(A couple of disclaimers: First, I actually belong to a transit oriented forum, but it’s really more about advocacy than technology, and I couldn’t really find an appropriate sub-forum for my question. Second, I have no technical expertise in this area so what I know, or think I know, is based merely on my observations as a passenger.)
A lot of metropolitan areas have both heavy rail and light rail systems using third rail and overhead catenary electric traction respectively. They may be operated by different agencies as in the case of the Bay Area, or by a single transit authority as in the case of L.A.
It strikes me odd, though, that there’s virtually no interoperability between the two types. LRT routes typically include some stretches of street running which brings down the average speed on the route overall, but where the trains have their own rights of way they can approach subway speeds. In L.A. a heavy-rail subway train typically reaches a top speed of about 65 mph given sufficient spacing of stations, while an LRT train under similar conditions–i.e. in the absence of crossings–reaches about 55.
Instead of having mostly separate HRT and LRT routes, then, why don’t transit agencies design the whole system as an LRT network that happens to have tunnels and subterranean stations in the urban core? Then you’d have one set of interchangeable rolling stock, one staff of operators who all pilot the same kind of train, and as new routes are added the same kind of rolling stock could continue to be used. Where necessary, existing tunnels could be leveraged for building out junctions, and schedules and routes could be configured to provide single-seat rides for those traveling the most heavily used itinerary at any given time of day.
Case in point, the Regional Connectorproject in L.A., the goal of which is to streamline several light rail routes, will entail an entirely new tunnel, along with two new stations. Granted, in L.A. more transit is always desirable, but in my opinion this new tunnel will be too close to the existing Red line route to add much value as far as transit in the local neighborhood is concerned.[sup]1[/sup] One can even see how people might occasionally confuse an RC station with a Red Line station, since they’ll all undoubtedly be branded in much the same way as Metro stations.
The downside of LRT is that it’s a bit slower and has less capacity, although the rolling stock itself is cheaper than it is for HRT. A tunnel that provides overhead traction is presumably more expensive to dig than a traditional subway tunnel, all things being equal, but on the other hand LRT rolling stock is typically narrower, so a tunnel wouldn’t have to be as wide. You would think the savings inherent in a narrower tunnel might offset the expense of overhead traction.
[sup]1[/sup]I’m not arguing against the RC project itself, but that’s really more about making transit more viable for people who want to go from one outlying area to another. For instance today if you want to go from Culver City or Long Beach to Pasadena by train, you have to take three trains. Once completed, the RC will reduce that to two trains or even a single train for the entire trip.