"Dominic" wrote in message
om...
In article ,
Tom Anderson wrote:
What's the point of trams?

I'm not having a go, i just don't really understand what's so great
about
them. Not from the heavy rail side (they're obviously much cheaper
and
more flexible, whilst smaller and slower), but from the bus side.

Yeah, why do we need trams? Here's my opinion - feel free to criticise
it:

1. Buses are as fast as trams - even with diesel engines. If Croydon
trams ran long sections on the road mixing with cars, or if London
buses ran on a proper network of properly enforced bus lanes, that
would become clear. The maximum acceleration of both buses and trams
is set by passenger comfort - I reckon both can reach that maximum.

While it is possible to design a bus with an engine that would give it such
performance, this is not done because the size, weight, initial cost and
increased fuel consumption of such a large engine increases the operating
and capital costs without enough of a gain in performance for such
technology to be justified. The nature of electric traction is such that it
can be run at significantly higher than its maximum continuous power rating
for a short period of time quite safely. This is very useful for
accelerating rapidly and then maintaining that constant speed for a longer
period.

2. Buses can easily rival trams at shifting passengers - just 2 of
these 180 passenger Van Hool double-artic buses carry more than a
Croydon tram:

http://www.vanhool.com/products_bus_...Categ oryID=1
They're a bit unwieldy, but so would Croydon trams be if they really
had to mix with the traffic!

The confinement of a tram to the fixed swept path of the tramway makes them
considerably more controlable in the sort of tight spaces encountered in
London than such a bus. There is no guarantee that the middle and rear
portion of the bus in that photograph will follow the same swept path as the
front. Anecdotal evidence suggests that even with single articulated buses,
there are problems arising from this. If you look at the way articulated
buses attempt to pull over at a stop, you will see that they almost
invariably end up with the front half pulled over and the rear still
blocking the carriageway.

3. Buses ride just as well as trams, if you put them on a well
surfaced road. Both can suffer from harsh braking when mixing with
cars and pedestrians. There's nothing wrong with rubber tyres - they
allow you to apply greater tractive and braking forces. That's why
many Paris Metro trains have them.

With magnetic track brakes as applied to all trams built for decades, the
braking force available to a tram (the rate of deceleration possible) is
appreciably greater than that possible with rubber tyres on tarmac. Buses
only ride well if they run on a well maintained road. As the bus companies
do not maintain their own roads, they tend to run on ill maintained roads.
Trams ride well on well maintained track, but as tram tracks belong to the
tram company, they tend to be well maintained. Acceleration of buses and
trams is not limited by friction but by the power of the engines. The
torque characteristics of an electric motor and their ability to overload
means that, if they want to, they can out-accelerate just about any diesel
engined bus at normal street conditions. So that's wrong on all these
counts.

4. Diesel buses are more environmentally friendly than electric trams.
Although buses produce more pollution at the point of use, trams
produce more pollution overall - the electricity they run on has to be
produced somewhere, and it's been through a lot of inefficient energy
conversions by the time it reaches the tram.

If you consider the full energy chain for each, you will see this is not the
case. First of all, the rolling resistance for a tram is a fraction of that
for the same weight of bus. Weight for weight, trams carry significantly
more passengers because electric motors are much lighter than diesel
engines, and they carry no fuel. This means that per passenger, they use
less energy to move about. Because of the higher efficency of large power
stations, and the relatively high efficiency of the national grid, per unit
energy from combusted fuel to point of use at wheel tread, there is a slight
advantage to buses, but this is of the order of about 5%, while the benefits
of steel wheel and electric traction are more likely to be of the order of
20% on a per passenger basis. If you then consider the energy requirements
to get fuel from where it comes out of the ground to the location of
consumption, and any refining process, you find that diesel fuel is
substantially worse off there (coal and natural gas require no refinenemt
for use in a power station, and nuclear fuel is used in such tiny quantities
for the energy released, these costs are minute in energy terms).

The common fallacy you are falling victim to is considering only the
thermodynamic efficiency from combustion to power at the wheel tread, not
looking at the power demands, or the requirement to get the right fuel to
the point of combustion.

5. Buses could have the "wow factor" and desirability of trams, if
they were made to look more exciting. Designs like the Wright Eclipse
Gemini are heading in the right direction.

But buses will always lack the permanent advertisement of their route
provided by the fixed infrastructure. If I look at the road in front of my
house, there is no evidence that there are two bus routes down it. If there
were a tramline down the road, there would be.

6. One final point - buses require no fixed infrastructure to be built
on their route. You can run them on the road - brilliant! If there are
roadworks, you drive around them!

Wrong again. you can't run a bus over a field, you need some fixed
infrastructure called a road. To give the bus adequate reliability, you
need more infrastructure such as a bus lane. If nothing but buses use the
bus lane ever, then the costs of maintaining that bus lane must be
attributed to the bus services that use it. the point services are diverted
from under tramways is so that there *aren*t roadworks on the tram's path.

Robin

In article , Robin Payne wrote:

"Dominic" wrote in message
om...

5. Buses could have the "wow factor" and desirability of trams, if
they were made to look more exciting. Designs like the Wright Eclipse
Gemini are heading in the right direction.

But buses will always lack the permanent advertisement of their route
provided by the fixed infrastructure. If I look at the road in front of my
house, there is no evidence that there are two bus routes down it. If there
were a tramline down the road, there would be.

Well, you *do* have the bus stop signs and (in at least some cases)
shelters. (Excepting 'hail and ride' areas, which, though rare in G.
London, do occur. I ride through one every morning)

These are certainly enough for me to notice when I'm on a street or
road, though I'll readily grant they're not nearly as prominent as a
tram line would be. Also, I rely on public transport to a greater extent
than most people, so it's possible I also notice bus infrastructure more
readily than most.

And I have to say to Dominic's point that while it's possible to make
buses look more attractive, swoopy and futuristic, I strongly agree with
the counterarguments made in various places in this thread about road
quality, fossil-fuel engines yielding vibration, noise and fumes, etc.

The mere facts of all the twisting and turning through urban traffic,
pulling into and out of bus stops, etc, also tend to detract from the
comfort of the ride, at least for me, such that I cannot imagine buses
achieving the ride comfort level of rail vehicles.

Niklas
--
"Forget the damned motor car and build cities for lovers and friends."
-- Lewis Mumford
http://www.carfree.com/

"Robin Payne" wrote in message ...

Snipped - some great points from Robin

4. Diesel buses are more environmentally friendly than electric trams.
Although buses produce more pollution at the point of use, trams
produce more pollution overall - the electricity they run on has to be
produced somewhere, and it's been through a lot of inefficient energy
conversions by the time it reaches the tram.

If you consider the full energy chain for each, you will see this is not the
case. First of all, the rolling resistance for a tram is a fraction of that
for the same weight of bus. Weight for weight, trams carry significantly
more passengers because electric motors are much lighter than diesel
engines, and they carry no fuel. This means that per passenger, they use
less energy to move about.
All good points.
Because of the higher efficency of large power
stations, and the relatively high efficiency of the national grid, per unit
energy from combusted fuel to point of use at wheel tread, there is a slight
advantage to buses, but this is of the order of about 5%, while the benefits
of steel wheel and electric traction are more likely to be of the order of
20% on a per passenger basis. If you then consider the energy requirements
to get fuel from where it comes out of the ground to the location of
consumption, and any refining process, you find that diesel fuel is
substantially worse off there (coal and natural gas require no refinenemt
for use in a power station, and nuclear fuel is used in such tiny quantities
for the energy released, these costs are minute in energy terms).

The common fallacy you are falling victim to is considering only the
thermodynamic efficiency from combustion to power at the wheel tread, not
looking at the power demands, or the requirement to get the right fuel to
the point of combustion.

Am I? Neither the bus nor the power stations is sited where the fuel
is extracted. Fuel needs to be transported to power stations as well.
Sure, road tankers burn diesel to transport diesel to bus garages, but
gas pipelines burn gas to pump gas (using in line turbines), and coal
trains burn diesel to move coal.

I'm very impressed by your figures. I've was arguing the case for
diesel buses, and I don't intend to move the goal posts, but buses can
also be fueled on Compressed Natural Gas (CNG). This would use the
same fuel that's providing about 40% of our electricity, which trams
use, and it avoids the inefficiencies of the refining process needed
for diesel (which is drawing so much criticism! I hate the greasiness
of the fuel!). The gas could even reach the buses by pipeline.

Many fleets of CNG (and also LPG) buses are in operation worldwide,
particularly the US, but I don't think there's any in this country?
They use normal bus diesel engines, but modified to spark ignition.
Much lower emissions can be achieved. I can't believe no comparative
diesel vs. CNG vs. LPG trials have been done in London. At least we're
doing fuel cell!

What do readers here think about it?

See http://www.cleanairnet.org/infopool/...lue-17726.html
for info about different bus fuels. Cheers,

Dominic

"Dominic" wrote in message
om...
"Robin Payne" wrote in message
...

Snipped - some great points from Robin

[more snipped]

I'm very impressed by your figures. I've was arguing the case for
diesel buses, and I don't intend to move the goal posts, but buses can
also be fueled on Compressed Natural Gas (CNG). This would use the
same fuel that's providing about 40% of our electricity, which trams
use, and it avoids the inefficiencies of the refining process needed
for diesel (which is drawing so much criticism! I hate the greasiness
of the fuel!). The gas could even reach the buses by pipeline.

Mind has just boggled at the thought of pipelines buried in a conduit along
bus routes, with a sort of plough arrangement under the bus, opening a
leather flap on the top of the pipe, to allow the bus to draw its fuel from
the pipe .......

) ---------- (look!!)


Many fleets of CNG (and also LPG) buses are in operation worldwide,
particularly the US, but I don't think there's any in this country?
Sarfampton. Slow. Top heavy. Can hardly get up Lancers Hill. Run out of
gas halfway through the day.

They use normal bus diesel engines, but modified to spark ignition.
Much lower emissions can be achieved. I can't believe no comparative
diesel vs. CNG vs. LPG trials have been done in London. At least we're
doing fuel cell!

What do readers here think about it?

If you intend putting those great big tanks on top of the bus, why not put a
couple of trolley arms on top, instead, running under fixed wiring, and
driving a cleaner electic motor? Quieter, better acceleration, more
efficient braking (regenerative - feeds back into the overhead supply.)

"Dominic" wrote in message
om...

Many fleets of CNG (and also LPG) buses are in operation worldwide,
particularly the US, but I don't think there's any in this country?

There are both in operation in a number of places.
http://www.liverpoolcollege.org.uk/Mosaic/natural.htm will show you some on
Merseyside.

Guide Friday ran many of their tour buses on LPG.
--
Terry Harper, Web Co-ordinator, The Omnibus Society
75th Anniversary 2004, see http://www.omnibussoc.org/75th.htm
E-mail:
URL: http://www.terry.harper.btinternet.co.uk/

"Ian Henden" wrote in message
...

What do readers here think about it?

If you intend putting those great big tanks on top of the bus, why not put
a
couple of trolley arms on top, instead, running under fixed wiring, and
driving a cleaner electic motor? Quieter, better acceleration, more
efficient braking (regenerative - feeds back into the overhead supply.)

My opinion is that trams are better than (trolley) buses chiefly because of
their carrying capacity. Bendibuses get closer to their carrying capacity
but this is still no match for a 3 section tram? Also, running on rails,
don't trams use less energy than their trolleybus counterparts? The
trolleyarm itself is tedious; two arms are needed and they might come off
the wire. A tram with a pantograph and returning the supply through the
rails seems much simpler.

Ian Henden wrote in message If you intend
putting those great big tanks on top of the bus, why not put a
couple of trolley arms on top, instead, running under fixed wiring, and
driving a cleaner electic motor? Quieter

Ian,
The Skoda trolleys in Usti-Nad-Labem in CZ were far from quiet when "ticking
over" at the terminus outside my hotel
The trolley service in Usti is 24 hour.

I have some excellent brochures from Usiti's tram centenary for sale
(well-illustrated but text is in Czech).

Regards
Dave Farrier
www.daveandpat.freeserve.co.uk

"Dominic" wrote in message
om...
"Robin Payne" wrote in message
...

Snipped - some great points from Robin

4. Diesel buses are more environmentally friendly than electric trams.
Although buses produce more pollution at the point of use, trams
produce more pollution overall - the electricity they run on has to be
produced somewhere, and it's been through a lot of inefficient energy
conversions by the time it reaches the tram.

If you consider the full energy chain for each, you will see this is not
the
case. First of all, the rolling resistance for a tram is a fraction of
that
for the same weight of bus. Weight for weight, trams carry significantly
more passengers because electric motors are much lighter than diesel
engines, and they carry no fuel. This means that per passenger, they
use
less energy to move about.
All good points.
Because of the higher efficency of large power
stations, and the relatively high efficiency of the national grid, per
unit
energy from combusted fuel to point of use at wheel tread, there is a
slight
advantage to buses, but this is of the order of about 5%, while the
benefits
of steel wheel and electric traction are more likely to be of the order
of
20% on a per passenger basis. If you then consider the energy
requirements
to get fuel from where it comes out of the ground to the location of
consumption, and any refining process, you find that diesel fuel is
substantially worse off there (coal and natural gas require no
refinenemt
for use in a power station, and nuclear fuel is used in such tiny
quantities
for the energy released, these costs are minute in energy terms).

The common fallacy you are falling victim to is considering only the
thermodynamic efficiency from combustion to power at the wheel tread,
not
looking at the power demands, or the requirement to get the right fuel
to
the point of combustion.

Am I? Neither the bus nor the power stations is sited where the fuel
is extracted. Fuel needs to be transported to power stations as well.
Sure, road tankers burn diesel to transport diesel to bus garages, but
gas pipelines burn gas to pump gas (using in line turbines), and coal
trains burn diesel to move coal.

A typical coal train in the UK would haul about 1,100 tons of coal using a
single 3000hp locomotive (2.72 hp/ton). This compares with an articulated
lorry with a useful payload of about 40 tons, which would require about 500
hp to draw it (12.5 hp/ton). As the diesel engines used in both are of
similar capacity, in order for a truckload of diesel fuel to be a more
efficient means of transporting energy than a trainload of coal, diesel
would have to contain about 6 times as much energy per unit mass compared
with coal. This is of course not the case. Similar applies to natural gas,
but I haven't figure sto hand to demonstrate this. This is before you
consider the extra energy consumption in the oil refining process that coal
need not go through.

I'm very impressed by your figures. I've was arguing the case for
diesel buses, and I don't intend to move the goal posts, but buses can
also be fueled on Compressed Natural Gas (CNG). This would use the
same fuel that's providing about 40% of our electricity, which trams
use, and it avoids the inefficiencies of the refining process needed
for diesel (which is drawing so much criticism! I hate the greasiness
of the fuel!). The gas could even reach the buses by pipeline.

The added wieght to the bus of the handling facilities for CNG just go to
make the efficiency of the bus even worse as you have even more weight to
cart about on the bus that isn't paying passengers. Gases are dreadful
fuels to transport by vehicle because of thier increadibly low densities at
ambient temperature and pressure. If you are going to use gas as a fuel,
the only sensible way to use it is to burn it at a fixed location and
transmit the energy.

You also need to consider that natural gas can be used in the most efficient
(combustion based) power stations in the world, the combined cycle, which
can offer 50-60% thermodynamic efficiency, against 30-40% of a piston engine
in a bus. This means that the power transmission system would have to be
about 65% efficient for the two to be thermodynamically equal. This is not
the case, the national grid is close to 95% efficient, and the substations
and transmisions for a tramway will bring this down somewhat, but not to
65%. This is before you consider the reduced power requirement of a lighter
weight vehicle that need not carry a large pressure vessel on its roof, or a
diesel engine (heavy chunks of metal, they are) underneath it.

Many fleets of CNG (and also LPG) buses are in operation worldwide,
particularly the US, but I don't think there's any in this country?
They use normal bus diesel engines, but modified to spark ignition.
Much lower emissions can be achieved. I can't believe no comparative
diesel vs. CNG vs. LPG trials have been done in London. At least we're
doing fuel cell!

What do readers here think about it?

See http://www.cleanairnet.org/infopool/...lue-17726.html
for info about different bus fuels. Cheers,

I don't see how using a different fossil fuel in a piston engine will make a
significant difference to the bus. It will never be as good as a tram in
energy terms as long as:
1) it carries its fuel about with it too
2) it runs on pneumatic tyres on concrete (consider why the power to weight
ratio of a coal train and a lorry are so different).

Interesting website, but it misses the most efficient bus out there
http://www.transport-of-delight.com/...olleybus-1.jpg

Robin

On Mon, 05 Apr 2004 20:53:35 +0100, Robin Payne wrote:

Interesting website, but it misses the most efficient bus out there
http://www.transport-of-delight.com/...olleybus-1.jpg

Yes, but...

1) If you're putting all that fixed infrastructure up you may as well pay
the extra trams would cost for the massive extra benefit - certainly in
the UK where they'll attract a much larger ridership - and one that'll
likely be willing to pay higher fares. Sure, dual-power exists, but then
you're lugging an engine and fuel (or batteries) around as well.

2) Are they *really* much more efficient, taking into account transmission
losses and the fact that fossil fuels will probably generate the
electricity anyway? Perhaps they made sense when nuclear seemed to be the
way forward - but does that stand now much of the UK's power generation is
natural gas?

Neil
--
Neil Williams in Milton Keynes, UK
Mail me on neil at the above domain; mail to the above address is NOT read

"Neil Williams" wrote in message
news
On Mon, 05 Apr 2004 20:53:35 +0100, Robin Payne wrote:

Interesting website, but it misses the most efficient bus out there

http://www.transport-of-delight.com/...VancouverTroll
eybus-1.jpg

Yes, but...

1) If you're putting all that fixed infrastructure up you may as well pay
the extra trams would cost for the massive extra benefit - certainly in
the UK where they'll attract a much larger ridership - and one that'll
likely be willing to pay higher fares. Sure, dual-power exists, but then
you're lugging an engine and fuel (or batteries) around as well.

2) Are they *really* much more efficient, taking into account transmission
losses and the fact that fossil fuels will probably generate the
electricity anyway? Perhaps they made sense when nuclear seemed to be the
way forward - but does that stand now much of the UK's power generation is
natural gas?

The benefit of using electricity is that the method of producing it can be
changed with no direct cost or operational inconvenience to the user. I do
accept that prices may well rise due to the additional capital expenditure.