand on the extended SRT.
What Can LRT Reasonably Carry?
If we believe this table, streetcar/LRT can handle on the order of 13,000 riders, and bus/BRT can handle around 6,000 passengers at peak. These figures need to be carefully examined.
The design capacity of a 30m LRV (the size planned for Transit City routes) is on the order of 150-175 passengers depending on the internal layout. In order to carry 13,000 riders at a peak point, somewhere around 80 cars/hour must pass the peak point. This is impractical with single cars, and two car trains must be used. Even then, this is 40 trains/hour or a headway of 90 seconds.
Also, if that peak load has a major transfer point, there will be an extremely high volume of pedestrian activity comparable to what once existed between the Bloor-Danforth streetcars and the Yonge Subway where a dedicated transfer station was needed.
In practice, I believe that any headway below 2 minutes is impractical for on-street operation given constraints at traffic signals, and the TTC is already of the opinion that even wider minimums such as 4 minutes are preferable.
It is impossible to provide a 4-minute headway carrying 13,000 passengers an hour with LRT trains of a reasonable length on the surface. Conversely, if the line is in a tunnel or on a completely segregated right-of-way, then more frequent operation is quite reasonable, and 13,000 or more could easily be handled with two or three car trains. This leads to the option of branches and short-turn services so that high frequencies are concentrated in areas where there is no interference from road traffic.
If we consider the design criterion for surface operation with signalled intersections to be a 4 minute headway, then 15 two-car trains/hour at 175 passengers/car gives a capacity of just over 5,000. Reducing the headway to 3 minutes gets us up to 7,500.
What Can BRT Reasonably Carry?
For buses, the design capacity of a 40-foot bus is 50-55 passengers (depending on the model), and we can extrapolate this to 75-80 for a 60-foot articulated vehicle. Lower capacities would apply to highway coaches such as used on longer GO routes, but we are only talking about “city” BRT operations here.
A capacity of 6,000 per hour (the top end of the stated BRT capacity) would require over 100 40-foot buses/hour or at least 75 60-foot buses. These headways are below 60 seconds, something that is not feasible for a centre median operation such as proposed for Transit City routes.
Yes, buses operate today on close to one-minute headways, but they do so by passing each other at stops and running a mixture of local and express services. Such operations require passing lanes at stops and this would contribute substantially to the right-of-way requirements. Also, frequent service with comparatively small vehicles produces major capacity and congestion problems at terminals. This can be seen today at Finch Station.
In any event, if we assume a 2 minute headway of 60-foot buses, this gives a capacity of about 2,400 per hour. Higher capacities can be reached with lower headways, but the impact on other road traffic will be severe if any attempt is made to give the buses priority and hence reduce capacity for the rest of the road’s users.
The same constraints of traffic signal interference apply to buses as to LRVs, and if we are going to constrain light rail capacity to at best a 3-minute headway, then a similar approach must be taken for bus alternatives. Conversely, if we are going to talk about sub-minute bus frequencies, then we must be prepared to entertain more frequent LRT operations in medians.
On the Transit City routes, the lowest projected peak demand is on Waterfront West (2,200) with the remainder ranging from 2,700 (Jane and Sheppard East) up to 4,700 (Eglinton). Almost all of the Transit City routes are projected to have demands above the capability of buses running in a centre median. These are 2021 projections from the TTC in November 2007.
Much higher capacities have been claimed for BRT, but these are for lines with large dedicated rights-of-way, passing lanes and generous stations. These are much more akin to dedicated arterial roads than the kind of BRT we could implement for Transit City. Such operation is conceivable in the Finch hydro corridor, but that’s only one line of many, and it would address a very different demand pattern than the Transit City network.
LRT Is The Best Fit
As for the SRT technology, none of the Transit City lines, not even the proposed SRT extension, have projected demands anywhere near the 8,000/hour cutoff point where RT is excessively expensive relative to ridership.
Subways are right off of the map for all Transit City lines including Eglinton.
As I have argued before, the capacity needed for the proposed lines fits well with the capabilities of LRT and particularly with its ability to operate in a variety of configurations. It can operate off-street on dedicated right-of-way, including underground, where needed, but can otherwise stay in a street environment at moderate cost.
The challenge will be to operate the surface routes with as much reliability and comfort as possible.