On Tue, 02 Aug 2005 16:43:40 -0000, (Mark Brader) wrote:

Tony Bryer writes:
Being a old guy who passed his test in imperial days the formula for
stopping distance was m(1+m/20) feet: the first term is basically the
distance travelled whilst your brain is getting your foot to press
the brake, the second [that travelled in] the actual time needed to stop.

However, that is an oversimplification. The distance needed to stop
under maximum braking force (or any particular force) varies as the
*square* of the speed.

Which is presumably why the quoted formula has an 'm squared' in it
(once you expand the brackets).

"Earl Purple" wrote in message
ups.com...
And actually, a road, if used properly, will usually take a greater
volume than a railway. On a D2 dual carriageway, for example, if cars
are travelling at a 2-second gap,

This assumes that all cars will leave this gap at all times. I try to
maintain a 100-150yd gap in front at all times, and more when travelling at
very high speeds.

In article ,
Tony Bryer wrote:
In article , Tom
Anderson wrote:
Then they're travelling too close together. Unless the traffic's
flowing at 40 mph, at which speed 2 seconds is almost enough.

Your arithmetic is wrong

Irrelevant (and arguable).

When using _your_ figure of 120 pax per minute per lane - which is
somewhat optimistic and assumes ideal conditions - you still get a
answer which says that a 3 lane motorway has the same capacity as
the central line.

It may be interesting to compare the projected cost of crossrail
with the projected cost of a 4 or 5 lane motorway over the same
route.

They would probably have equilvilent capacity according to your
figures; I'm assuming that crossrail capacity will be half as much
again as the central because it has longer trains, but that's a
somewhat back-of-the-envelope calculation.

--
Mike Bristow - really a very good driver

I (Mark Brader) wrote:
However, that is an oversimplification. The distance needed to stop
under maximum braking force (or any particular force) varies as the
*square* of the speed.

This response is posted:
Which is presumably why the quoted formula has an 'm squared' in it
(once you expand the brackets).

Awk! So it does. I'm not used to seeing it written that way, but
that's no excuse -- sorry, folks.
--
Mark Brader, Toronto | "Mark is probably right about something,
| but I forget what" -- Rayan Zachariassen

On Tue, 2 Aug 2005 18:31:12 +0000 (UTC), Mike Bristow
wrote:

When using _your_ figure of 120 pax per minute per lane - which is
somewhat optimistic and assumes ideal conditions - you still get a
answer which says that a 3 lane motorway has the same capacity as
the central line.

The fallacy in your argument is the comparison of cars with a full
train. You ought to be comparing 80-seat coaches with a train to get
the true figure. With a 2-second interval, that is a coach every 176
feet at 60 mph or about 4 coach lengths. If you can get that density
of seating (not seated and standing) on your train, you will be doing
very well.
--
Terry Harper
Website Coordinator, The Omnibus Society
http://www.omnibussoc.org

Earl Purple wrote:
Dave Arquati wrote:

No, no, no, please, no, to all of that. They planned to do it some time
ago (http://www.btinternet.com/~roads/lon...ringway1.html).


I know about the planned ringway. I don't think they should go ahead
with the whole of that though.


Of course, the Westway was a roaring success for the residents of the
area it cut through.


Are you sure? Traffic has always headed into London from the West and
it would do so without the A40 and the elevated M4, probably on the A4
instead, so the Cromwell Road, with its museums and hotels would simply
be totally choked. And those who don't use the A4 would use the A4020
(much of which used to be the A40) passing through Ealing etc. even
though they have intention to go to Ealing, whilst conflicting with
local traffic.

I was talking about the effect on people who lived in the residential
area through which the Westway was constructed.

Nevertheless, yes, traffic heads into London from the West - but without
the Westway, less may have done so. Traffic congestion acts as a
restraining mechanism.

The Western Avenue and the elevated Westway should be considered
separately as I believe the Western Avenue was constructed somewhat
earlier than the elevated Westway.

The little bit of the West Cross Route that comes South off the A40 is
a fairly useless road - it's good down to Shepherds Bush then takes you
through residential roads that were never meant to be a highway. Going
Northbound, if you want to continue North you have to take A40 and A406
or work your way through the local areas of Harlesden and Neasden. Its
only real purpose is as a relief road for Wood Lane.

To be fair to it, it allows traffic to avoid Shepherd's Bush Green
(although, yes, it dumps the significant proportion onto Holland Road).

These urban motorways only serve to generate new car traffic

Maybe a little but most of it will just be diverted off other roads.
For example someone coming from Portsmouth heading North may well go up
the A3, onto this road and subsequently the M1 rather than using the
Western stretch of the M25. Certainly those who live in Kingston going
North are more likely to use it. But are these people going to
specifically make more journeys by car just because the road is there?

Yes. That's not really a point up for debate - research is available all
over the place proving that new roads generate significant levels of new
traffic. I doubt that someone coming from Portsmouth heading north would
divert from the M25 via inner west London, although M25 congestion might
force them to do so - which would be extremely bad for the residents of
West London, who would then have to put up with long-distance traffic
passing through their area (the motorway may be segregated, but the
pollution and noise wouldn't be).

The obvious example of traffic generation is the M25. Many people make
more journeys by car specifically because the M25 is there - it has
encouraged a vast number of orbital commutes which never existed before
it was built. An urban motorway, similarly, would encourage people to
make a car-based commute (or other journey) across inner London where
they wouldn't have done so before.

If they want to encourage more people to use trains then improve the
railways too.

Limited funds are available, and railway and motorway projects are both
extremely expensive. It's one or the other, and the project which
increases car journeys significantly is not likely to win. "They" should
definitely improve railway (and other public transport) connections -
but they shouldn't start building urban motorways.

(whether tunnelled or not), and are also incredibly expensive
particularly if tunnelled).

It's more expensive to build a tunnel than a bridge but it does mean
they don't have to buy up land and compulsory purchase orders may
obviously cost more.

Either way, it's very expensive, with new road costs now in the many
millions of pounds per kilometre.

Talking of cost though, do you know how much revenue is lost everyday
through traffic queues?

Firstly, since a new road will generate new traffic that surrounding
roads will have to absorb, a new road project is only likely to cut
traffic queues on certain parts of the network for a certain number of
years before the situation worsens again (see the M25 and associated
widening projects).

Secondly, when factoring in revenue lost through congestion, it's time
to start factoring in the increased cost of pollution-related illness
and disbenefits and road accidents, as well as the less-easily
quantifiable social exclusion and general environmental effects.

And actually, a road, if used properly, will usually take a greater
volume than a railway. On a D2 dual carriageway, for example, if cars
are travelling at a 2-second gap, you get 30 cars in each lane passing
per minute. If each car has 2 occupants, that's 120 passengers a minute
in each direction. You'd need to run a very frequent train service to
carry that many.

Other people are debating the truth in that, but, as always, junctions
often limit capacity on a network, and urban motorways will have plenty
of those. In addition, although a smaller point, it's worth noting that
the road capacity as described is only available to those with access to
a car, whereas rail capacity is (theoretically) available to all.

Anyway, they were supposed to be raising all this money to improve
roads through the congestion charge but all I've seen is totally
unnecessary roadworks on roads that aren't broken. But then we know Ken
is anti-car.

The congestion charge raises money to fund public transport
improvements, not the roads.

Which is thankfully why you'll
never see a grade-separated South Circular any time soon.

Do you live and drive in the South of London?

Nope... but I lived next to a motorway for 18 years, and I wouldn't wish
it upon anyone. I live in the west of London (which already has urban
motorways, one of which is extremely close to my home), but I don't
drive (and neither do a large number of people in this are) - and
therefore I get a rather disproportionate share of the disbenefits of
urban motorways compared to the benefits.

--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London

Dave Arquati wrote:
I was talking about the effect on people who lived in the residential
area through which the Westway was constructed.

I don't know about then but taking Portobello Road as an example (the
Westway runs close). Has it had a negative effect on that road or will
the extended CG zone have a worse effect?

Yes. That's not really a point up for debate - research is available all
over the place proving that new roads generate significant levels of new
traffic. I doubt that someone coming from Portsmouth heading north would
divert from the M25 via inner west London, although M25 congestion might
force them to do so - which would be extremely bad for the residents of
West London, who would then have to put up with long-distance traffic
passing through their area (the motorway may be segregated, but the
pollution and noise wouldn't be).

Now what journey would you now make in a car on the M25 that you could
otherwise make on public transport? There is a railway line on the
"West Cross Route" that goes from Clapham through Kensington up to
Willesden, and there's another line that goes to Harrow. Now if they
improved the service on those lines and made them better known (they
don't appear on underground maps) then more people might consider using
them.

The obvious example of traffic generation is the M25. Many people make
more journeys by car specifically because the M25 is there - it has
encouraged a vast number of orbital commutes which never existed before
it was built. An urban motorway, similarly, would encourage people to
make a car-based commute (or other journey) across inner London where
they wouldn't have done so before.

And before the M25 was built, there was much higher unemployment. And
part of this is also caused by house prices continuing to rise thus
forcing people to live further away from their place of work and make a
longer commute. People move jobs far more frequently than they used to
and can't always find a job close to home (much that we'd like to). New
industrial estates open just off these motorways because they are now
easier to get to, and land is cheaper there.

As a result, many businesses have moved out to these business parks,
they have a lot of car-parking and very poor public transport
facilities. Car-pooling would be ideal but impractical if people don't
actually start and finish work at exactly the same time each day.
However it may certainly be the way to go.

Limited funds are available, and railway and motorway projects are both
extremely expensive. It's one or the other, and the project which
increases car journeys significantly is not likely to win. "They" should
definitely improve railway (and other public transport) connections -
but they shouldn't start building urban motorways.

But roads are not just limited to cars - buses and lorries also use
them. Railways are not so environmentally friendly either, as you need
electrification and normally that means overhead cables. You need far
more land. Crossing them is much harder, and generally they can take
you only to one place.

Either way, it's very expensive, with new road costs now in the many
millions of pounds per kilometre.

Good investment though. It cost a lot of money to build the GWR too,
but now as a result we have it.

Firstly, since a new road will generate new traffic that surrounding
roads will have to absorb, a new road project is only likely to cut
traffic queues on certain parts of the network for a certain number of
years before the situation worsens again (see the M25 and associated
widening projects).

If the road is good then there'll be no need for rat-running. But it
may generate more business in the area (as it will be easier to get
access) so more business will open, more superstores, etc, and you may
get people leaving the main road to use the facilities.

Secondly, when factoring in revenue lost through congestion, it's time
to start factoring in the increased cost of pollution-related illness
and disbenefits and road accidents, as well as the less-easily
quantifiable social exclusion and general environmental effects.

But the optimal speed for reducing pollution is 56mph. Going through
urban streets at an average of 12mph stop/start is thus very much more
polluting.


Other people are debating the truth in that, but, as always, junctions
often limit capacity on a network, and urban motorways will have plenty
of those. In addition, although a smaller point, it's worth noting that
the road capacity as described is only available to those with access to
a car, whereas rail capacity is (theoretically) available to all.

But if they also ran buses on those routes that would also be available
to all.

The congestion charge raises money to fund public transport
improvements, not the roads.

which seems to be more silly bus routes, carrying 8 passengers or so,
going down narrow roads totally inappropriate for a bus, stopping
everytime something comes the other way, still very poor service come
6-7pm (when many are still commuting home from work).

I'd rather see more express bus routes, infrequent stops, going along A
roads, particularly primary ones (generally more orbital).

Nope... but I lived next to a motorway for 18 years, and I wouldn't wish
it upon anyone. I live in the west of London (which already has urban
motorways, one of which is extremely close to my home), but I don't
drive (and neither do a large number of people in this are) - and
therefore I get a rather disproportionate share of the disbenefits of
urban motorways compared to the benefits.

I live close to the end of the M1 and close to where the A406 meets the
A1 and the A41 is also close by so I am surrounded by primary dual
carriageways. That actually makes car travel fairly convenient (while
the Northern Line is useful only if you want to go to Central London or
to Edgware). Most of the residents would prefer to see the old plans of
the A406 tunnel go ahead. I think it would be satisfactory simply to
have the A406 connect at both ends of the A1 via a tunnel without any
other tunnel links at all - it would at least reduce a vast amount of
the traffic at that junction.

I worked as a minicab driver for about 18 months between July 2002 and
the end of 2003.

On Tue, 2 Aug 2005, Tony Bryer wrote:

In article , Tom
Anderson wrote:

Then they're travelling too close together. Unless the traffic's
flowing at 40 mph, at which speed 2 seconds is almost enough.

Your arithmetic is wrong in that during the period you are stopping your
average speed is only going to be about half the initial speed, so you
would need to double your calculated times.

No, that's irrelevant - HC rule 105 sayeth that "the safe rule is never to
get closer than the overall stopping distance"; that applies to cars that
are cruising at constant speed, in which case my calculations are correct.
The stuff about average speed during braking is captured in the
calculation of that overall stopping distance.

What you ignore, and what lies behind the 2 second rule on faster roads
with good visibility is that the car in front is not going to stop dead
- unless something really catastrophic happens.

True, but whoever wrote the HC didn't seem to think that mattered - rule
105 commands you to "drive at a speed that will allow you to stop well
within the distance you can see to be clear". Perhaps they had those
really catastrophic somethings in mind?

tom

--
No hay banda

On Tue, 2 Aug 2005, Terry Harper wrote:

On Tue, 2 Aug 2005 18:31:12 +0000 (UTC), Mike Bristow
wrote:

When using _your_ figure of 120 pax per minute per lane - which is
somewhat optimistic and assumes ideal conditions - you still get a
answer which says that a 3 lane motorway has the same capacity as the
central line.

The fallacy in your argument is the comparison of cars with a full
train. You ought to be comparing 80-seat coaches with a train to get the
true figure.

Wrong. We're not talking about idealised fantasy busways here, we're
talking about transport corridors as they are found in the wild -
motorways really are full of cars carrying an average of ~1.5 people each,
and tube lines really are full of trains carrying 500 people each (the
620 pax/train number i used is the planned capacity; actual passenger
loads are actually even higher than that).

With a 2-second interval, that is a coach every 176 feet at 60 mph or
about 4 coach lengths. If you can get that density of seating (not
seated and standing) on your train, you will be doing very well.

Well, if you're going to start running 1800 bph with every seat full, i
hope you don't mind if i increase the frequency of my trains to something
equally ludicrous to maintain my lead .

tom

--
No hay banda

In article ,
Tom Anderson wrote:
No, that's irrelevant - HC rule 105 sayeth that "the safe rule is never to
get closer than the overall stopping distance"; that applies to cars that
are cruising at constant speed, in which case my calculations are correct.
The stuff about average speed during braking is captured in the
calculation of that overall stopping distance.

If we're to play with real-world numbers, throwing the HC out the
window would be the best bet. I think that a gap of 2 seconds
between vehicleS is reasonable (ie, 30 cars per minute per lane).

--
Mike Bristow - really a very good driver