On another note, one thing I would like to model is “what’s the optimal size of a transit vehicle?” — in particular if, like in today’s systems you can have only one. (Not quite for trains which can change length.)
The first obvious thing is that there is an optimum. Make the vehicle too big, even big enough for the ridership at 5pm, and all those empty seats the rest of the day cost you too much.
Factors to put in the eventual full model would include:
- How much does extra seating capacity increase the weight, and thus vehicle cost and energy to move it?
- Less capacity means more energy per passenger in full vehicles
- Smaller vehicles can (and need to) run with greater frequency, which increases demand due to shorter wait times.
- Alternately to greater frequency, smaller vehicles can mean more routes and a larger service area for more demand.
- More vehicles means more drivers — until robocars
- More people means more starts and stops to pick up and drop off and longer waits at stops. (Regen braking only does so much.)
- Demand-response (ie. taxi-like) can involve not even going to places with no demand, but also some empty vehicle movement
- Direct A to B trips reduce overall mileage compared to trips involving transfers
- A smaller number of larger vehicles creates less road congestion
This is a complex model, and I haven’t built it in full. It might be a thesis project to do it well. However, my initial math is suggesting the optimal size is small, or rather a mix of mostly small sizes, and thus the debate here about transit. A simple demonstration of that is to take the average city bus in the USA which gets under 4mpg and carries 9 people on average. Here it’s clear that a Prius wins. (The 8mpg hybrid bus beats out the solo Prius driver but not the average 1.5 pax Prius.)