Light- and heavy-rail urban transit; why so little interoperability?

(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.

Some heavy rail systems use the same rail network as inter-city rail, and have to conform to the same standards. SEPTA in Philadelphia, for instance, has trains that share the same rails as Amtrak.

You can run a light train on a track made for heavy trains, but you can’t run a heavy train on a track only built for light rail. (The heavy train would squash the road surface, and pipes and conduits underneath, break the bridge, vibrate the buildings, liquify the soil… etc)

So light rail in heavy rail facilities ? Platform heights and offsets are an issue.

Height ? well the street car has people stepping into it from street level. The heavy rail has platforms well over a meter high.

Offset - well even if the gauge was the same, and you thought you might add stairs or ramps into the light rail to get up to the higher heavy rail platform, the heavy rail carriage is wider.

Why was light rail added anyway ? because the heavy rail network was congested.
There’s already heavy rail trains queuing up and becoming late at peak times, now you want to add light rail into it too ? Hold up a 12 car train for effectively 1/4 of a car to come through ?

It’s not unusual for local commuter systems to share track with Amtrak, and, outside the NEC, freight operators as well, but usually the commuter rail operator is a different agency from the one that operates the urban transit network. Metrolink in the L.A. area, the Coaster in San Diego, and CalTrain in the Bay Area all share some stretches with Amtrak, and/or freights.

It’s much the same in the Northwest. The heavy rail Sounder system in and out of Seattle only uses Amtrak routes (it only operates at early rush hour), while the separate Seattle and Tacoma light rails have their own tracks.

The short answer is that light rail is cheaper to build than heavy rail, so you build light rail by default, unless your circumstances (as you evaluate them) specifically require heavy rail.

So, LA County’s one non-commuter heavy rail, the Red Line, goes through a high density city core, where, in theory, it can carry the highest number of riders making the highest number of trips. Its route has also been shaped by political and geological considerations, so it falls short of the planners’ ideal, but it is mostly what they intended.

Since light and heavy rail function differently in terms of equipment, power supply, and carrying capacity, you have to choose one or the other. If you want full interoperability you have to make everything light rail, or everything heavy rail. Transit systems can upgrade (at a high cost) existing light rail lines to heavy rail, when circumstances require/allow it.

In the LA Metro system, interoperability doesn’t provide huge benefits. As it stands now, most of the rail system is interoperable, since it’s all light rail except the Red Line. Train cars are occasionally shifted between the light rail divisions (a division is the train yard and base of operations for each rail line) but most of the time, this isn’t necessary.

There might be some operational benefit to being able to throw a light rail car or two onto the Red Line in a pinch, but it’s not really a major issue.

Here’s a paper which advocates increased interoperability between heavy rail and light rail. Doing it basically requires upgrading light rail to heavy rail, and paying the attendant increased costs.

In the LACMTA (LA Metro) all rail operators are trained on all rail lines. When they complete their training, they can choose which line they work based on seniority. Though most operators stick with one line most of the time, they can and do transfer. So cross training isn’t an issue. They’re all able to work on any line they’re assigned to.

You’re assuming regional transit systems are designed as a coherent whole. Most of them seem to have developed organically as a collection of independent fiefdoms over the decades.

It’s not always possible for a region to use the same rolling stock throughout. For example, the Muni metro in San Francisco uses standard gage, but the cars are articulated and on the short side so they can wind through old tunnels and streets. BART, on the other hand, runs on Indian Broad gage on a separated right of way. The original idea was that the broad gage would make the long-distance ride smoother and more stable.

I suspect the real reason was to be selfish and not allow other traffic to use their infrastructure.

I was thinking more the other way…

This is clearly so, but I’m missing the point about why one couldn’t design cars on both types of systems to have similar floor heights. Although, obviously, most transit operators buy their rolling stock ready made so they presumably are limited to what’s available.

Not always. Here, where stations are needed in street-running stretches, the platform is built up about a meter above street level, or the track may be equivalently trenched. It’s not the best picture for the purpose, but here’s a shot of the Blue Line/Expo Line terminus in downtown L.A.; it looks like the track is at least a couple of feet below platform level


Here’s an example of a heavy rail platform similar to what exists downstairs at the same station.


It’s difficult to be sure, but it does look as if the levels in both are very close.

I didn’t think of this, so I suppose I should rather have asked why LRT and HRT systems, including the rolling stock, aren’t designed to be more compatible. I think the only way you could do that would be to design the whole system to LRT specifications; you could have high speed transit in the tunnels and rights-of-way, and slower speeds on the street as necessary.

I think this depends. In many cases, the LRT option prevailed along a given route because the ROW was already there for the most part, and elsewhere grade separation could be used. The cost of such a rail line is only a fraction of what an HRT subway would cost, and the cost of the latter may not be justifiable given the expected passenger traffic.

I don’t think LRT is usually added to augment an HRT route; they usually serve different neighborhoods/areas to begin with.

Around here the guage is the same for both kinds of trains, but the HRT cars are definitely wider.

Actually, BART’s unusual (for the US) gauge was to allow it to resist crosswinds when crossing the Golden Gate Bridge. It wasn’t until later that Marin decided not to join BARTD.

There’s not a clear bright line between light rail and heavy rail: Two Chicago “heavy rail” cars (seating 94) weigh less than one original Dallas “light rail” vehicle (seating 76). The operational characteristics of London and New York subways are inherited from mainline (“steam”) railroading, while pre-metros like Cologne and Brussels, and even the rapid transit operations in Chicago, Boston, and Cleveland can be thought of as scaled-up streetcars.

LA is strange in the different origin stories of the five lines all built just within the last 30 years. Part of it was due to changes in which agency conceived of the line, changes in what Cong. Henry Waxman would agree to allow under Wilshire, and changes in funding preferences at the federal level. And while you can always put a light-rail line in a grade-separated location to speed it up, you have to build a heavy-rail line that way to begin with.

There will be some confusion at first, but it won’t be a major problem. The transit riding public already has to distinguish between the Blue and Expo lines at 7th Metro and other concurrent stations, and between the Red and Purple from Union Station to Vermont.

The risk of confusion is also an issue on many streets serviced by different bus lines. Occasionally someone gets on a 240 bus leaving Universal City when they meant to take at 150, but regular riders figure it out quickly.

The overall value of the Regional Connector to individual riders will depend a lot on how it’s scheduled. Some trips will go end to end, Long Beach to Montclair, some will be shortlines that stop at Union Station and turn around. Other variations are possible, depending on perceived rider demand, efficiencies of equipment, manpower, track and car maintenance.

The RC will definitely take some of the load off of the Red Line in the downtown area, and provide better access overall.

I wonder how they would have managed that; the GGB barely seems wide enough for just the motor traffic, as it is.

Knowing San Francisco they’d just probably just reduce car traffic to 1 lane each direction.

As I recall, they were researching adding a lower deck with BART tracks on it. Somebody said “That won’t be too expensive, will it?” and things went downhill from there.

FWIW, this is pretty much how the BART system works, although they only get away with it because San Francisco no longer has a through rail system–the only rail line goes up the peninsula, and stops in SF; they haven’t had train traffic across the bridges in decades. Also, they’re not so much “adding lines” as “extending them”, so it’s now possible to hop on BART and commute a couple hours, one way. Yay. I’m hoping for the day they add more connecting lines, in the east, or across the South Bay through Silicon Valley, or north through Marin (or, heck, add a second, crossing line through San Francisco). Yeah, that’s gonna happen.

But in those scenarios it’s a question of different trains that start or stop at the same platform in the same station. I was thinking more of the possibility that someone might go down into one of the RC stations expecting to get the Red Line there, or vice versa. It would be somewhat like a Muni-only subway station in SF, except there, everyone knows they’re completely separate from the BART system.

I have noticed at 7th Street how in some cases when they turn the train around it will change from the Blue Line to the Expo Line.

What I’ve always wanted them to do, though I don’t think they will, is as far as possible alternate between short-line and through trains from one terminus to the other. So for example Culver City to Pasadena could be designated the “Expo-P” train, or something like that, while CC to the East Side would be “Expo-ES” or something like that. Passengers could either board the train sooner and have more transfers, or wait a few more minutes at the outset to get fewer transfers or a through train to their final destination. I’m not sure if that would be logistically possible, however.

I never thought of this before, but does your Doper name allude to some kind of occupation involving subways or tunnels?

Here in Minneapolis, where we built our first LRT within a couple hundred feet of a rarely-used heavy railroad line, we were told that the reason was ‘Federal Regulations’.

Heavy rail lines aren’t allowed to also carry LRT traffic.

You could probably get a specific exemption from the FRA, if you are willing to wait a few years for it. But you would probably have to meet all the Federal requirements for passenger traffic to do so.

I’ll chime in as someone that actually got to operate LRT vehicles briefly. In the Bay Area, our Light Rail is electric, using overhead lines that the trains access via pantographs. ‘Heavy’ Rail in the form of CalTrain is diesel-electric. The Heavy Rail trains require a higher clearance than the Light Rail Vehicles, while the light rail vehicles require wires (obviously) for power.

Our Light Rail system is governed by the Public Utilities Commision, while Heavy Rail like Caltrain is the federal railroad one (name escapes me). The Block Signaling system for Heavy Rail and Light Rail is different- our Light Rail system operates like this:

On Automatic Block Sections:
Green: Next 2 blocks clear
Yellow: Next 1 block clear, block after that may be red
Red: Next block is not clear
Green and Lunar (white): Next 2 blocks on diverging track are clear
Yellow and Lunar: Next 1 block on diverging track clear, following block may be red
Green and Yellow: Procced on next block, prepare to diverge on the following block
Lunar: Proceed at 15mph
Flashing Lunar: Proceed on diverging track at 15mph

I’m pretty sure Heavy Rail has a different system. In addition, grade-level track (street) has its own signals, and it turns out different LRT organizations have their own different signal systems. :smack:

It would be like if every city in the US had different car traffic signals; maybe green/yellow/red is what it means in San Francisco, but in Chicago they use Grey, blinking purple and skull-and-crossbones :stuck_out_tongue:

Cool and informative post by Incubus! You were a Muni operator?

Light rails are often elevated, usually when the ground is too soft or loose to allow tunnelling.

Yes and no, in Cleveland’s case. Cleveland has two different sorts of trains, operating on three-and-a-half lines. I think both would technically be considered heavy rail, but the Blue and Green lines occupy the same niche that light rail usually does: For most of their length they run down the medians of city streets, with grade-level crossings, go mostly at slower speeds, and have their entrances at ground level. This is what I assume you mean by “scaled-up streetcars”. The Red Line trains, though, run mostly parallel to regular rail lines, either down in cuts or up on embankments, have stations that are further apart, run mostly at higher speeds, have no level road crossings, and have entrances about a meter above the rails requiring raised platforms. I assume that both are considered heavy rail, because all three lines match up for three stations and the tracks in between, and use the same tracks and catenary wires.

No, the reason I included Cleveland’s Red Line was the overhead catenary rather than third rail, and the small lightweight cars (especially the original Blue Birds) capable of single-car operation.

The reason transit can’t share tracks with freight trains in the US is the enormous difference in weight and buff strength between a main line locomotive or loaded coal hopper and an aluminum-skinned transit car full of humans. A collision would be very ugly. (Though some of us feel the FRA buff-strength requirements have gone too far, and create unnecessary roadblocks for new commuter or intercity service.)

Incubus, CalTrain is suburban rail or regional rail, not *heavy rail. * BART is considered heavy rail or regional rail, thus showing how the designations overlap and depend on the nature of the network as well as the equipment used. Signal aspects frequently differ even from one railroad to another, which is why trains can’t easily use the tracks of another company and Amtrak engineers have to qualify for each railroad they run over.

the diego, any train line can be elevated—though the rubber-tired trains used in Mexico City, Montreal, and Paris have trouble running outside in the snow and ice.