On Thu, 10 Nov 2005 10:02:33 +0000, "Clive D. W. Feather"
wrote:

In article , David Bradley
writes
High speeds are not likely to be a problem along the Uxbridge Road (the
proposed mean speed for the tramway is 13 M.P.H.!).

Is this mean speed while running, mean speed calculated start-to-stop,
or mean speed from end point to end point? There's a huge difference
between these.

For example, consider a route 10km long with 29 intermediate stops (that
is, a stop every 333m), assume that the dwell time at stops is 30
seconds, and that trams can accelerate and brake at 2m/s^2. I'll use
5m/s (11.2mph) for ease of calculation:

* End-to-end speed of 5m/s means end-to-end time of 2000 seconds (just
under 35 minutes).
* 870 seconds is spent stopped, so that's 1130 seconds of running time,
or just under 38 seconds between stops. That's a start-to-stop speed of
8.85m/s (19.9mph).
* This requires accelerating to 10m/s (22.5mph), running at that speed
for 28 seconds, then decelerating again.

So the end-to-end speed is only half the service speed.

There is
no experience whatsoever of 40 metre trams in UK streets, so we have no
knowledge of how they will fare even with their fixed path.

There is experience with coupled pairs in Manchester and even Blackpool.
We also have hundreds of years of experience of rail transport which
shows us that all the vehicles follow the same fixed path, whether the
combination is 5 or 500m long.

It is unfortunate that all this nit picking continues with statements that I
make concerning the viablity of tramway services along the Uxbridge Road.
Responses to inaccurate statements, such as made here, have to be challeged
before they become folklore. I would really prefere to actively persue
development of my web site www.tfwl.org.uk where true facts are given
following the most detailed research, as far as time permits, in anything that
is said there.

So you don't like the statement that mean speed for the tramway is quoted as
13 MPH. Well various TfL reports give the overall jourrney time from Uxbridge
to Shepherd's Bush (20 km.) of around an hour and the mean end to end speed
(thus including stops) of 19 or 20 k.p.h. (depends on which report!). I have
(slightly generously) approximated this to 13 m.p.h.

Clearly the vehicles should be able to exceed this between stops but it is
unlikely that they will exceed 30 m.p.h. ( 48 k.p.h.) in doing so and in many
places they will going far slower. They will have no opportunity for 'high
speed' running of 50 m.p.h. (80 k.p.h.) which Croydon Tramlink achieves on
many sections.

Manchester is essentially railway branches joined together with very limited
street running in between and a small section at the end of the Eccles Line.
Blackpool is not on-street either except for a part at the Fleetwood end. The
point is that the Uxbridge Road is **ALL** street and of course as all the
information reminds us, a very congested street at that.

The issue is not that of the path of the tram. That is clearly defined by the
rails, as stated, The question is how you can fit the 40 metre length in the
street between junctions, tram stops, stationary traffic of one sort or
another, traffic 'nipping in' etc. Even with the flexibility of path available
(by steering) of a bus, 'bendies' on London routes often have to be guided
very carefully to be able to be squeezed into the available road space and
these are 18 metres long. The tram has to occupy 40 metres of carriageway at
any time. I believe that to get a clear 40 metres along some of the more
heavily congested sections of this road, may at many times prove difficult and
the tram will be delayed not because other traffic has stopped, but because of
its own size. A good analogy would be that of artic lorries which are often
unable to proceed even when other traffic is moving because there simply is
not enough carriageway into which they can fit. the tram will of course be
over twice the length of any artic lorry.

This sort of problem can be experienced daily (only to a lesser extent as the
trams are shorter than 40 metres) in those cities with extensive street
running of their trams and congested streets such as Turin for example.

David Bradley