"Graham J" wrote in message ...

To run the whole service reliably (and it's designed for up to 18 or even
20
tph ultimately) with adequate turnround times and margins you'd need a
four platform station at Highbury, and there isn't room.

I was just wondering what the factors are that makes Highbury different
from other two platform terminals with higher service levels, e.g. Brixton
on the Victoria Line. That's a genuine question by the way, I am sure
they are many and various but I don't really know what they are. Paul has
already suggested that something as simple as the distance to the scissors
crossover would be one factor (assuming it couldn't have been placed
somewhere else). I wouldn't be surprised if something like passengers
tending to wait around on the platforms for a direct train instead of
taking the first one and then waiting further down the line would be a
factor too.

I don't know what the theoretical capacity of the 2 platforms at Highbury is
but even if it was possible to run more trains, it would not necessarily be
desirable. At the moment trains have a booked 10 minute turn around time
which in most cases means a late running arrival will be able to leave on
time. Cutting this would make the line as a whole less reliable.

In the case of the Victoria Line the main priority is frequency, it doesn't
really matter if every train is 10 minutes late leaving Brixton as long as
they are leaving every 2 minutes. On the ELL with a range of different
destinations and interworking with other NR services, punctuality is much
more important.

Peter Smyth