Nobody likes a concrete road. England has 172 miles of concrete trunk roads, and promises have been made time and again to get rid of them all. But perhaps there's another solution.
You know a concrete motorway when you drive on one. The whining, droning noise from the tyres. The loud rhythmic thumps and jolts as you pass over the expansion joints. It's so unpleasant that the AA report some motorists thinking there must be something wrong with their car. Perhaps the only good thing is that heavenly feeling as you pass over the last jarring expansion joint, crossing onto black tarmac again, and peace and quiet returns.
It's been a while since we built concrete motorways. For many years, it was routine to invite two types of tender for construction of a new road - one for flexible (tarmac) surfaces and one for concrete - and see which was cheapest to build and maintain. But in the last twenty years concrete has been so unpopular that it's not even a contender any more, and since the late 1990s there have been periodic promises to get rid of all the concrete surfaces remaining on the trunk road network.
It's starting to look like there's another way that won't involve replacing the concrete at all. But before we look at that, we should probably ask why concrete roads were built in the first place.
In the late 1930s, believing themselves to be on the brink of a huge (and lucrative) roadbuilding boom, the Cement and Concrete Association published a book called "Construction of Concrete Roads" that set out modern construction methods and gave their product the hard sell. They set out the reasons why concrete was then (and still is) a good material for road construction.
"The advantages of concrete - low initial cost, low maintenance charges, durability, safe surface for motorists, etc. - have proved to apply equally to heavily trafficked highways as well as to the carriage-ways on housing estates."
By the time motorways came along the plain facts hadn't changed. Where the tender price was lower than the cost of building and maintaining a tarmac road, the Ministry of Transport (and its successors) were happy to see a concrete road built. It often cost a bit more, but in the longer term a saving would be made on maintenance.
A motorway with a flexible surface, for example, might need patching or resurfacing of heavily worn areas after about a decade: lane 1, which is heavily used by HGVs, will be resurfaced relatively often. A full new surface might be required after twenty years, and 30-40 years down the line the whole surface might need to be stripped off and several sub-layers might have to be rebuilt.
A motorway with a concrete surface? Find yourself a hobby. It'll carry on for decades.
The fact that concrete is low-maintenance explains why it's popular in countries with vast road infrastructure but little government money for upkeep. The USA is the obvious example. Oddly, though, while concrete freeways are rife in the USA, they don't have the dreadful reputation they have here. We'll come back to that.
Falling out of love
Concrete roads have three key properties that mean they are unlike flexible pavement surfaces, and which cause all the things that people don't like.
Concrete is (usually) laid in sections.
If you pour a continuous line of concrete to make your road, it will crack, which is bad. Concrete cracks because it's rigid and doesn't cope well with the expansion and contraction it experiences through changing weather conditions. So, to prevent cracks, it's laid in small segments, which butt up against each other at expansion joints, giving the slabs room to expand without cracking. All of which is fine, until you drive over them at speed and the joints start rhythmically thumping under your wheels. The older and less well maintained the expansion joint, the noisier it is.
Concrete is ridged.
If you roll out a tarmac surface, you roll it flat. But a concrete surface that's perfectly flat is perfectly smooth, and nobody wants a glass-like road surface. It has no grip. So, after laying a concrete road, ridges and grooves are formed across its width. They're randomly spaced and at random depths, to prevent passing tyres creating a continuous whine of the same pitch, but that's little consolation: passing tyres will still create a continuous noise as they pass over the ridges, like a stick being dragged along iron railings.
Concrete is non-porous.
Unlike tarmac, which has lots of holes and a natural roughness to its surface, concrete sets solid and has very few natural fissures and crevices. On a tarmac road those air gaps absorb some of the noise from passing tyres, and tarmac doesn't make much noise anyway. But concrete does, thanks to those ridges - so the sound of tyres can be deafening. As concrete ages, it's polished by passing traffic and becomes smoother, generating even more noise.
Most of the trouble is, really, about noise. Towards the end of the era in which concrete was still used for new roads in the UK, manufacturers came up with something called "whisper concrete" to address it. The Highways Agency announced in 1996 that it would be mandatory on new concrete roads carrying more than 75,000 vehicles per day, and trials were successfully carried out where whisper concrete was laid on the M18 in Yorkshire and the A50 in Derbyshire.
Whisper concrete was a last gasp for concrete roads. People didn't like them and their minds were already made up. Time and again, the public expressed a preference for tarmac.
Papering over the cracks
Since the late 1990s, there have been repeated pledges to get rid of concrete on our road network - popular announcements, but not necessarily followed up with energetic action. The latest was in December 2017 from Highways England.
The proposal has been the same every time: lay a thin course of tarmac over the concrete. That gets rid of the surface noise and the expansion joint noise at the same time, which is fine, except that it's a time-limited solution.
Tarmac will, naturally, need renewal much sooner than concrete, so laying it over a concrete road introduces a new maintenance overhead for ever more. It also won't stick quite as well as it would on a road bed designed for tarmac, and after a few years will begin to break up around the expansion joints, requiring patching or resurfacing even sooner.
Nonetheless, this solution has been used many times, sometimes even on brand new roads. In 1999, a new length of M1 opened around the east side of Leeds, one of the very last concrete motorways to be built. Within weeks of opening local residents in the towns and villages it passed were complaining about the unbelievable levels of traffic noise from the new motorway - all the more incredible because, in its early days, it really wasn't all that busy.
The solution was to lay low-noise tarmac on sections of the brand-new concrete that were within a certain distance of residential areas. Today, if you drive the M1 between junctions 43 and 47, you'll pass back and forth between tarmac and concrete over and over again. And today, of course, you can start to see it deteriorating, with long thin patches covering places the tarmac has already broken up over the expansion joints.
Experience with over-laying concrete has clearly proven it's not a good way to get rid of concrete road noise. It's time to look at a different solution that doesn't involve replacing concrete at all.
Diamonds are forever
If you drive some of those concrete freeways in the USA, you might be surprised at how different they are to a concrete motorway. They don't make nearly as much noise. There is a reason for that.
Unlike in the UK, where a concrete surface is left alone and deteriorates slowly over decades, increasing in the surface noise it generates, concrete roads in many American states are treated periodically with a process called diamond grinding.
It means exactly what it says - a machine with diamond-tipped blades grinds the surface of the concrete, cutting new ridges - this time in line with the direction of travel, not across it. That has the effect of re-levelling the surface and making it less coarse. The grinder can also level out any bumps or differences in level between adjacent slabs, if any have formed. A concrete surface can be re-ground like this several times, perhaps decades apart, before it needs replacement.
The result is that your long-lasting concrete surface can remain, rather than being overlaid with something shorter-lived, maintained in a state that makes it smooth and quiet to drive.
Back in 2009, the Highways Agency decided to give it a go. In a trial overseen by the Transport Research Laboratory, several short sections of road were subjected to diamond grinding, and then tested long-term for the effect on noise, grip and durability.
The first to be done was a section of the A12 Chelmsford Bypass, near to Boreham, and a further experiment was made on the A14 near Ipswich. The results were good - as they should be, for a technique already routinely used for decades in the US - and the cost was said to be half that of overlaying the same length of road with tarmac. More impressively, skid resistance improved by 54%, while road noise reduced dramatically and noticeably.
Things have gone a bit quiet since then, but if you've driven in to London on the M1 you might have noticed something quietly happening near Watford. A particularly noisy concrete surface on the southbound side between junctions 5 and 6 became, in 2018, a bit less noisy. The only hint at what happened is a blue sign that reads "M1 J6-5 Bricket Wood to Watford Concrete Surfacing Treatment Trials Sept 2018-2022".
It's fairly clear - if you have the chance to glance down at the surface - that the horizontal ridges have been replaced with smaller longitudinal grooves, and the cats' eyes have been pulled out and replaced with stick-on road studs, meaning a diamond grinding machine has paid a visit to Hertfordshire. It's also clearly a long-term trial, the outcome of which might not be known for another three years.
What's interesting is that, since this trial started, Highways England has not just gone quiet about resurfacing concrete motorways - it's actually started kicking resurfacing projects into the long grass. One example is the M27 between junctions 5 and 7, now undergoing a Smart Motorway upgrade, where Highways England announced earlier this year that the road would not be resurfaced:
Our recent surveys have revealed that the concrete here is still fit for purpose… However, Highways England recognise there are some benefits to resurfacing the concrete section with a low noise surface and we commit to doing this after we have completed the smart motorway works. We are working to find the best way to deliver this.
"Working to find the best way to deliver this" suggests that rolling a thin layer of tarmac over the top might not be the only game in town.
Another potential candidate is the M25's southwestern section, which has the most appallingly noisy and bumpy surface. Resurfacing is off the cards, because the motorway there is maintained for Highways England by a third-party company whose contract doesn't cover the higher maintenance burden of a tarmac overlay. Diamond grinding might be an economical way to fix the surface, and would leave the hard-wearing concrete intact. We will see.
2022 is a long time to wait for results. Perhaps the benefits will be recognised and the trial wrapped up sooner than that. Whether or not that happens, it is starting to look like Highways England might not be getting rid of concrete roads at all; it might instead be doing something much more sensible, which is taking the concrete roads it has and making them pleasant to drive on.
They may, one day, turn around the reputation of concrete roads in the UK. They might even start building concrete roads again.
I used to drive to and from university over that hideous southwestern section of the M25; absolutely dreadful surface. The vibrations go right through your body and just make driving that way really unpleasant.
Where the "experts" got the name "whisper concrete" from, one has to wonder. Maybe they were all deaf !! I use the A50 quite frequently and the noise into the car of this concrete surface has to be heard to be believed. The villagers in Doveridge complained long and bitterly about the noise, so HE (or HA as it was), gave them a lolipop to shut them up in the form of slip roads so they could get onto and off the A50 on the western side of the overbridge, none having been provided previously. This seemed to silence the protest !!
I actually moved to Doveridge two days after Fraser’s comment, living about 300m from the A50. The noise problem is worst when the wind direction is from the east and it is the one thing that spoils what is otherwise a lovely village. I live in hope that one day something will be done to improve it, whether tarmac overlay or diamond grinding, as the council should have never approved new developments in the village without addressing the road noise issue.
Great article, now I know why US freeways seem to be so quiet compared to our deafening concrete motorways. But something really needs to be done with the SW section of the M25, I feel like that over the years parts of it have been tarmaced over, but those horizontal ridges from its widening quite often catch my tyres.
Here in Hong Kong tarmac dominates the roads. Maybe if this technology is available here things will start to change, but I understand the current relationship between the US and China makes this more difficult to happen.
The SW sections of the M25 look to have been diamond (or just Freddie Flintstone large rock) grooved. These grooves are I believe the cause of much of the problem. They make a terrible din and catch your tyres and affect the steering. It is by far the worst part of the motorway network in the UK .
If the grooves make a lot of noise and are big enough to alter the direction of your car, they are not the result of diamond grinding! The south western part of the M25 hasn't been treated this way; what you're experiencing is the texture of the road surface as it was laid, subject to 30+ years of deterioration; the early 1990s widening that resulted in the concrete slab sections no longer lining up with the marked traffic lanes; and the slabs themselves gradually settling and coming out of vertical alignment with each other.
I used to drive for many hours a week over concrete roads; A50, M54, M5, M6 (short stretch near Junc 12) etc and I don't recall being bothered by noise or vibration. Maybe it is less annoying in a larger vehicle than a car. (Of course the people living nearby probably didn't share my indifference). I did often think that at least the first lane should be concrete though as the grooves caused by hgv's can become like railtracks. You could literally take your hand off the steering wheel and be kept on course for miles. Not that I tried this of course...
Slghtly digressing from Motorways; I definitely think there IS a place for concrete surfaces. Wherever traffic turns in a small, tight area, tarmac (or to give it its proper name 'Asphalt Cement), gets churned up in 'waves' pretty soon after being laid. That's why distribution centres that have hgv's constantly turning are done in concrete. Having, over the last few years, noticed that newly laid tarmac doesn't seem to last very long these days (certainly in the town where I live), I think that T junctions where lots of vehicles are turning, stopping and starting certainly should be concrete. Back to Motorways though- the ends of slip-roads would also be better done this way. I've noticed in Los Angeles (where the Freeway is Asphalt), the last part of the off-ramp is often concrete. As well as providing a far longer lasting surface, the change in colour (black to light grey) serves as an extra 'warning' to slowing traffic. I know they don't have roundabout junctions, but I don't see why our roundabouts themselves couldn't be surfaced in concrete. The traffic is slow moving so noise shouldn't be too much of a problem and the years without major re-surfacing works causing congestion would certainly be a blessing to drivers.
Pretty much right, but the other aspect is the wholesale abandonment of Hot Rolled Asphalt in the 80s/90s by government diktat that has caused the problem. The newer materials just cannot cut it. Many councils are going back to HRA, although it is noisier. Also the use of very thin top surfaces using SMA to resurface is just asking for trouble. A busy T-junction near me is already breaking up after relaying about 5 years ago, yet HRA-laid junctions continue to stand up even after 30 years.
Don't also forget the huge roll-out of three axle trailers. The scrubbing action of these is just ridiculous, and one wonders why government allowed them to be used as built.
Yes, that's true. Mind you, 5 years is a long time compared to the terrible standards I've seen over the last few years in Shropshire!
I was talking to a road guy a few years ago while they were asphalting and I mentioned how the lines painted on the roads don't seem to last five minutes anymore. He agreed and said they'd changed the formulae a few years previously and made it more brittle - not only making it more dificult to lay, but it also then doesn't have the flexibility to move, hence starting to crack and fade after only a few months so they have to come back and re-do it every year or so.
The problem in both these cases of Asphalt and Line markings is, I suspect, 'false economy' (as usual in Britain).
From what I know of the technical specifications given to us by our contractors (currently working as Tier 1 contractor on HE and LA resurfacing packages; used to be a highway engineer for an LA) there hasn't been a change in materials used: it is still molten thermoplastic with colour dyes and glass beads. The most likely culprit is the local authority planning their resurfacing and re-lining works to coincide with the end of financial year chaos which results from the councillors not permitting any spending until the 11th hour - the issue there is you are laying in cold and/or wet conditions which causes the thermoplastic to either break up or not bond with the road surface and shatter off in chunks.
Ideally you want to be lining in summer when conditions are dry and hot, and resurfacing in spring or autumn when temperatures are warm but not overly so to cause melting. However what normally happens is everything gets hit just before Christmas, then they have a breather to see how much is left in the pot and have a mad dash in February and March when conditions are against them.
Yes, that sounds right, (although the guy did tell me the formulae had changed) and I've certainly noticed it more these last ten years though or maybe longer. Maybe the organisation has just got worse. And yes, the local authority here IS useless so that could well be it.
On a recent driving holiday in Chile I noted that most of their roads are concrete but are very smooth without any excessive noise and thumps from the expansion joints. No idea how these are made but the technology to make concrete acceptable certainly exists.
So THAT explains the "thumpthumpthump" round the M25 between Potters Bar and (I think) Waltham Cross.
There are definitely uses for concrete pavement - if you have really heavy use, concrete pavement is definitely worth it. Where I live (not in the UK) nearly all new roads are made in concrete, and we often put a bit of tarmac over it after a while so it's not as expensive. Every now and then the tarmac bit just gets scratched out and replaced again. Trucks here are not exactly compliant to weight limit regulations, and traffic is almost always heavy.
The A90 at Brechin has a Concrete surface from mid 1994 I think and famously the M90 was the first with Unreinforced concrete slabs. Certainly remember driving on that. I think there’s also a wee bit on the A1 at Dunbar where it drops to single carriageway...
Much of the M31 Hume Motorway between Albury and Murulan (a distance of 400km) in New South Wales is concrete. When you cross the border from Victoria, the sound is immediately noticeable. It is a reinforced concrete pavement with verticle (in line with the direction of the road) grooves. I've travelled this route half a dozen times in the past 5 years and although a lot of it is less than 10 years old, I noticed a lot of deterioration in the surface.
I remember going to Oz in the late 90s and being fascinated by the roads, streets and houses there. I'd never been to a 'modern/new' country like Australia or the U.S and for someone used to narrow, twisty roads and cramped houses, it was great. Wide junctions with loads of room to turn and and straight, grid-system roads. I remember one Sunday going for a long walk around Perth and I walked for miles. All the pavements (sidewalks) were gleaming, smooth white concrete (not crumbly, potholed black asphalt (like most of England) and even in the suburbs there were roads so wide you could turn an artic around in one go. (I think most of the roads in the suburbs were asphalt though). Also, I think this was the first place I saw red and amber direction arrows on traffic lights. We only have green ones in England. (That's another topic though I suppose!)
I remember when the A2 Dartford bypass (from the top of Bean cutting to beyond Dartford Heath) was built in 1972. The concrete surface screamed at speeds of 60-70 mph, but was quieter at about 80. Remember - no maximum speed limit then, before the 1974 oil crisis.
The 70mph National Speed Limit was introduced in December 1965, so it had been in place six or seven years by that time! The oil crisis saw it temporarily reduced to 50mph.
Are you sure Chris? That's not what the RAC says in its report on speed limits
See https://www.racfoundation.org/wp-content/uploads/2017/11/speed_limits-b…, section 4.1, page 20
My comment related to the A2, marked with what we now call NSL signs (then called End of Maximum Speed Limit signs).
I’ve read original documents at the National Archives about the introduction of the (then experimental) National Speed Limit in 1965. I’d have to go back to my notes for more detail but it was my understanding that all roads were subject to the new limit in 1965, not just motorways.
That aside, even your RAC report says the National Speed Limit came in in 1967, so either way your brand new section of A2 was not derestricted in 1972!
The big thing with concrete motorways is how extremely hard wearing they are, they shrug off decade after decade after decade of heavy use, whereas a tarmac motorway would have to be resurfaced repeatedly, along with all the road works, traffic jams, delays, etc., not to mention all the extra money needed.
Appears I am the only one who actually enjoys, dare I say anticipates, driving on a ribbed concrete surface. I regularly drive on the M20, between junctions 8-9 and it’s the highlight of most of my journeys. So much so, I turn down the radio and just listen to the rotation of the tyres against the concrete, the bumps etc. Very nice
Then you are a true car-a-holic. Nevertheless, I don't find concrete roads that bad... and though they may not sound very good, they look more 'exotic' than a tarmac road.
You'll love the A50 between Stoke-on-Trent and the M1 then ! You won't need to turn the radio down.
Great article, here in Leicestershire the stretch of A46 linking Leicester with Nottingham is concrete and has sat virtually untouched since 1948.
The A46 Western Bypass is tarmac opened in 1995 and is subject to constant maintenance.
Just had a look at that. Is it really that old? Looks in very good condition. 73 years!
I was looking at the M3 on streetview (which isn't a motorway I've used very much), between Popham and Winchester services and it seems to be a very good concrete surface from what I can tell. I think this was laid around 1985, so 36 years ago now. If it is indeed still of good quality and hasn't had to have any work done since then, I wonder how many times an asphalt surface would have had to be renewed over that time on such a busy motorway?
Since concrete is pretty hard wearing, wouldn't concrete be a suitable candidate on smaller street roads? Since in a residential area you aren't going fast and the noise would be more tolerable compared to potholes
I think there are two points to consider with your idea; First, BECAUSE vehicles aren't moving at high speed in a residential area it shouldn't need concrete (IF the surface has been layed competently) and second, this being Britain, even brand new estates often have the roads dug up within a few months (or even weeks) to repair/relay services. Also, concrete, apart from being more difficult to dig up, can't be driven/walked on for a good day or two. So they would just end up doing what they do in my town, whether they're repairing block-paving/slabs/concrete which is sling some 'instamac' in it anyway. However I DO think they should fix problem pot-holes with a good foot of concrete before laying the asphalt on top. They have been out to one near me many,many times over the years and within a month the asphalt just sinks and crumbles away. It's almost as if they just use black gravel without any asphalt cement in it these days.
Bit late to this (only just discovered the article);
From memory, I can remember several residential streets in the South East of England being concrete, in particular, one in Findon Valley near Worthing being resurfaced with tarmac and the residents being extremely happy about it.
So, there were several in Haywards Heath, Cuckfield and Balcombe, Shoreham, Eastbourne and the industrial estate, Manor Royal, in Crawley.
Interestingly, at least one, Bruce Close in Haywards Heath, was unadopted.
Drove a car I bought from a relative through the SW section of the M25 for the first time and was startled by the rumbling and moaning noises, like many others I thought the rhythmic thumping was a flat tyre. After owning the car a short time I noticed some of the tyre tread depths were getting close to minimum and I had to Google the brand names (they turned out to be of the budget variety) so I decided to replace them all for Dunlop’s. The next time I drove on that section of the M25 the difference was amazing, hardly any road noise and the thumping which previously shook the whole car could barely be felt through the steering wheel. I’m not making excuses for the concrete surface, it’s pretty poor, but good quality tyres at the correct pressure can really make a difference.
They also seem to be replacing chunks of the A180 between Barnetby and Grimsby with tarmac, though it seems quite haphazard.
There's a different problem with some asphalt (Tarmac) surfaces, which you don't get with concrete. Many sections of motorways have shallow trenches along them (in the direction of travel), particularly in lane 1. Presumably this is subsidence under the weight of HGVs. I've often wondered if it's due to reopening the lane too soon after resurfacing / rebuilding.
I think it's just the sheer weight of HGV's continually wearing it down. I've thought before that lane 1 could be done in concrete even if the other lanes aren't. The same with junctions, where traffic is continually stopping, starting and turning. They already do this in some parts of the world, (I've seen it in Los Angeles for eg) where asphalt would be soon churned up due to turning vehicles. The different colour of the concrete (ie lighter) can also act as a visual 'warning' to drivers that a junction is ahead.
Yes, tarmac is every so slightly pliable so over times flows away from where the trucks run. Once there are ruts the trucks then run in them making it worse.
It is quite usual in industrial estates to do areas around loading bays in concrete as trucks manoeuvre there, but elsewhere in tarmac. Concrete is way more expensive initially, hence the mix. Why this has never caught on with motorways though I don't know. I imagine doing lane 1 in concrete and lanes 2 and 3 in tarmac would, over time, lead to a step between the concrete and the tarmac?
I expect that’s the reason - getting a longitudinal joint between concrete and tarmac that would, over the long term, remain level and safe enough for 70mph running would be virtually impossible given the different properties of the two surfaces.
Damian and Chris (apologies, I posted as 'anonymous' by mistake); Yes, you could both be correct there I suppose.
Someone has mentioned about how concrete becomes more and more stronger with time. In fact most military airfields have concrete thresholds that were put down in wwii and havent been touched since. And of course civilian airports also have concrete thresholds and also conrete parking areas. The reason for concrete parking areas is for the same reason that petrol station forecourts are concrete, fuel and tarmac dont mix very well. How often do motorways need resurfacing after a major fuel spillage? On the other hand concrete does tend to absorb spilt fuel and then release it when it gets wet, how many of use have come a cropper when walking on a wet petrol station forecourt?
As for concrete roads these are or were quite common on a lot of armed forces married quarters estates, Im guessing to save money on tarmac. And as for the grooves in the concrete airfields do the same in the tarmac on runways, its called the friction course and I believe its an aid to aircraft braking.
I should also mention that in Germany the hard shoulders on autobahns were concrete, this was apparently for tanks to travel on in wartime.
Something I forgot to mention was "bostik concrete". This was a form of very quick drying (15 minutes) concrete that was invented by the Royal Engineers for use on airfields during the cold war. The Royal Engineers were responsible for what was called "airfield damage repair" and this was invented so that airfields could be rapidly brought back in to use after an air raid. I havent heard of it being used for anything other that airfields.
30 years of the A14!
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- 172 miles of concrete trunk road, motorists mistake noise for mechanical problem: Paton, G. "End of the road for concrete on the motorway", The Times, 11/12/17.
- Introduction of whisper concrete: Wolmar, C. "'Whisper concrete' cuts roar of traffic", The Independent, 23/05/96.
- Diamond grinding: Diamond Grinding of Pavement; UK technique and benefits: Britpave News: Roads get grinding and grooving [PDF]. (2010)
- 2009 diamond grinding trial results: Sanders, P.D. and Viner, H. (2009) Frictional properties of longitudinally diamond ground concrete on the A12 Chelmsford bypass.
- TRL report into 2009-2012 trials: Sanders, P.D. (2012) Published Project Report PPR607: Long term friction performance of longitudinally diamond ground concrete [PDF].
- M27 resurfacing decision: Highways England. M27 J4-11 Smart Motorway Newsletter, December 2018.
- The Cement and Concrete Association, Construction of Concrete Roads, undated.
- Photograph of Mickleham By-Pass surfacing taken from The Cement and Concrete Association, Construction of Concrete Roads, and believed to be out of copyright.
- Photograph of A50 at Hilton taken from an original by Malcolm Neal and used under this Creative Commons licence.
- Photograph of road surface after diamond grinding taken from an original by John Roberts and used under this Creative Commons licence.
- Image of trial signage on M1 © 2019 Google.
- Photograph of M25 taken from an original by Julian P Guffogg and used under this Creative Commons licence.