On Sun, 07 Sep 2008 22:26:26 +0100 someone who may be Graham Murray
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.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sep 7, 8:46*pm, Chris Tolley wrote:

Mizter T wrote:
A bus swerving to avoid a car would appear to be the genesis of the
accident. ... *if* (and that is a big if) the traffic signals had in
some way malfunctioned then things would become more interesting
given the interface between highway and tramway signalling.

I don't follow your reasoning. If the genesis of the accident is a bus
swerving to miss a car, then I can't see that the tram's signalling is
in any way implicated.


Sorry, I didn't make myself clear. In Croydon, as is the case
elsewhere with other tram systems, the highway traffic control signals
are linked in to the tram's signalling system so as to enable trams to
negotiate a variety of road junctions - this evidently requires a more
complex set of interlinking/interoperability (or even 'interlocking'
as it were) between the highway signals and the tram network's
signalling system. On top of that one can assume that at least some of
the highway signals in the area are co-ordinated with each other as
part of a traffic management setup (as I'm sure is the case in central
Croydon).

*If* the highway signals (indeed and the tram signals) had
malfunctioned then this could have caused or contributed towards the
car and/or bus (indeed and/or tram) being in the wrong place, hence
the relevance of this factor.

The reason I even mentioned signalling in the first place was the
'Croydon Today' article contained the suggestion, made by a witness,
that traffic lights might have been at fault - but one should note
that this is by no means verified information.

For the record, because local newspaper websites do get rejigged with
some regularity, here is a pertinent extract from the 'Croydon Today'
article:

quote
Road sweeper Martin Storm, 54, from Church Street, Croydon, who saw
the crash, said:
"The bus was coming up Park Street and swerved to avoid a car which
was coming down Wellesley Road.
"The bus driver swerved left to avoid the silver car. The bus driver
tried to avoid everything, but he couldn't avoid it.
"The car has got stuck between the tram stop and the bus and was
crushed.
The driver of the tram was really upset, but it wasn't their fault. I
was behind it all, there was blood everywhere."
He added: "The police told me the traffic lights had failed and were
all on green."
However while saying the traffic lights was one area which would be
looked at during the investigation, police today did not confirm they
had not been working.
/quote

Source:
http://www.thisiscroydontoday.co.uk/...l/article.html

Mizter T wrote:

On Sep 7, 8:46*pm, Chris Tolley wrote:

Mizter T wrote:
A bus swerving to avoid a car would appear to be the genesis of the
accident. ... *if* (and that is a big if) the traffic signals had in
some way malfunctioned then things would become more interesting
given the interface between highway and tramway signalling.

I don't follow your reasoning. If the genesis of the accident is a bus
swerving to miss a car, then I can't see that the tram's signalling is
in any way implicated.


Sorry, I didn't make myself clear. In Croydon, as is the case
elsewhere with other tram systems, the highway traffic control signals
are linked in to the tram's signalling system so as to enable trams to
negotiate a variety of road junctions - this evidently requires a more
complex set of interlinking/interoperability (or even 'interlocking'
as it were) between the highway signals and the tram network's
signalling system. On top of that one can assume that at least some of
the highway signals in the area are co-ordinated with each other as
part of a traffic management setup (as I'm sure is the case in central
Croydon).

*If* the highway signals (indeed and the tram signals) had
malfunctioned then this could have caused or contributed towards the
car and/or bus (indeed and/or tram) being in the wrong place, hence
the relevance of this factor.

Okay, that's clearer. Thanks.

--
http://gallery120232.fotopic.net/p9632771.html
(20 077 at Buxton, Jun 1985)

On Sun, 7 Sep 2008 14:28:56 -0700 (PDT) someone who may be Mizter T
wrote this:-

Sorry, I didn't make myself clear. In Croydon, as is the case
elsewhere with other tram systems, the highway traffic control signals
are linked in to the tram's signalling system so as to enable trams to
negotiate a variety of road junctions

The tramway signalling system [1] makes a request to the traffic
light controller. The request informs the traffic light controller
that a tram is approaching or waiting depending on circumstances.
How the traffic light controller responds to this request depends on
the junction and the circumstances at the time. At one extreme it
will respond immediately and change the other lights before giving a
proceed signal to the tram driver. At the other extreme it will note
the tram request and fit it in when a suitable opportunity arises.

The priority of a tram request may be increased if the tram comes to
a stand at the junction. It all depends on the junction and how that
is linked to other (road) junctions.

Many road junctions may be linked and the road bods may not give
trams absolute priority. However, trams are carrying many people in
a small amount of road space and thus can be given a high priority
than other forms of traffic.

[1] generally just detector loops. An advance detector is placed
some way in the rear of the signals. A stop detector is placed at
the stop mark. A cancel detector is placed after the lights, if the
proceed signal has not already been replaced by the white dot then
this detector will initiate this. One detector can perform more than
one function, for example a cancel detector can also function as the
advance detector for signals further along the tramway.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In message , Arthur
Figgis writes

It seems to be a slightly out-of-the-ordinary accident - the tram and
bus have ended up quite a way from each other.

According to several eye-witness reports, the bus driver was knocked
unconscious in the collision, but the bus continued running in gear
until brought to a halt when it rammed a parked car. One can only
speculate how worse the tragedy would have been on a weekday.
--
Paul Terry

In message , at 19:51:23 on Sun, 7
Sep 2008, Paul Terry remarked:
According to several eye-witness reports, the bus driver was knocked
unconscious in the collision, but the bus continued running in gear
until brought to a halt when it rammed a parked car.

So did the bus swerve around a car and hit the tram, then later hit a
car; or are there two dented cars? They "both" seem to be silver.
--
Roland Perry

Arthur Figgis wrote:
There was an accident involving a bus, a (reported to be parked) car, a
tram, and possibly a moving car, in George Street, Croydon this morning.
Unfortunately the pedestrian was killed, and the bus driver injured.

It seems to be a slightly out-of-the-ordinary accident - the tram and
bus have ended up quite a way from each other.

http://www.thisiscroydontoday.co.uk/...detail/article.

http://www.dailymail.co.uk/news/arti...e-Croydon.html


(people should avoid the Mail's pictures if they would be offended by
knowing it is tram 2534).

The bit that makes the least sense to me is the line, in both papers,
"sending the bus careering about 100m down the road". 100m is a long
way for a bus to travel apparently not under control.

Robin

R.C. Payne wrote:

The bit that makes the least sense to me is the line, in both papers,
"sending the bus careering about 100m down the road". 100m is a long
way for a bus to travel apparently not under control.

If you started an ordinary car and put it into low gear before jumping
out of it, how far do you think it would go? (NB I am not advocating
anything other than a thought experiment.)

--
http://gallery120232.fotopic.net/p9633014.html
(45 145 at Leicester, 3 Sep 1979)

R.C. Payne wrote:
Arthur Figgis wrote:
There was an accident involving a bus, a (reported to be parked) car,
a tram, and possibly a moving car, in George Street, Croydon this
morning. Unfortunately the pedestrian was killed, and the bus driver
injured.

It seems to be a slightly out-of-the-ordinary accident - the tram and
bus have ended up quite a way from each other.

http://www.thisiscroydontoday.co.uk/...detail/article.

http://www.dailymail.co.uk/news/arti...e-Croydon.html


(people should avoid the Mail's pictures if they would be offended by
knowing it is tram 2534).

The bit that makes the least sense to me is the line, in both papers,
"sending the bus careering about 100m down the road". 100m is a long
way for a bus to travel apparently not under control.

Robin

A lot of the buses near me do that every day.

--
Tony the Dragon

On 8 Sep, 11:47, "R.C. Payne" wrote:

Arthur Figgis wrote:
There was an accident involving a bus, a (reported to be parked) car, a
tram, and possibly a moving car, in George Street, Croydon this morning..
Unfortunately the pedestrian was killed, and the bus driver injured.

It seems to be a slightly out-of-the-ordinary accident - the tram and
bus have ended up quite a way from each other.

http://www.thisiscroydontoday.co.uk/...an-killed-tram.....

http://www.dailymail.co.uk/news/arti...s-horrific-bus...

(people should avoid the Mail's pictures if they would be offended by
knowing it is tram 2534).

The bit that makes the least sense to me is the line, in both papers,
"sending the bus careering about 100m down the road". *100m is a long
way for a bus to travel apparently not under control.


The Croydon Advertiser (aka This Is Croydon Today) story suggested
that the bus driver may have been knocked unconscious after colliding
with the tram, which would go towards explaining the distance the bus
travelled whilst out of control.