[lbo-talk] A Case for a Higher Gasoline Tax

Alex zap_path at yahoo.com
Thu Jan 12 13:57:08 PST 2006


Gar Lipow wrote:
> Another problem with buses is the frequent stops. A bus has to
> stop every time a car does (stop signs, lights etc.) plus
> passenger stops as well. Remember basic physics is that power
> equals mass time acceleration (or deceleration) squared. Much
> of the energy used by buses is used in starting and stopping.

Minor correction. Power equals mass times acceleration times velocity (check the units). Put another way, any vehicle must supply energy equal to 1/2*mass*velocity^2 to accelerate from stop, and that energy is typically wasted (converted to heat) to brake. This isn't required. Regenerative brakes and some kind of storage mechanism could be used to recover much of the kinetic energy. In fact if the cars are powered with overhead wires, the recovered energy could be sent into the system and used by other trains or stored in flywheels or something. The trains wouldn't even need to carry batteries. I imagine a rail car would be pretty low friction, so most energy probably goes into breaking air resistance. It seems to me that given careful design, such a system could be made incredibly energy efficient. Has anyone explored the practical limits?

-Alex

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