JNugent wrote:

Velvet wrote:


JNugent wrote:


Ambrose Nankivell wrote:


[ ... ]


... If you want to discredit speed
limits, then give examples of where they're set too low or too high,
rather than criticising signing policy.


How about 40mph on the M4?
And no, I am not referring temporary limit at a set of roadworks
(even though 40 is still extracting the urine a bit, even at
roadworks). I am speaking of a permanent limit of 40mph on part of
the M4.
Do you not agree that such a limit is *way too low* on a motorway?


And exactly where is this 40mph on the M4? Perhaps where it passes
through a built up area in London, where the lanes are narrow and it
twists with frequent junctions?


I don't know what you are trying to imply, but a motorway passing through a
"built-up area" is entirely separate from the local road network. Think of
the M6/M5 in NW Birmingham, Dudley, Walsall, etc. Perhaps you think they
should be limited to 40 as well?

That depends on the local circumstances. Having also driven that
several times, I would say it is possible that it should. It can get
very busy, and have long queues in one (or more, but often one) lane as
people attempt to join/exit the motorway, with faster traffic in the
other two. I have seen nasty near misses where people attempt to queue
jump, and try and join the faster moving lanes from the queueing one,
then cut back in later on.



The Chiswick Flyover's lanes are exactly the same width as any other
motorway lanes (12' wide). It doesn't have hard shoulders, but then, neither
do a great many 2 x 2-lane d/cs limited to 70mph - so of what relevance
could that be?

Possibly the fact that it is:

a flyover. Some vehicles can end up over/through bridges and on the
road below that they span - or has this not occurred to you? I've
actually seen that happen.

no hard shoulders - on a road as busy as that, it is inevitable that
breakdowns and accidents occurr. As such, there is no way to get cars
out of the main lanes, and the impact on traffic is severe, causing
queueing, and approaching such a situation at 70 can be very dangerous,
approaching at 40 takes away some of that danger though not all.

queueing - I've seen this many many times on this stretch. Approaching
a queue at 40 is a wholly different situation to approaching a queue at
70-80, as would happen if the limit was as you appear to want it, 70.

multiple bends leading to restricted visibility - again, a valid reason
for the limit to be lowered.

short slip lanes onto and off - as you drive this, no doubt you're aware
of the short length that the slip roads parallel the main carriageways,
no? The faster the speed of the traffic on the main carriageways, the
longer the slip lane must be to avoid the problems where vehicles are
unable to merge successfully. This is, as I'm sure you're aware,
exacerbated by the fact that there are no hard shoulders in which to
utilise in this situation - you're faced with making a dead stop before
the concrete barrier gets you, or swerving out into the side/right in
front of someone at the last minute.

And as a regular driver, I'm well aware that since the limit was
lowered, there are less accidents on that stretch, and journey times are
more predictable.

Exactly which ones of the above reasons are you going to disagree with,
I wonder.


As for "frequent junctions"... there is one junction (where the A4
"becomes" the M4) at the western end and one intermediate junction (with the
N & S CRs).

Let's see... that's... er... two junctions.

You'd have to be pretty weird to class that as "frequent", wouldn't you?


Perhaps I'm thinking of further on, where it becomes the A4, but
regardless, the traffic flows better since the limit was set to 40.
Live with it.


I drive the M4 regularly, between central london right out to Wales.
The only place I can think that such a limit exists is where you get
close to London, and there are very good reasons for the limit at that
point.


In that case, you'll have no difficulty in explaining them.


Already done.

Some more information on where your 40 mph limit on the M4 would be
useful in determining whether it is justified and thus not a valid
piece of supporting evidence; or not.


Are you denying that there is a permanent 40mph limit on part of the M4?


No, please read more carefully.


A funny thing to do for someone who claims to drive on it regularly.

Indeed, but as I said, you should read more carefully, I didn't deny it,
I merely asked you to state where it was, so we could be sure we were
both talking about the same thing. To the casual reader of *your* post,
you seem to be talking about a stretch of the M4 that is 3 lanes wide
with full hard shoulders, that has the same with a 70 limit to each side
of it, admittedly this would be a little peculiar.

By omitting to state where the limit was, or give any other information
on how the road differed from the more common motorway, you appeared to
be attemping to mislead by omission.

Since you chose to use the 40 mph limit on the M4, yet omitted to state
*where* it was along the length, it was incumbent upon you to clearly
define where it is, not me.

Obviously the subtly of my post sailed completely over your head.


--


Velvet