Speed Limits, Road Safety, Technological Change, Economic Growth

ILW

J_i_m wrote: »

That is a little bit simplistic. A difference in speed one way or the other doesn't directly affect your fuel consumption.

What gear your're in plays a very large part, for instance doing 30mph in 5th gear (so long as your car will do that) uses less revs and hence less fuel than doing 30mph in 4th gear. In fact being forced by the other traffic to drive very slighty slower may mean you have to change to a lower gear to prevent your engine from stalling and this would actually use more revs and use up more fuel.

So driving faster doesn't automatically mean using more fuel, often it helps the car to use it's fuel more efficiently.

Infect if your're in town traffic and there's stop start traffic then despite driving slower you're actually using up more fuel because to get the vehicle moving from standstill or crawling speed requires more revs.

But having said that, probably in most cars driving at 80mph would use more than 70mphm since you'd already be in top gear.

I belive the coefficient of drag (Air resistance) is not linear. eg double the speed quadruple the drag.

Having said that I do drive a little convertable at the weekend which with the hood down has the aerodynaics of a open umbrella.

Pennywise

Slowing down traffic when there is no real need will cause more accidents - not just to frustration and silly people trying silly things to overtake or take short cuts, etc., but by causing less opportunities for other drivers to join the road from side roads or for cycles, horses and pedestrians to cross.

We had a 40 mph road through our village and there were plenty of "gaps" between traffic to let you cross or join the road. They changed it down to 30 and now it's a constant stream of traffic, nose to tail, that's virtually impossible to cross/join meaning loads of minor shunts when people get frustrated at waiting and take risks, or tailgating to stop people crossing/joining.

Now the lunatics are proposing reducing it to 20 because there's a school nearby and because of the number of minor shunts (caused by the lowering in the first place!).

Same on the motorway, the HGV limit just causes lanes 1 and 2 to be almost permanently blocked, meaning two relatively lowly used lanes and everyone jostling for places in the third lane to pass them. If we need low speeds for safety, then why not have speed limits for each lane, i.e. 60 for the left lane, maybe 70 for the middle lane and then 80 for the third lane, with lorries limits being raised slightly as well.

Increasing the motorway limit to 80 without tackling the problems of the restricted HGVs won't help - it will make things worse and more dangerous.

Kennyboy66

Thrugelmir wrote: »

Amazes me the speed car drivers go in fog.

People drive faster in fog, the longer they have been in it.
Often they cannot perceive how fast they are going because of the lack of reference points and because fog scatters light.

chewmylegoff

J_i_m wrote: »

What gear your're in plays a very large part, for instance doing 30mph in 5th gear (so long as your car will do that) uses less revs and hence less fuel than doing 30mph in 4th gear.

just because the revs are lower, doesn't mean that less fuel is being used. if you are in an inappropriately high gear, you can be using far more fuel in each cylinder ignition than if doing more revs in a lower gear, such that more fuel in total is being used in the higher gear. if i crawl along at 30mph in 6th in my car, my car's computer tells me i'm doing far fewer mpg than if i drive it in 4th at the same speed.

Sir_Humphrey

One problem for Hammond in changing the speed limit is that any pile-up caused by high speed can now be pinned on him by his enemies. It wouldn't necessarily be fair, but that's showbiz.

I am not convinced of the political astuteness of this, but then again that part isn't my job!

pqrdef

Thrugelmir wrote: »

Amazes me the speed car drivers go in fog.

How slow should people go? If you go by the distance you can see, you're going to crawl. I do this on country lanes, and find myself pursued by an impatient queue, who of course have the advantage of having my lights to follow.

but on a motorway you can often tell from lights ahead that traffic is flowing smoothly for some distance ahead, and that's about all you need. It's all you've got at night anyway, because headlights aren't much use at motorway speeds.

sharnad

The_White_Horse wrote: »

speed limits on the motorway should be abolished.

most speed limits should be abolished. they are nonsense. driving at 20mph at 3am beacause you are near a school is madness.

the police should just police "dangerous" driving. we need to get through people's heads that speed does not necessarily mean dangerous. sometimes it does, but not always.

You really need to look at how much speeding kills, safe stopping distances and how many more people would die if people could just do whatever they want

TruckerT

Kennyboy66 wrote: »

People drive faster in fog, the longer they have been in it.
Often they cannot perceive how fast they are going because of the lack of reference points and because fog scatters light.

That is a reason, but it is not an excuse!

About 15 years ago, I started the Institute of Advanced Motorists course, and was allocated a trainer. Early on an autumn Sunday morning, in fog as thick as I have experienced in my lifetime, my trainer announced that we were to go on to the motorway. I questioned the wisdom of venturing into such a dangerous environment on a totally non-essential exercise. He reluctantly changed his plan, and we turned onto a dual carriageway instead. For a couple of miles the trainer was nagging me to go faster. At the exit from the first roundabout, the road became a single carriageway, and the trainer continued to criticise my slow speed. As we started to enter the single carriageway, we were suddenly head to head with another car which was completely on the wrong side of the road, but we both stopped with a few inches between us

TruckerT

TruckerT

mattcanary wrote: »

Tescos lorries do seem to be the ones that never go above 40 mph on single carriageways. Other supermarket's lorries do seem to go rather quicker

Unlike most haulage companies, the big supermarket chains have the financial freedom to schedule enormous amounts of slack into their journey times. They are also at pains to maintain a squeaky-clean and 100% law-abiding public image

Their vehicles are satellite-tracked, and driver behaviour is closely monitored. The fact that the 40mph single-carriageway limit actually creates danger, by generating masses of road rage, and frequent potentially-lethal overtakes, is no concern of Tesco

TruckerT

TruckerT

lisyloo wrote: »

At 1.8 million a pop, how many fatalities do you think you'd need to save?

Modern trucks (and maybe also cars), have a fly-by-wire throttle control - ie electronic not cable-operated. Modern trucks have a variable speed limiter which the driver can swutch on or off and vary at will, to suit changing speed limits. In an emergency, the setting is cancelled in an instant by flooring the gas pedal

It would surely be possible for an overhead signal to be sent to a receiver in the vehicle, which would automatically set the vehicle's speed limiter to any change in speed limit

TruckerT