Comment by Animats
6 months ago
A 15 meter turning radius is tight, but not revolutionary. San Francisco's MUNI system's tightest turns are 45 feet, or 13.7 meters. The newer vehicles are designed for that, and the old PCC cars had to be modified to allow the trucks some extra rotation. The turning loop on Embarcadero near Market is that tight. There is much wheel screeching when a PCC car goes through that loop, because wheels have to slip to turn that tight. But it works.[1]
Battery powered trams have real potential, now that batteries with 5 to 7 minute charging and large numbers of charging cycles are a thing. That's compatible with typical end of line holding times. Steel wheel on steel rail is low friction, and you get most of the energy used to go uphill back when you go downhill. This could work out.
Overhead power is more efficient and sustainable though. No batteries to chug along, no batteries to replace or manufacture. And I wonder if the cost over time really makes up for hanging a few overhead lines.
> Steel wheel on steel rail is low friction, and you get most of the energy used to go uphill back when you go downhill.
If you were going up and down hills, would you still use steel wheel in steel rail unless you had some sort of cable to work with? I always thought the Muni did relatively level routes for that reason? The Lausanne m2 for example uses rubber (well, ideally you’d be able to just balance the train going up with the train going down, but that only works for simple inclines with limited stops). Actually, a battery powered rubber wheeled tram service on some sort of steep incline like SF’s cable car routes could get some wicked regen going down.
Even if level, they could still get some regen from making stops.
Modern speed control technology has expanded the incline range for steel-wheeled trains quite a bit. Inclines that would have historically pointed towards rubber-tired or non-traction systems are usually within the range of steel wheels with solid-state motor control. Basically the control of torque is much finer than in old resistance-box parallel/series speed controllers, so you can avoid slippage much more easily.
> would you still use steel wheel in steel rail unless you had some sort of cable to work with?
A rack rail is also an option, though tends towards the noisy and slow.
But yeah usually light rail keeps under 5%, and can’t really go above 10 on pure adhesion.
muni has "relatively level routes" because the routes that were preserved were ones with tunnels that buses couldn't fit through (or narrow ROW in the case of the J), and given sf geography those tunnels invariably go through hills. muni, and especially the J, is one of the steeper adhesion railways in the world
The J Church line on Muni is still a train in part because back when they were converting lines to buses, the hill on Church St was too steep for buses.
Wiki says it was more because of the private right away used, not necessarily its steepness:
> While many streetcar lines were converted to bus lines after World War II, the J Church avoided this due to the private right-of-way it uses to climb the steepest grades on Church Street, between 18th Street and 22nd Street.[9]
https://en.wikipedia.org/wiki/J_Church
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If the vehicle is battery operated there is no longer a need to use metal wheels. Something like ABS, nylon or rubber probably results in less wear and noise. (Perhaps at the cost of a bit more dust from braking though)
Metal wheels have significantly reduced friction, switching to something like a car tire would require much more frequent tire replacements and would have a lot more issues. Steel on steel is the way to go for fixed-route vehicles if possible.
Problem with rubber wheels in metros is absolutely atrocious air quality. I avoid them like the plague.
Also you have to replace tyres all the time, steel wheels last longer between services and are reconditioned on a lathe periodically instead of having to be continually replaced. It's one of several reasons why the longer term operating cost is way lower for trams than buses.
How many rubber wheel metros exist? I only know of a few -- Paris is one, but not all lines. Where do you live such you need to "avoid them like the plague"?
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What's the problem? Rubber dust? Rubber smell? Maybe even burning rubber smell?
> A 15 meter turning radius is tight, but not revolutionary. San Francisco's MUNI system's tightest turns are 45 feet, or 13.7 meters.
Revolutionary as the turning circle will be used at speed with passengers to traverse roundabouts in-lane. CVLR doesn't need turning loops, as the vehicles can be driven from either end.
Several North American older systems go down to 10-11 meters, although perhaps the tightest curves are getting upgraded over time:
LRT systems on which the existing minimum curve radius falls below 15 meters include:
• Boston—10 m (33 ft) and 13 m (43 ft) for the Green and Mattapan lines, respectively;
• Newark—10 m (33 ft);
• San Francisco—13 m (43 ft); and
• Toronto—11 m (36 ft).
https://onlinepubs.trb.org/Onlinepubs/tcrp/tcrp_rpt_02.pdf (1995)
Maintaining a quiet operation is listed as one of the advantages of the turning system for this system.