The documentation is now in pdf format:
www.cyberpictures.net/wlt.pdf amd so those that were nervious about
downloading a MS Word document should be happier with this format. I
appreciate the efforts made by Colin Rosenstiel to bring this happy
state of affairs about.

Meanwhile with the help of my friend I would like to give a response
to Dave Arquati at Imperial College. Colin Mackenzie points out more
fallacies and doesn't know about kerb guidance. He might have a point
about decelleration though. So here is what we feel is an appropriate
response. If you have not the time or inclination to read on further,
now is the time to move onto other topics in this news group.

It is felt that the reduced speed approach problem quoted is more
theoretical than practical in reality. Clearly to get real answers to
the traffic flow difficulties associated with both the 3 minute 40
metre tram option with banned turns and the 2 minute
25 metre trolleybus option with permitted turns requires some very
complex traffic flow mathematics and is best done with suitable
computer simulations. If TfL were really interested in checking out
various options in an honest and open manner, such simulations could
be easily arranged using one of a number of reputable suppliers.

Having no access to such simulations, nor the funds to purchase same,
I give some approximations of what might occur using much simpler
approximated mathematical models.

If we assume that the road traffic flow is 30 m.p.h. (around 12
metres/second) a tram will decelerate to rest at maximum service brake
force in around eight seconds. If we assume that the trolleybus has a
mean deceleration of one third less to gain the Kassel kerb (that
brings the deceleration rate down to around 1 metre per second squared
and is probably a much greater reduction than required in reality),
then the trolleybus will take 12 seconds. At first sight this appears
to give the tram an advantage in time of four seconds per stop but it
has to be remembered that the trolleybus has a very great advantage in
acceleration and although very high maximum accelerative rates are
quoted for modern trams, these are actually very theoretical and in
practice only apply on the level or downhill and with dry rails. If
there are any adverse adhesion conditions, the electronic control
systems compensate to prevent slipping and acceleration is actually
much less in practice than the theoretical maximum quoted. The
trolleybus with its rubber tyres on the road does not suffer the same
loss of traction (this of course is the reason for the rubber tyred
metros in Paris which have much higher accelerative rates in practice
than the conventional steel wheeled variety). So in practice the
trolleybus is not actually going to lose any time.

Now in respect of road space occupied and thus clearance behind the
vehicle the following applies. (For any mathematicians, the figures
that follow are based on linear extrapolations rather than using
integral calculus as I do not have the precise braking curves and the
difference will be too small to affect the overall results). The
trolleybus in its 12 second deceleration will traverse about 72 metres
whilst in the same 12 seconds the tram if able to go at full speed for
the first four seconds before deceleration will traverse 96 metres in
the same time. The difference is 24 metres less the 15 metre disparity
in length of vehicle and so equals 9 metres (nearly two car lengths).
This appears to suggest that the tram has an advantage (albeit slight)
but of course these figures are only true if the traffic is moving at
30 m.p.h. which would suggest clear road conditions with minimal
disruption.

If we assume a greater level of traffic such that the tram or
trolleybus can only approach at 20 m.p.h. (8 metres per second), then
the figures are very different. The tram now takes 5.5 seconds to
stop. Because of the lower speed approach, the trolleybus may now be
able to decelerate at the same rate as the tram, but even assuming the
same two thirds ratio as previously, the trolleybus will now take
around 8 seconds to stop. The difference now is that the tram has gone
about 42 metres whilst the trolleybus has gone about 32 metres. The
difference is 10 metres which is less than the 15 metre length
difference. This implies that the trolleybus now clears the road
behind quicker because of its lesser length and despite any lesser
decelerative rate.

So the conclusion appears to be that the tram is only advantageous in
clearing the road behind when entering a stop if the road is clear. If
the Uxbridge Road were likely to be clear, then of course there would
be much less debate about the whole scheme. The more congested the
road and thus the lower the mean speeds along the more congested
sections, the more advantage the shorter trolleybus has in this
respect. The trolleybus also has the capacity to manoeuvre in two
dimensions around congestion and/or stationary streams of traffic
waiting to turn. The tram has a one dimensional fixed path on its
track.

Combining the two, the only reasonable conclusion must be that the
trolleybus has the advantage in terms of congestion effects on other
traffic, when the traffic is already congested. The tram would only
have a theoretical advantage when there was little congestion and the
traffic was free flowing and thus therefore when such theoretical
advantage was of no practical value.

OK you can all leave the classroom now. Bye.

David Bradley

Has the hybrid rubber-tyred tram as used in Nancy been considered ? This
would give the benefits of larger capacity whilst (presumably) being quieter
and having lower installation costs.
Cheerz,
Baz

On Sat, 13 Nov 2004 21:04:35 -0000, "Marratxi"
wrote:

Has the hybrid rubber-tyred tram as used in Nancy been considered ? This
would give the benefits of larger capacity whilst (presumably) being quieter
and having lower installation costs.
Cheerz,
Baz


For now at least, it has been discounted.

Unfortunately there have been major/minor teething issues with the
guidance system and therefore despite being potentially a very
attractive proposition it would be sensible to see an extended term of
reliable operation first, perhaps as much as five years. This puts it
outside the time frame for consideration for the Uxbridge Road transit
scheme.

David Bradley

"David Bradley" wrote in message
...

Converting the document into HTML format has resulted in the
presentation of many of the tables into a most unsatisfactory format.
They are corrupted so badly that the effort to manually tidy it all up
would be extensive. Perhaps converting to PDF format might be a
possibility, but I don't have that software.

Try www.pdf995.com for a free PDF printer driver.
--
Terry Harper
http://www.terry.harper.btinternet.co.uk/

In message , David Bradley
writes
A recent visit to the Nottingham system showed that the trams were
spacious and have comfortable seats. They have completely level flat
floors. On the negative side, the ride is awful, particularly on
curves where the vehicles seem to go round in crab fashion on a series
of straights rather than in an elegant curve. This jolts standing
passengers quite badly. The ride is far worse than Croydon, Machester,
Sheffield or Birmingham.
I felt the Nottingham ride to be fine. It's certainly better than that
on the street running section of the "Birmingham" system (actually in
Wolverhampton), which is quite poor with a lot of rail corrugation. Of
the other systems you mentioned, all of which I've ridden on in the
past, I would only have singled out Manchester as being poor overall and
that was quite some time ago so things might have changed.

(I've also not done the whole of the Nottingham system, so maybe the
jolting you describe is in a particular position?)
--
Ian Jelf, MITG, Birmingham, UK
Registered "Blue Badge" Tourist Guide for
London & the Heart of England
http://www.bluebadge.demon.co.uk

On Tue, 23 Nov 2004 10:16:49 +0000, Ian Jelf
wrote:

In message , David Bradley
writes
A recent visit to the Nottingham system showed that the trams were
spacious and have comfortable seats. They have completely level flat
floors. On the negative side, the ride is awful, particularly on
curves where the vehicles seem to go round in crab fashion on a series
of straights rather than in an elegant curve. This jolts standing
passengers quite badly. The ride is far worse than Croydon, Machester,
Sheffield or Birmingham.
I felt the Nottingham ride to be fine. It's certainly better than that
on the street running section of the "Birmingham" system (actually in
Wolverhampton), which is quite poor with a lot of rail corrugation. Of
the other systems you mentioned, all of which I've ridden on in the
past, I would only have singled out Manchester as being poor overall and
that was quite some time ago so things might have changed.

(I've also not done the whole of the Nottingham system, so maybe the
jolting you describe is in a particular position?)


Probably fair to say the ride isn't too bad on the straight, it's
mainly on the sharp curves, of which there are quite a few on the
street running section and just north of it, but the ride is
definitely truly awful on those bits and has been independently
experienced by a couple of my friends, and it really is, for all of
us, a ride quality that is very much below par.

Like many enthusiasts, my group of friends visit those few trams
systems in operation in the UK only on an infrequent basis and
therefore our tram riding experiences are limited for in depth
comparisons to be made. However we have had in recent years all too
much experience of London diesel bus travel, in clapped-out vehicles
with shot suspension on poor road surfaces driven by unskilled and/or
or bloody-minded drivers, and the ride on the Nottingham curves
reminds us of that (minus the fumes and the engine vibration).

All these ills or so easily solved with trolleybus technology which is
explained at this URL: http://www.tbus.org.uk/faq.htm. The interest is
there for trolleybuses, judging by the number of requests for our
detailed analysis on the West London scheme which can be found at:
http://www.cyberpictures.net/wlt.pdf. This PDF has just been reloaded
and is now based on a conversion from the Word document using CutePDF
which has made a better job of the tables than the previous version.

David Bradley


David Bradley