On Tue, 3 Jan 2006, Brimstone wrote:

Tom Anderson wrote:
On Mon, 2 Jan 2006, Bob wrote:

Does anybody know if humps are still built into station tracks on new
tube lines.

The CTRL seems to do it:

http://www.ctrl.co.uk/route/tile1.asp?L=8

Although i don't know if that's really about playing tricks with
energy, or wanting to keep the tunnel nice and deep where possible.

When done by the CRL I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains. However
good the braking and acceleration of a vehicle on the level it will be
enhanced by going up/down hill at the appropriate moment.

Er, that *is* playing tricks with energy - the uphill slope of the hump is
a machine which converts the train's kinetic energy into gravitational
potential energy, thereby assisting the brakes, and the downhill slope is
a machine which does the inverse, delivering energy into the acceleration
process, and so assisting the motor.

It's exactly like using regenerative braking to turn a train's kinetic
energy into electrical energy during braking, which can then be
reconverted into kinetic energy during acceleration - only the hump does
it rather more reliably and efficiently!

A third equivalent would be a colossal spring lining the tunnel, which the
train would compress during braking, and whose expansion would assist
departure. Far less efficient (ISTR that you lose at least half the energy
to heat when you do that), and probably not the most reliable or safe
approach, either.

tom

--
Plus, you gotta understand I can now type far, far faster than I can
think. This is not boasting - its admitting a personal tragedy. -- D