Hi, I'm working on a fiction project set in a rebuilding society 100 years out. It's fairly utopian so people are prioritizing restoring and improving train infrastructure and service pretty significantly. American cities have high speed rail connecting them, and because I'm building this story out of my daydreams, defunct short lines have been returned to service and even rural towns have some kind of passenger train running again.
The opening has the players traveling way out into the boonies, and part of setting up that 'traveling off the edge of the world' feel was having them leave whatever city they begin in by HSR, then take successively cruder public transit until the line just ends short of their destination and they have to figure the rest out on their own.
The second-to-last step in that chain is an electric self-propelled railcar traveling along a restored short line. I think the current doodlebug is a somewhat-recent thing, put together maybe within the last ten years, and probably planned to be temporary when they built it.
So my question now is: how would they build this thing? Would it be easier to convert an existing self-propelled railcar like the Budd RDC? Would it make more sense to start with a regular coach and retrofit in the batteries, motors, control station, pantographs etc?
Or would it make more sense to start from scratch? Maybe use part of an electric bus or similar?
Reuse and salvage play a pretty big role in the story, so I'll probably embellish any option with details about where the parts came from originally.
Thank you for any advice!
Does the math change at all if they're only trying to power a single electric bus converted to rail use? I'd planned on some kind of single vehicle, but I'm not sure what factors lead to such a significant draw.
Thanks!
The two major factors for vehicle energy consumption -- rail or otherwise -- are rolling resistance and air resistance. For rolling resistance, this primarily means the weight of the vehicle, because the rolling resistance is proportional to the force on the wheel bearings. And that goes up with weight.
So if you had a 40,000 lbs bus versus a (very light) 40,000 LRT car, then the rolling resistance will be similar. That said, the next biggest factor is rubber tires vs steel wheels. But since this is a converted bus for use on rails, that becomes very similar. The third factor is the number of wheels that the weight is spread over. A bus might only need four wheels touching the rails. But an LRT car might have two bogies, so maybe 8 wheels. So there'd be more resistance just because of the number of wheels, even if the LRT car weighed the same as the bus.
For air resistance, it's mostly a matter of frontal cross section and then "skin effect" along the surfaces that the air blows past. Buses and trains are mostly about the same cross section, assuming a single level bus and a single level railcar. For the skin effect, a longer railcar has more "skin" on its sides than a bus.
So overall, yes, a bus on steel wheels will likely need a lot less power than an LRT car, due to being shorter and lighter. But we need not stop with my mere speculation: San Francisco and other places still have trolley buses, which are rubber tire buses powered by overhead line. So you can probably look up the power requirement for these buses and get an idea of the power system required.
And because a converted bus sits on steel wheels and would run on gentler slopes than hilly San Francisco, it would be reasonable that a lot less power than a trolley bus would be fine in your story.
Alternatively, the trains can just run slower, since that reduces the power draw as well. But that could limit your plot, since it means rural trains might be substantially limited in speed, only due to insufficient power. Which could tilt the story into one of rebuilding the electric system, which I suspect isn't what you had in mind.