Although it's a nice idea, TfL have already looked at
this and concluded that it would require far too much
subsidy to run - it would need the biggest subsidy per
passenger of any mode of transport in London. I

and it is more reliable and more comfortable than bus, nr or
tube. So it might be more expensive? It is much better,
perhaps that's why.

The problem with the river is that any pier will by its
nature only have half the catchment area of an inland
rail/Tube station.

true, but a high capacity boat service from the east end to
westminster would have cost a minute fraction of the cost of
the J L E. And journey times would not be appreciably
longer. I frequently use the boat instead of the jubilee,
even though the pier is a longer walk than the tube. This is
because the boat offers a vastly better service for a very
small premium.

A cheaper (or fully integrated) system, with 10 min
frequencies, would probably pull in more people ... and in
doing so would reduce overcrowding on other modes. Perhaps
the biggest boon would be to put the current approx. 20min
at peak frequency services from Thames Clippers on the
tube/London connections map. It's a great service and most
people simply don't know about it and hence don't consider
it when planning journeys.

--
u n d e r a c h i e v e r