> On Sun, 07 Sep 2008 22:26:26 +0100 someone who may be Graham Murray
> gmurray.org.uk> wrote this:-
>

>> On the other hand, where a tram is running along a road, is there any
>> need for it to have separate signals? Would it not suffice for it to
>> have to obey the same red/amber/green traffic lights as other traffic?

>
> Yes, which is why separate signals are provided.
>
> There are many reasons why tram drivers may be given separate
> signals, for example if a tram is to start off before other traffic
> at a junction a separate signal is needed. The "amber" period for a
> tram is a few seconds longer than for motor traffic. It is also
> considered less confusing for operators of other forms of traffic.
>
> Having decided to provide separate signals for tram drivers the next
> question was what form these signals would take. The two contenders
> were tram stencils on coloured lights (just as there are bike (and
> possibly bus [1]) stencils in places) or white lights. In essence
> the white light system was chosen as there is less chance of
> confusion with signals for other forms of traffic.
>
> White light signals could be provided by standard traffic light
> units with clear lenses and the appropriate stencil. However, the
> "searchlight" unit was chosen as it is smaller than a three light
> traffic light unit (being fitted to the top of a pedestrian crossing
> pole is a lot neater than having a second traffic light unit beside
> the one for other traffic) and can provide a greater variety of
> indications.
>
> Given the limitations of operating on the roads I think the system
> would be hard to improve on.
>
>
>
> [1] I have a very vague recollection of having seen bus stencils
> somewhere in the UK. Bike stencils are provided in places though,
> unlike some other places, there is no stencil on the red lens.
>
>