[RobertSmalls]

P&G on a bike might make sense at a walking pace, but if you P&G at higher heart rates, you're doing it wrong.

OldMech,

There are none, and the bicycle is a huge improvement over going on foot. I'd love to figure out how to hook a horse's legs to a crankshaft, gears, and wheels. It might give the car a run for its money.

For entry and exit, I was picturing a second rail that you can access every few blocks. If traffic on the express rail was going 40mph, you'd need a really accurate, fast-actuating switch to move one rail car but not the next.