What's it worth to turn off the escalators?

Today I passed through City Thameslink tube station at around 11am. There was nobody else there, but the escalators were all running. It made me think, shouldn't these all be on a stop-start system so they only run when people are there to go up and down them?

Here's the math. If you could stop all escalators on the tube from running 25% of the time, you would offset the CO2 produced by about 750 houses.

For comparison, if you wanted to provide renewable electricity for 750 houses, you'd need something like the micro hydro station at Garbhaig (see below) which cost about £1 million quid to build. So my thought would just be this, next time we have a million quid burning a hole in our pockets, let's put stop-start on the escalators instead of building another power station in the beautiful Scottish highlands.

Photo is from Roddy Smith and geograph. Here's the math if anyone wants to follow it through:

• A typical large underground escalator will have a 7500 W motor.
• There are 422 escalators in London tube stations.
• So to run all the escalators on the tube for 1 hour you need 3165 KWh of energy. 
• 1 KWh of energy creates about 500g of CO2 at average rates for the grid
• That's ~1.5 tonnes for all 422 escalators running for 1 hour
• You could perhaps save 6 hours running time per escalor per day
• That's ~10 tonnes CO2 saved per day or 3650 tonnes per annum
• The average UK house emits about 5 tonnes per annum
• So 6 hours saving per day for 422 escalators = 730 houses