[TCUG] Re: 'Wacky ideas'
- From: "David Overton" <dtoverton@xxxxxxxxxxxxxx>
- To: <tcug@xxxxxxxxxxxxx>
- Date: Fri, 11 Jun 2004 12:26:12 +0100
Most of these ideas were aired pretty extensively between TCUG and DfT (or
whatever they were then) in the 1980s - but that is not necessarily a reason
for not bringing them up again.
Magic green arrows
I raised this with DfT in the early 80s after moving to Manchester and
finding half the signalled intersections with early starts. An attempt to
convert them to early cut-off produced, if anything, an increase in
accidents and was abandoned. To find a way to signal them more positively,
discussions were held, but the only acceptable solution was the disappearing
green arrow which we have today. Note that the significance of the
indicative RT arrow (= protected movement) as traditionally used in early
cut off, was not then covered in TSRGD nor in the Highway Code. This has
now been partly rectified but is still not correct. Better luck next time!
Pedestrians with priority over turning traffic
The possibility of giving pedestrians a clear signalled priority without a
fully protected crossing was seen to have an enormous advantage in terms of
efficiency even back in the days when pedestrian facilites were only
provided at a minority of junctions and then only when criteria in terms of
number crossing and volume of the conflicting turning movement were met.
The London experiment was the result of TCUG/DfT discussions but was doomed
to failure. It was over-complex and tried to combine a period when peds had
protection and a period when they did not. A solution where the whole stage
ran flashing green to peds and flashing amber arrows to turning vehicles
would have been easier to understand and might have worked better.
The development of priority rather than full protection for peds in Europe
(particularly Germany) grew out of the principle that pedestrians were
legally obliged to obey signals and therefore needed signals to ALLOW them
to cross - not to give them guaranteed protection. The status of
pedestrians crossing side roads during a main road stage was seen as
equivalent to that of other straight-ahead "traffic". Turning traffic was
required to give way to them in the same way that in UK right turning
vehicles give way to oncoming traffic. Only when the numbers of turning
vehicles and pedestrians crossing the side road reached the point where they
could not be handled on a priority basis would a protected ped movement (or
should it be seen as a protected vehicle turning movement?) be provided.
In the "silly season" when senior officers and elected members returned from
their summer holidays, there were always questions of why, if the Germans
have ped signals at every junction, why can't we? Historically, the UK
position was that any set of signals was regarded as a "pedestrian facility"
in that it made breaks in the traffic flow, whether or not the were
pedestrian signals there. Turning traffic was required by the Highway Code
to give way to pedestrians but didn't in practice. In the 1980s it was
argued (by me at least!) that the the Highway Code rule should be encouraged
and if possible backed up by law and that, if ped indications were required,
flashing green and flashing amber arrow could be used. This was not
accepted and the continuing pressure for assistance to pedestrians has
resulted in only fully protected pedestrian facilities being acceptable.
This puts us in a very small minority in the world with virtually all of
Europe and the Americas (at least) accepting priority signalling in these
circumstances. I suspect the boat has now been missed in this matter - but
keep trying.
Red/amber
Red/amber was originally 3 seconds dropping to 2 seconds when new "advanced"
controllers were introduced with separate timing circuits for red/amber and
amber periods. It was useful initially to give time for dirvers to get the
heavy crash gearboxes into first before the green appeared. Where it is
used in Germany it is commonly now only one second long. We don't need so
long now to get into gear and two seconds with modern vehicles is quite long
enough for drivers to anticipate green. The complete dropping of red/amber
has been tried several times but always demonstrated an increase in lost
time which could then be offset with a reduction in intergreen. Overall
there was little avantage that would justify a change. Is it worth thinking
about reducing it to one second?
BUT why don't we insist on a red/amber against green conflict protection.
It is almost as dangerous as green/green and has caused many accidents in
the past.
Also, why do we still refer to red/amber as starting amber? I believe this
terminology was adopted in the late 1920s when signals went
red-amber-green-amber-red and it was necessary to distinguish between the
amber before green and the amber after green. Red/amber was introduced in
1929 since when it (or the more formal "red-with-amber") has been available
as an unambiguous and self-explanatory term for the period between red and
green.
Flashing amber all round
This has also been tried (also with flashing amber main road, flashing red
sie-road to give effectively a priority junction) but should not really be
necessary with good VA systems. It is valuable in countries where
fixed-time is the norm. However, I am sure that flashing amber is a safer
failure mode that signals out - even if it cannot be guaranteed to operate
in all circumstances (e.g. mains power failure) which is the usual reason
given for not allowing it.
Other Wacky Ideas
Unstaggered crossings
Now that we use near-sided ped indicators do we really need so many
staggered crossings? The see-through problems which prompted the use of
staggers can now be avoided. We could eliminate so many convoluted layouts
and unnecessary, unsightly guard railings if we didn't use staggers. As
before - other people in the world seems to manage.
Red arrows
The use of amber arrows continues to struggle on as a solution to confusion
with double headed signals. My preference has always been for the German
approach that would have a signal head with red, amber and green arrows
which clearly indicates, whatever display is showing, that this head
controls a turning movement. DfT have consistently maintained that a red
arrow is unacceptable as red signifies "stop" and an arrow signifies
movement and that stop should be unconditional. The German (and other
countries') interpretation is that a red arrow signifies that that movement
is not permitted. The Australians will show a red arrow with a full green
to show a held turning movement in the complete inverse of our red with
green filter arrow. Unfortunately, although this (to me) is easy to
understand, it is not part of the "language" of our signalling system and is
unlikely to be adopted.
European standardisation
It amazes me that when everything we use seems to be controlled by a
European standard, a thing so fundamental as the interpretation of signal
displays which affects millions of road users all over Europe as they visit
other countries, and which is highly safety related, is not only not subject
to international standardisation but that, as far as I know, there are no
effective discussions taking place to achieve any convergence. Perhaps TCUG
could take the lead in this by , as a first step, establishing links and
international discussion groups with user groups in other countries?
Final word
However good a wacky idea maybe or however well tried elsewhere, the final
killer argument in any discussion will always be - we have the safest
signalling system in the world: why change it?
David Overton
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