OT: 20 & 30mph pollution differences

elyob said:

Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

He believes that the RPA is trying to close the park to all cars and
that the park is the main route for vehicles travelling between
Kingston and west London.[1]

He wants the RPA team retired and new 21st Century thinking people
brought in. I'm going to suggest congestion charge cameras which make
sure people obey the 20mph limits by averaging their time within the
park. Also, for anyone who uses it solely to 'cut-through' a £5
toll ... is that 21st Century enough?

Nick

[1] Funny, I thought the A3 was there for that reason.

A cyclist was killed by a killer speeding driver in Greenwich park
which incident may be influencing this decision.

elyob said:

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

That sounds like something I used to hear a lot (not so much now) that
generally, driving faster = less fuel used = less pollution (and
conversly, ... slower = more... = more...). The main argument seems
to be being able to drive in a higher gear.

My father has no problem driving in 5th gear in town traffic, so I
suspect it's a bit of a spurious argument.

PhilD

--
<><

elyob said:

He wants the RPA team retired and new 21st Century thinking people
brought in. I'm going to suggest congestion charge cameras which make
sure people obey the 20mph limits by averaging their time within the
park.

Don't you mean average speed cameras as fitted to many motorway road
works these days?

The one I really enjoyed was one of those Cannonball or similar rallys
across Europe where the French border guards informed each contestant as
they entered France that they had recorded their entry time and on
leaving France would calculate their average speed and confiscate the
vehicles if they had been going too fast. Worked a treat (to much
grumbling by contestants) but Schengen put an end to that form of
enforcement.

--
Tony

" I would never die for my beliefs because I might be wrong."
Bertrand Russell

PhilD said:

That sounds like something I used to hear a lot (not so much now) that
generally, driving faster = less fuel used = less pollution (and
conversly, ... slower = more... = more...).

Sounds like that old one of being low on fuel and having to drive fast to
get to the petrol station before it ran out ;-)

--
Tony

" I would never die for my beliefs because I might be wrong."
Bertrand Russell

"Tony Raven" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Sounds like that old one of being low on fuel and having to drive fast to
get to the petrol station before it ran out ;-)

I know people who have done that - one who was a reasonably respected
physics professor who knew it wouldn't help, but he did it anyway :-)

cheers,
clive

elyob said:

Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution,

Than what? Than driving at 30 mph?

Quoted message said:

he
doesn't back it up and wondered if there is any evidence to the
contrary?

He could be right. It depends upon your specific car and engine.

"The Slower Speeds Initiative" (of all people :-) ) suggest on their
website[1] that 44 mph is the optimum speed for the lowest emissions.
Presumably speeds below, as well as above, lead to higher CO2, and other
outputs.

I know that the gearing plays a part. Some cars would struggle to
cruise smoothly at 20 mph in top gear (where they may manage it at 30
mph), so would need to use a lower gear, thus resulting in higher engine
revs, and more noise in addition to higher fuel consumption.

Quoted message said:

I'm going to suggest congestion charge cameras which make
sure people obey the 20mph limits by averaging their time within the
park.

So they can drive around like nutters, endangering all-comers, so long
as they stop for a long enough "break", before exiting, to bring down
their average.

Quoted message said:

Also, for anyone who uses it solely to 'cut-through' a £5
toll

Would you expect pedestrians and cyclists to pay that too, for not stopping?

[1] <http://www.slower-speeds.org.uk/content/view/53/38/>

--
Matt B

elyob said:

Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

If you can find relevant figures for an average car I suspect you'll
find they do better at 30mph than 20mph so yes though these figures
are of course for a constant (unrealistic) speed. The reason is that
at low speeds the engine uses barely more than it does idling.

Of course for 20mph, unless you need the car you should be using pedal
power.

Jon

"elyob" <[email hidden]> wrote in message
news:[email hidden]...
Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

Just anecdotal, but some years ago I drove across Mali in an old Landrover.
We were on dirt roads/no roads and took a week to cover a couple of hundred
miles mostly in low ratio. Very worried about running out of fuel but
turned out that consumption was almost identical to if we'd cruised the same
distance in top gear.

Jonathan Schneider said:

If you can find relevant figures for an average car I suspect you'll
find they do better at 30mph than 20mph so yes though these figures are
of course for a constant (unrealistic) speed. The reason is that at low
speeds the engine uses barely more than it does idling.

A graph showing the general trend here:
http://www.fueleconomy.gov/feg/driveHabits.shtml

--
Tony

" I would never die for my beliefs because I might be wrong."
Bertrand Russell

PhilD said:

elyob said:

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

That sounds like something I used to hear a lot (not so much now) that
generally, driving faster = less fuel used = less pollution (and
conversly, ... slower = more... = more...). The main argument seems
to be being able to drive in a higher gear.

When I was at school I was told that the most efficient
speed for cars was about 56mph. (Obviously cruising, not
continually speeding up and slowing down). I don't know
where they got this figure from, or why they seemed to
think that is was the same for all cars.
This was also the speed that some car makers used for
their mpg figures. (makes sense).

On Tue, 21 Aug 2007 06:09:01 -0700, elyob <[email hidden]>

Quoted message said:

Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

He believes that the RPA is trying to close the park to all cars and
that the park is the main route for vehicles travelling between
Kingston and west London.[1]

He wants the RPA team retired and new 21st Century thinking people
brought in. I'm going to suggest congestion charge cameras which make
sure people obey the 20mph limits by averaging their time within the
park. Also, for anyone who uses it solely to 'cut-through' a £5
toll ... is that 21st Century enough?

In your reply you could mention that on 26th June a 53 year old man
was killed by a motorist in Greenwich Park as the cyclist rode slowly
up the steep hill. The speed limit in Greenwich Park is 30mph. Had
the driver been going at 20mph instead of 30mph there is a good chance
the cyclists would have survived, or the crash avoided.

www.greenwichcyclists.org.uk/News/greenwichpark.html

The white bicycle in the photo is still there, marking the needless
death.

Parks are there for recreational use, not as a motorists thoroughfare.

Tom Crispin said:

Parks are there for recreational use, not as a motorists thoroughfare.

Explain why you think (if indeed you do think) that pedestrians and
cyclists can use the park recreationally as a thoroughfare, but
motorists can't.

--
Matt B

Martin Dann said the following on 21/08/2007 16:23:

Quoted message said:

When I was at school I was told that the most efficient speed for cars
was about 56mph. (Obviously cruising, not continually speeding up and
slowing down). I don't know where they got this figure from, or why they
seemed to think that is was the same for all cars.
This was also the speed that some car makers used for their mpg figures.
(makes sense).

I know my car (1.8 Mondeo) will trickle along on cruise control at 50mph
in 5th recording about 50mpg so there's probably something in that. Go
up to 70, and the figure drops to about 35-36mpg.

--
Paul Boyd
http://www.paul-boyd.co.uk/

elyob said:

Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

Bit difficult to say to be honest, it depends on the engine, its
torque range, the gear chosen etc. At 30 my car is more fuel efficient
than at 20 in the same gear, plus people tend to put the car in a
high gear and strain the engine when going slow to get it to
accelerate. But a non-turbo car might be more efficient, mine having a
low compression engine means that off-boost im running in a low
efficiency range. Also I suppose you have to think that if you have /
changes/ in speed limit that means accelerating and decelerating,
which "wastes" fuel, whereas a straight 30 all throughout wouldnt
require it. I do have this argument with speed humps too though, they
slow everyone down so much that they race between humps to make up the
time, using more fuel and being more dangerous.

POHB said:

"elyob" <[email hidden]> wrote in message

news:[email hidden]...
Hi,

Just about to respond to a letter in my local rag r.e. Richmond Park.
The writer claims that driving at 20mph creates more pollution, he
doesn't back it up and wondered if there is any evidence to the
contrary?

Just anecdotal, but some years ago I drove across Mali in an old Landrover.
We were on dirt roads/no roads and took a week to cover a couple of hundred
miles mostly in low ratio. Very worried about running out of fuel but
turned out that consumption was almost identical to if we'd cruised the same
distance in top gear.

Thats because landies would struggle to be any less economical 🙂 But
in all seriousness in a low-range you're running the engine so
unloaded its barely trying.

On Tue, 21 Aug 2007 09:00:47 -0500 someone who may be Tony Raven
<[email hidden]> wrote this:-

Quoted message said:

Quoted message said:

He wants the RPA team retired and new 21st Century thinking people
brought in. I'm going to suggest congestion charge cameras which make
sure people obey the 20mph limits by averaging their time within the
park.

Don't you mean average speed cameras as fitted to many motorway road
works these days?

There is a minor road fitted with them near where I live.

The original plan was to close the road to motor vehicles, but there
was a row with people whining about how this was a bad idea despite
there being a new dual carriageway within 500m. The old idea of
eliminating the hills didn't appeal. So instead they fitted average
speed cameras. No-doubt the nuts who want to drive to work at high
speed are not pleased.

--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Clive George said:

"Tony Raven" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Sounds like that old one of being low on fuel and having to drive fast to
get to the petrol station before it ran out ;-)

I know people who have done that - one who was a reasonably respected
physics professor who knew it wouldn't help, but he did it anyway :-)

I once drove fast to get to a garage to save fuel. It was leaking out
of the tank so the faster I drove, the better.... :-\
--
Phil Cook looking north over the park to the "Westminster Gasworks"

On Tue, 21 Aug 2007 16:38:13 +0100, Matt B

matt.bourke'@nospam.london.com said:

Tom Crispin said:

Parks are there for recreational use, not as a motorists thoroughfare.

Explain why you think (if indeed you do think) that pedestrians and
cyclists can use the park recreationally as a thoroughfare, but
motorists can't.

It's the same reason that I do not allow horses to walk through my
living room to get to the back garden, but people, cats, and dogs are
welcome.

On Tue, 21 Aug 2007 16:38:13 +0100, Matt B

matt.bourke'@nospam.london.com said:

Tom Crispin said:

Parks are there for recreational use, not as a motorists thoroughfare.

Explain why you think (if indeed you do think) that pedestrians and
cyclists can use the park recreationally as a thoroughfare, but
motorists can't.

How nice, a Strawman.

The Greenwich Cyclists' Campaign is to have the speed limit through
Greenwich Park lowered to 20 mph and overtaking prohibited. This
limit would apply equally to cyclists, as do all speed limits in the
Royal Parks, including park vehicle roads where the limit is 5mph.