In article m, Martin
Underwood writes
This is an issue in the plans for Watford Junction.

If it's a level crossing and it's on the main line (as opposed to the branch
to St Albans)

or the Watford High Street branch (though very little of that is at
ground level).

that the delays for road traffic will be horrendous given that
it would probably be a full-barrier crossing linked with the signals, rather
than an AHB activated by the trains which would require less lead time
between the barriers going down and the train arriving and would probably
allow the barriers to be lifted briefly between successive trains.

An AHB is not permitted where there are more than two running lines, or
where speeds exceed 100mph. Furthermore, they are not permitted if
there's any practical risk of a traffic jam "blocking back" as far as
the crossing, or if for any other reason the road exit could easily
become obstructed.

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