America has always sprawled, and our rail systems – the historical enablers of sprawl, at least for the first eighty years or so – were adapted to traverse vast lengths of roadbed with alacrity and dispatch. Then we tore out every track we could, and our domestic railcar manufacturers either converted to bus production or folded outright.
Later, we started building rail again. We imported vehicles from Europe and Japan. And with little institutional memory, we adopted their specs as our own. Today, American rail vehicles underperform their historical predecessors. That ought to change. To wit, a couple areas which could use improvement:
For frequent stopping services, vehicle acceleration has a larger impact on schedule times than overall top speed.
PCC cars had a historical maximum acceleration of 4.75 mphps, or about .21 g. You can experience this yourself by riding any number of heritage trolley systems. Stats on older streetcars are hard to come by, but they were likely similarly peppy. More than one operator replaced the as-delivered 25hp motors on their single-truck Birney cars with 50hp units, giving them a power-to-weight ratio 30% beyond the PCC.
Even as the US operators began to abandon their systems, the Czechs continued the design, with the PCC-based Tatra T3 achieving a respectable 4.0 mphps. The T3/T4 and its derivatives continue in service today across the Eastern Bloc.
Meanwhile, the Boeing-Vertol LRV applied PCC levels of power to a vehicle that was 50% heavier, resulting in a service accel of 3.0-3.3 mphps, depending on which source you read. And the early 80’s adaptation of Frankfurt U-Bahn stock by San Diego, Calgary and Edmonton normalized its paltry 2.4 mphps acceleration in the minds of new riders.
Eventually, successive Siemens LRV designs reached the 3.0mphps benchmark. The Houston-spec S70 has a power-to-weight ratio approximately 10% higher than the PCC, but it is not designed to transfer that power to the track as the PCCs did.
Most manufacturers can design to spec if the spec is insisted upon. As an example, the Japanese have perhaps the slowest-accelerating trains of any first world nation. The original Kintetsu 6800 series, with a 2.5 mphps service acceleration, was marketed as the “rabbit car.” The revival rabbit car is even slower. Yet Kinki-Sharyo (Kintetsu’s rolling stock arm) has produced 3.0 mphps, 65mph LRVs for both Dallas and Seattle.
Instead, 3.0 mphps accel appears to be an evolved institutional preference among US transit operators. The Czech-spec Skoda 03T and its derivatives have a horsepower-to-weight ratio that bests the PCC by 50%. Yet the produced-under-license United Streetcar variant is cited at 4.4 feet per second squared – or exactly 3.0 mphps.
One of the major strikes against “modern streetcar” systems is that they underperform relative to buses operating the same routes. But it appears that this limitation is largely bureaucratic. If one US streetcar or LRT operator specs a vehicle with 5.0 mphps service acceleration, others will be sure to follow.
The top speed of the Electroliners is steeped in mythology and lore. 80-90mph seems reasonable, although some have claimed 100+. Likewise, Brill Bullets on the P&W operated at 80mph for a large part of the 20th century. And the Boeing-Vertol LRV was designed for a nominal 70mph top speed, although it only ever saw service on the notoriously serpentine alignments of Muni and the MBTA.
The commuter-oriented heavy rail systems of the 60s and 70s were designed to similarly high speeds. BART was designed to 80mph, while PATCO and WMATA were designed to 75 (since reduced to 65 and 60, respectively). Atlanta’s MARTA was designed for 70; Miami and Baltimore were the slowest, at 60.
Once again, the adoption of the Frankfurt U-Bahn as a de facto LRV standard slowed us down. The original U2 topped out at 50 mph, with subsequent derivations achieving only 55 mph. This must have seemed like a sane and reasonable speed to 1980s transit planners, although Sammy Hagar would disagree.
Dallas’s suburb-oriented LRT network required something faster, so DART spec’d a 65mph LRV. Texan rivalries being what they are, Houston also spec’d a 65mph LRV, even though there’s nowhere on the current system where it can come close to that. Seattle is also largely designed for 65, since that system is imagined to one day link the disparate satellite cities of Tacoma and Everett.
Is 80mph LRT possible? There are engineering tradeoffs to be made. Wheel profile is perhaps the most significant. Higher speeds require a flatter wheel surface, to reduce hunting. But flatter wheels don’t perform as well in tight cornering. All US LRV systems have hewed to a 25m (82′) minimum radius, another spec we adopted from the Germans. An LRV which could comfortably and reliably operate at 80mph would be unlikely to reliably negotiate these corners.
But most LRV networks don’t have minimum-radius curves on their mainline. Dallas appears to stick to 150′ and above, although some yard tracks are as tight as 90′. Houston’s yard trackage includes 82′ corners, but otherwise the only limiting factors on the Main Street line are some #6 turnouts.
Not everyone needs an 80mph LRV. Houston doesn’t, at least with the currently-proposed system. Portland probably doesn’t, given the frequent stop spacing on even outer-suburban lines. But DART, with its extensions to places like Rowlett and Buckner, could stand to benefit. And Seattle’s forthcoming lines have a stop spacing more akin to BART than the average LRT network.
An 80mph LRV, then, like a 5 mphps streetcar, is just a matter of the right agency making the right request. Who will step forward?
Updated 1/28/2015: A previous version of this post mis-stated the acceleration of the Tatra T3.