80 mph speed limit for UK + 10% + 2 mph = 90mph

Apparently you use about 20% more fuel ie more tax.

Brings us more in line with most of EUs 130 kph speed limit.

Curves of UK road are designed for about 77 mph speeds.

Perhaps it should be linked to having at least 3 mm tread depth?

I'd assume lorries will still be limitd to 56mph and minibuses to 62mph.

So greater speed differences between the traffic. Not sure it's a good idea.

Although the system in some countires where it's based on weather conditions makes more sense than a blanket limit we have now.

How about a better idea....

Limit all cars vans and buses to 56mph (with a speed limiter as used on trucks) and ban them from lane 3, this will mean that there will be less road rage as you will have to travel at a set maximum speed, thus saving money as your car will be much more fuel efficient.

THEN adjust the speed limiters off all the trucks to 80mph, and increase there speed limit to 80mph they can travel faster and concequently trucks will be on the roads for up to 1/3rd less time, meaning less lorry congestion !

I'd assume lorries will still be limitd to 56mph and minibuses to 62mph.

So greater speed differences between the traffic. Not sure it's a good idea.

Considering a large chunk of the traffic already does 80mph+ the change isn't going to make much difference to the speed differences between cars and lorries. The speed differences between lorries and cars are generally not a problem as lorries are easy to spot and you make allowances for them (although it will be even more frustrating getting stuck behind a lorry when they are overtaking).

It will make the speed difference between someone driving at the speed limit and a doddery¹ person driving joining the carriageway at 20mph larger and increase the consequences. These kinds of accidents are going to happen no matter what the speed limit is and cannot be prevented until we ban people from motorways that are incapable of driving at a safe minimum speed or getting up to that speed in less than a mile.

¹ I use the term doddery here to mean anyone who drives like the stereotypical octogenarian peering over the steering wheel with their nose pressed up against the windscreen. I'm not discriminating against the old here - there are plenty of younger people who drive like this (although they generally don't peer over the steering wheel in the same manner).

Although the system in some countires where it's based on weather conditions makes more sense than a blanket limit we have now.

This would probably be a good idea but has the problem of how do you implement and enforce it? The motorway network already has variable speed limit signs that are legally binding and could be used for this. But they are almost universally ignored by motorists as people have lost faith in them (I have yet to see a single person or animal on the carriageway when the signs have been on, although I have seen people in the carriageway when the signs haven't been on).

You also have the problem of at what point does the limit kick in? Heavy rain? Rain of biblical proportions? Light drizzle? You can't have a subjective system as it varies from person to person and an objective system would have to be controlled by the variable speed limit signs (with obvious problems).

In summary; I'm for increasing the limit to 80mph and generally for variable speed limits based on the weather but I can't see that they would work in practice.

I've driven in "dry" (no descending precipitation) conditions when everyone had slowed to 60 or less voluntarily due to flying spray, and in rain when I needed windscreen wipers on fastest intermittant, but the road surface remained dry. So how does a lower speed limit in rain make sense?

Also, what's "magic" about a tread depth? (well other than on Continentals, where the compound changes at 3mm) In dry weather, the less tread you have, the more grip you have.

Separate point on variable limit signs - I once saw then "being used to protect an accident recovery" - Great except that we were asked to slow to 30mph 5 miles from the accident site, so speeds went back up after we'd passed 2 signs that had no obvious reason for the reduced limit.

what's "magic" about a tread depth?

I'd assume two factors, those being that resistance to aquaplaning is meant to be closely related to tread depth, and that non-aquaplaning wet grip is said to drop significantly when tread depth is below 3 mm.

My opinion? I try to drive to the grip I can feel, and only change my tyres when I'm legally obliged to do so. Against that I weigh things in my favour by choosing tyres that are meant to grip well in wet conditions, even when worn.

I'd assume two factors, those being that resistance to aquaplaning is meant to be closely related to tread depth

Yes, but aquaplaning doesn't happen on dry roads, which is what I specifically related the point about the OP's use of a "magic number" to.

, and that non-aquaplaning wet grip is said to drop significantly when tread depth is below 3 mm.

I'd never heard that one before, and don't see why that would happen anyway.

I've read it in the garage I go to. Think it was a Michelin article. Quick google found this

http://www.conti-online.com/generator/www/uk/en/continental/tyres_for_life/themes/tread-depth/what_the_experts_say_en.html

I noticed that toyo's drastically reduced wet grip under 3mm. Pirelli on the other hand just keep going

Also, what's "magic" about a tread depth? (well other than on Continentals, where the compound changes at 3mm)

I've read it in the garage I go to. Think it was a Michelin article. Quick google found this

http://www.conti-online.com/generator/www/uk/en/continental/tyres_for_life/themes/tread-depth/what_the_experts_say_en.html

I noticed that toyo's drastically reduced wet grip under 3mm. Pirelli on the other hand just keep going

Note the point in bold face wrt your reference.

I normally do change at about 3mm, but that has to do with when I start getting the fronts spining up under acceleration.

The legal depth of 1.6 is now too little. With modern wider tyres there is a much increased risk of aquaplaning and anybody who has run their tyres down to near the present legal limit will know that they simply don't drive as well once they pass about 3.0 mm of tread, the also become more noisy. It would be interesting to find out tyre manufacturer's own research as to the degradation in performance as the tread wears down, also how the tyre compound itself deteriorates with age.

About Continentals -Aqua planning at low speed in the wet under slight to moderate braking when going up a slight incline persuaded me to change my Continentals when they were on 2 - 2.5mm front and 4mm backs. Also, the increased level of road debri, "Layed-down rubber" on the surface and reduced cleaning makes adoption of higher tread minima desirable. I'm convinced that in some adverse wet conditions, where you get a heavy film of water on the road driven by near horizontal wind, the water on the road starts exhbiting laminar characteristics making aqua planing more likely.

The French system of "Bad weather" speed limits works well on motorways/expressways without realtime signage.

IMHO, some of the motorways that are routed through areas subject to frequent bad weather e.g. M62 Pennines should remain restricted to 70.

And what about travel at night or in poor visbility on motorways with increased speed limits ? In the absence of motorway lighting, more people are going to resort to Xenons (In order to get a sufficiently long field of view ahead), with consequent increased dazzle. Time to consider some form of background lighting at least - French have illuminated marker posts at intervals along the central reservation on newer expressways.That's probably OK for some of the lower intensity of use rural Expressways in France, but our motorways need something a little more. No reason why that couldn't be a continuous low intensity bead (Fibre optic ?) down the central reservation and along the nearside lane edge . People loose depth perception and a sense of direction in near total blackness/zero vis,a carriageway boundary marker might go some way to restore this -cats' eyes aren't always sufficient giving you only a fleeting view of the minimum braking distance in front. This would produce an effect similar to that seen in the time lapse photos of moving cars rear lights. Nighttime driving psycholgy might change - if you can see 1/2 mile ahead instaed of just 300 feet you can plan accordingly.

Bet TRL have loads of data on this.

On fuel consumption, travelling at 80 probably means a 5-7 MPG loss over 70 for my wagon.

Nick

Edited 12 May, 201115 yr by Clunkclick