Looks like they are considering putting a section of the M1 to 60, mainly for emissions
http://www.bbc.co.uk/news/uk-politics-25619914

Personally I think its madness, there needs to be a review of roads with a view to increase speed limits especially on Motorways and redesign of roads generally for safety (like that ill happen) Mike

2014 Facelift Discovery

And no doubt they will be installing average speed cameras with a view to increasing their revenue

The so called other advantages given, i.e. "reduced congestion, increased capacity and improved journey time reliability for users of the motorway". just show how these authorities believe that the general public has such a low IQ that they won't see through their silly schemes.

Emissions/pollution is a poor excuse, if they are so concerned about pollution in general why must we sit at idle for minutes at traffic lights on roundabouts in off peak hours when there's no traffic on the roundabout

I totally agree. There are plenty of other examples of good roads network and designs, like: the USA right turn on red, Germany autobahns, most European roads approach to incidents etc

Ive never seen the M25 or M42 add any real value (but then I wouldn't get me started on that or this new desire to put motorway road work schemes at 40mph for safety...it used to be 50mph now 40 soon it will be 30!)...just like when all the back roads get put to 50, they will then want them at 40 for safety - its happened loads around here.

I wouldn't get me on a rant!! Mike

2014 Facelift Discovery

Reducing speed does increase capacity (within limits of course). It will also reduce emissions quite obviously. It would seem likely that this temporary measure is the first stage of a general cut in speed limits (with associated tax raising, sorry I mean safety cameras).

I'd rather see them putting resources in to getting automated road trains in place. That's the automatic "follow the leader" systems that allow vehicles to tailgate at speed under computer control. That would massively improve capacity for a start. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

I would argue the emissions point, although only from the stance that its a relative cut eg: a car designed to do X emissions at 70 will do less by driving slower in theory because of less revs...equally put it in 5th from 8th, revs increase and emissions (overall )don't change...but most cars are now designed with emissions in mind anyway. A good friend also makes some valid arguments about emissions linked to fuel use, which again makes the point of speed and MOT type emissions test difficult to explain (he works in the automotive industry and as I cant explain as well as he, im not going to try)

The reducing speed to a regulated X, in theory, should give better regulated flow to allow better movement through a section - it doesn't increase capacity...the road is only a certain width and length (just like a water pipe). Personal experience (and I cant remove increases in use), its all in theory the roads with it don't feel any better...there are still accidents, so no safer. They probably build frustration and other unmeasured issues.

There is probably an argument about increasing speed to get better regulated flow, if there was some uniformity. But again not something I can comment on in any way!

Road trains...I still like driving, so not a bad idea - but not something I would like to use. That said your right - these are the sorts of development to improve transport not reduce it.

Equally - make rail better/cheaper so more people can use that as a viable option etc etc Mike

2014 Facelift Discovery

The chances of doing much more than 60 on that stretch is confined to the early hours.

As for road trains they aren't feasible. The technology is vastly too expensive for controlling a mixed population of vehicles types and ages with the problems of junction etc was all trotted out and studied in the '70s, '80s and '90s. Give it 50 years and it might start to be relevant.

The planning for road trains needs to start now if we are to be in a position to implement them in a reasonable time scale. For a start, the vehicles themselves need to have the facility built in. No reason why the sort of systems (active cruise with queue assist is effectively a stand alone part of a road train) seen in upper sector vehicles can't be made main stream over the next ten years. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Mike, if you reduce speed then you reduce fuel usage (within limits). If you reduce fuel usage then you reduce emissions (again, within limits).

Reducing speed does increase capacity because you can run the vehicles closer together. You get more vehicles per mile of road. There is a "sweet spot" for any given road where the capacity and throughput are at their most efficient and the maximum number of vehicles can be flowed along the road. It's not like a water pipe because water isn't compressible in the way that traffic is. It's a while since I read any of this stuff but it's surprising how slowly you can run a motorway and still get lots of traffic through in a good time.

As always, the problem comes when you get some idiot who thinks he's more important than everyone else and either tailgates someone in to an accident or causes a brake pulse behind him (because he's constantly on and off the brakes in his attempt to scare the person ahead out of the way so that he can gain one place along the queue). This sort of idiot is the one who causes the hold ups in the first place. Him and the idiots for whom the phone is more important than anything else in their lives. Distraction plus speed equals messy outcome.

I'm all for improvements in rail / other public transport. I'm currently making use of th park and ride system in Oxford. It's great - drive to the outskirts, £2 for a day's parking, £2.70 for the return bus trip. Drops off in the centre of the town and is regular (every 8 minutes during the main part of the day). Much happier doing that than sitting in traffic for 20 minutes burning fuel and going nowhere and then paying £15 for the day's parking.

Of course, we could always go cross country to our destinations - we do have excellent 4x4s...

Sadly, I fear that the eventual outcome is that increasing numbers of roads will be made in to toll roads like the M6 Toll. This will move some traffic on to minor roads creating local issues but the arterial roads will improve and the politicians will crow how successful they are at solving the traffic issues! I like the M6 Toll but I'm not sure I'd want to pay £50 in tolls to go a decent distance along the motorways. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Im sorry, maybe there is a miss understanding...but reducing speed, doesn't reduce fuel usage and thus reduce emissions - at least not as simply as its made out. Firstly I will point out that, I did say there could be a relative decrease in emissions, but that actually there were other factors. For example
1) acceleration is the actual the significant issue with emissions and fuel use
2) Cars designed to do 70mph in 8th @ 1500rpm might be in the engines sweet spot...drop it to 50, the car might now be in 6th @ 1650rpm at 50mph, therefore not using less fuel and not using less emissions.
3) There might also be a need to drop the gears to ensure you are labouring the engine or can make it up a hill etc etc etc...therefore you might drop from top gear to a lower gear. The engine might not be in the most efficient gear and therefore use more fuel - more emissions etc etc.
Anecdotally, Doing an average of 100 on the autobahns in Germany, my range rover returned some of its best MPG ever - therefore using less fuel and therefore polluting less. Considering I did a lot of UK motorways at 60ish, this tends to highlight its not that simple.
Car engine design has moved on from the old days when things were this simple.
...the list of examples does go on, but some of the principles require an ideal, sterile world - which fortunately we don't live in.

On Capacity and Speed - Correct me, you said speed increases capacity? Speed does not increase capacity - it increase flow, flow ensures the same capacity can move through the system faster, not more capacity - even if you get cars closer together...you aren't increasing capacity, your increasing flow or possibly the carrying capacity, the capacity hasn't changed, you have just improved your ability to get something through the system - which is why they run the hard shoulder now to allow more capacity.

Think about a water pipe a little more - your correct about not compressing water in it (although maybe a water pipe was a bad analogy)...but you cant compress a car either, you can suggest decreasing the gap between cars, in theory...but that has nothing to do with speed (I might leave the same gap at 50 as 150 for example). Regardless a pipe (be it water or gas) still has a maximum capacity, look at rivers flooding when they hit a bridge and the water is forced through the opening - the bridge has a daming effect and water backs up the bridge cant handle any more capacity. Its a bit like data - but my ict days are long behind me, you can make more effective use of the capacity you have...but you still have 3 lanes to get it through.
Every day, despite doing 50 or 60mph on the M42, I don't get through it faster...in fact I get through it slower. What the HA say that ive talked to (and I know some of them) is not about getting more through...its the consistency and therefore reducing the queuing congestion etc - you still get the same number of cars through, it just takes longer...but doesn't halt all together everyone.

That said - again this is idea world stuff, because within that, you touched on it, not everyone goes at a uniform or consistent speed (loads of factors from not caring to speedo differences or vehicle limits), people need to move lane and many many other system issues eg. people not paying attention. All that means the net gain is marginal if there was any to begin with...other than everyone arriving in a place a little later than they would have.

Personally, I would much rather drive to my destination - plan my journey, come and go when I want in my own comfort etc etc than wait and often parking is cheaper than the whole public transport cost (but then that's a different story) Mike

2014 Facelift Discovery

Some cars might be geared to give max economy at 70mph but I bet many aren't. The EU fuel consumption test has a max speed of 75mph but averages at about 40mph in the extra urban test. So getting good economy at speeds lower than 70mph is likely to give better EU fuel figures - and that is important for the manufacturers.

Acceleration is a big fuel user (especially as mass increases but the relationship is linear) but so is drag - power absorbed by drag increases with the cube of speed. If you want to drive at a higher speed you need more power (there is an issue with gearing etc, too of course). More power uses more fuel. I'm amazed that your vehicle gave its best economy at 100mph. I think that is what is known as an "outlier".

As for speed increasing road capacity, no, I'm saying that there is a best speed, a sweet spot, where throughput is at its highest. Traffic is compressible - it tends to run closer together as speed reduces and vice versa. Most people will not feel as comfortable 10m from another vehicle at 70mph when they would do at 30mph for example. Thus as speed increases, traffic density will tend to reduce. The individual vehicles get through the mile quicker but the overall number of vehicles through the mile in a given time period reduces. The sweet spot exists where the distance between cars in a lane (density) and the speed of the cars in the lane combine to get the most vehicles along the road in a given time period. Adding another lane gives more overall capacity but it is very expensive - varying the speed to run the road at its maximum throughout at peak times is much cheaper to do, although possibly less popular with some motorists.

In order to maintain safety at reasonable levels, gaps between vehicles need to increase with speed because drivers get distracted and they have a measurable finite reaction rate. An automated system can allow much closer running because it can measure distances precisely and at a very high rate continuously - it doesn't suffer from the distractions that drivers suffer from. In lieu of automated systems, speed is reduced to improve throughput.

I'm in the camp that would favour the introduction of undertaking (overtaking on the left) on motorways. Then we wouldn't have the silly situations where the right lane is nose to tail behind some donkey whilst the centre lane is relatively free. This is particularly a problem on dual carriageways. If people aren't comfortable with being undertaken then they can stay off the motorways.

And as for parking being cheaper than public transport - it doesn't appear to be the case in Oxford. Parking is expensive and public transport isn't. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Had anyone done a real time fuel economy test in the sport?

Mpg at 60mph
Mpg at 70mph
Mpg at 80mph

Monitored over the same journey at the same time of day.

There must be a sweet spot like it had been suggested and i assume if different for each car.

I remember someone posting they got better mpg at 80 mph then 70mph.

One other problem with this totally irrational scheme that nobody not even the media have highlighted is that all car speedometers are deliberately designed to over-read; many by as much as 15%. This means that lots of muppets will be driving at 51mph thinking they are doing 60.

The RRS is not immune to this self deception. When my speedo is reading 80 the iPhone GPS reveals the actual SOG to be only 70 mph an error of about 13%. 2008 MY Java Black TDV8 HSE

There is an error - but I wouldn't rely on that too much, the error on a new sport is only a few MPH, older sports might be more for sure. GPS isn't perfectly accurate either...but your point is also correct Mike

2014 Facelift Discovery

At 30 mph showing on my dash, my road angel is showing 27 mph. At 70 mph on dash my road angel is showing 66 mph. My road angel is the correct speed and the one that i go by at all times. Its surprising how may cars i follow in a 30 mph zone and the car in front is only doing 26-27 mph. (20" wheels by the way) On 22's the cars speedo was a little more accurate with the road angel. This polution argument is a load of , no matter how many lanes there are, there will be still the same number of vehicles passing through, its just that they will all be going through 10 mph slower causing congestion further back down the motorway at peak times as the faster traffic catches up with the traffic doing 60. Its always the same when traffic is forced to slow down increasing the chances of a collision.

Quote:

Its surprising how may cars i follow in a 30 mph zone and the car in front is only doing 26-27 mph.

Glad to hear it. 30mph zones tend to be places where the locals actively try to kill themselves under your wheels. Driving a bit slower might just foil their suicidal plans and protect your paintwork.

If you follow me through a 30mph limit you'll generally find me travelling at less than 30mph too.

On national limit roads, you'll usually need to be going a bit more than 60mph to stay with me...  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed