LRT vs. BRT

To built more Rapid Transit, it should be BRT rather than LRT. Bus Rapid Transit is simply cheaper per mile, which means more of it for the same price.

LRT's advantages are as much political as technical.

First: LRT's primary advantage is that it can use rail corridors to achieve rapid transit status. Cars can't use railway right of way, so there is no competition with cars. This advantage is not limited to LRT. As both the BRT tunnels in Pittsburgh and the Orange line in LA have shown, BRT can use railway right of way quite well. Buses, driven by professionally trained drivers, can pass each easily in 22' (11' per bus). I recall the buses in Eugene, Oregon, coming scarily close. (Railway right of way is only ~22' wide at different points, which is too narrow for even two lanes of car traffic 10' lane + 10' lane + 8' safety area + 8' safety area). Word on the street is that international Fire Code mandates 26' of clear space as necessary for emergency operations.

Second, LRT vehicles are heavier, so they stop more slowly, which makes sharing a lane with cars much more dangerous, especially at high speeds, and consequently less likely to happen.A train in a highway median gets to keep its separated guide-way, and no crank(y) politician can change that. BRT 'Freeway Flyers' (BRT in an exclusive freeway lane) inevitably become BRT in a HOT lane, with consequent degradation in speed and reliability. Trains don't have the problem.

There may be one area where LRT has an actual advantage: Elevated track, with very right clearances. There have been experiments with 'guided' BRT, using things like optical sensors, guidewheels, or specially constructed guide-track. 'The Gap' between vehicle and platform can be an issue, and I'm not sure how well BRT does in that regard.

However, a 'train' portion (exclusive/separated) guideway is expensive. Denver, Seattle, and LA all achieved it by putting light rail in freeway medians. LA is increasing achieving it through the use of elevated lines (albeit at very high prices). Seattle has tunneled, at a cost of over a hundred million dollars a mile.

Previously, I've talked only about 'Rapid' transit in separated/exclusive guide-way. If we want to talk streetcars, it's only fair to compare them with their wheel counterpart, buses. The advantage of streetcar is (again) political. Chambers of Commerce like streetcars, due to their permanency. They are also cheaper and less politically fraught. A 'tram'-type light rail (AKA street-car) is cheap, because it runs in dedicated/mixed traffic right of way. So there is no need to take right of way from cars, or eliminate parking. But this type of right of way comes with costs. It makes the service slow and unreliable--it's like a bus on steel wheels.

Streetcars are also (politically) easier to build, because the FTA helps pay for them. Streetcars can get 50% FTA funding for capital expenses, such as vehicles, TSP, and station platforms. There is no reason a bus couldn't enjoy these same benefits.

Grades of Guideway

Right of way comes in three grades: 'Separated', 'Exclusive', 'Dedicated'.

Dedicated is the lowest grade. A lane nominally belongs to one mode, an obligation more commonly honored in the breach. Think of HOV lanes and bicycle lanes.


Exclusive can be though of as 'excluding'; exclusive use is maintained through barriers. Exclusive guideway is never continuous--there are always gaps in it, typically at intersections.

Separated is similar to exclusive, except that it is continuous. Typically, this requires grade separation, if only where the guideway intercepts other rights of way.


Heavy railways (commuter rail, freight rail) have separated guideway, for the simple reason that trains can't stop quickly. Where they must cross other roads 'time-separation' (railroad gates) are used. Where this generates unacceptable levels of delay for the cross-streets (a train can take minutes to pass) grade-separation is used. Typically, this requires an overpass for cars traveling over the road. In cases where there are too many roads, the railroad may be buried. The 'cut and cover' model of a trench with a roof were how the first subways were built. (Actual tunnels came later). In some cases (Alameda Corridor, in LA), digging an uncovered trench for the railway is simpler than many bridges.


Light railways have a mix of Separated, Exclusive, and Dedicated. Most light railways make use of some portion of old freight track, which are already time-separated. Some light rail systems provide Separated guideway by running down the center of freeways (Portland) or on elevated structures (Los Angeles, Salt Lake). Light rail on streets (a train in in tram-mode) typically has Exclusive guide way, with intermittent sections of Dedicated guide way. San Diego and Buffalo, two or the first cities to build light rail, made use of this. Light rail vehicles weigh less than heavy rail vehicles, and so can stop more rapidly. Streetcar/Tram vehicles weight even less, so they can stop faster and are even more suitable for on-street use.

The decision to use either Exclusive or Dedicated right of way is one of cost and safety. Without barrier separation, conflicts with turning cars results in accidents. Sadly, even Exclusive guide way is no guarantee against human stupidity.





Higher barriers, which prevent drivers from crossing them, may be safer. The trade-off is that first responders/emergency vehicles lose the ability to make left-turns and U-turns across the street, due to the curb. To accomodate this, curb heights vary between systems.





There is a fourth grade of right of way: Shared. This is what regular buses have. It offers no speed advantage to the transit vehicle over a regular automobile. Once the time consumed with exiting the flow of traffic, boarding and alighting passengers, and re-entering the flow of traffic is considered, transit vehicles in shared right of way travel at about half the speed of an automobile.


In contexts where right of way is scarce or political will lacking, Shared and Dedicated guide way are more common, to the detriment of transit vehicle speed, reliability and safety.  A streetcar operating in shared guide way has minimal advantage over a bus. (The minimal advantage  is that is cannot leave the flow of traffic, and so loses less time entering/leaving the traffic lane).



BRT systems are cheap to build, and largely unregulated. Consequently, they vary wildly. They make use of every kind of guide way.

Grade-Separated 




Time-Separated 
(LA Orange Line), for a time. Drivers ignored them, causing crashes. It still experiences issues with drivers running red lights. Grade-separation is in the works.

Exclusive - Fenced


Exclusive - Curb




Dedicated - Median



Dedicated - Side

Type of Right of Way: separated, exclusive, dedicated and mixed

For the purpose of argument, consider these the basic types of guide-way for urban transportation: Separated, Exclusive, Dedicated and Mixed.

Separated means grade-separation, either elevated or underground. There is also at-grade seperation, which is what freight lines (and most light rail systems) use, railroad gates are used to provide time-separation where roads and railways intersect.

Exclusive means 'transit only', a prohibition enforced with physical separation, typically in the form of either a Jersey barrier or a curb.

Dedicated also means 'transit only', but without the physical separation of a barrier. Typically, this is what is used for bus-lanes. Lacking physical barriers preventing entry and exit, enforcing it is more difficult. It gets used because it is a) cheap, and b) emergency response agencies oppose physical barriers that limit their ability to make U-turns across streets.

Mixed is 'mixed traffic', where the transit vehicle operates like a private vehicle.

There are some other, more exotic variants, but most of those aren't relevant, so I'll cover them in another post.