"Matt Ashby" wrote in message
m...

If they are instructions as to where the bus
should stop relative to the sign,

They are.

why are they only placed at certain stops?

It usually doesn't matter exactly where the bus stops, unless there are side
roads or zigzags nearby.

Also, buses normally stop with the entrance next to the stop, so if a bus
stop is only served by front-entrance buses, or only served by rear-entrance
buses, putting the stop in the right place makes sure that the buses stop in
the right place.

Therefore the signs are only needed where buses of both types serve a stop
crammed between sideroads or other obstacles. With the imminent death of the
Routemaster, headstops and tailstops will disappear.

--
John Rowland - Spamtrapped
Transport Plans for the London Area, updated 2001
http://www.geocities.com/Athens/Acro...69/tpftla.html
A man's vehicle is a symbol of his manhood.
That's why my vehicle's the Piccadilly Line -
It's the size of a county and it comes every two and a half minutes