Wednesday 14 January 2015

Not The Hole Story

Potholes are always in the news somewhere, but they are merely a symptom of much wider problems with UK infrastructure and that is sweating our assets until they collapse.

Tomorrow is (15th February) is National Pothole Day (#NationalPotholeDay) over on Twitter) organised by the lovely people at Street Repairs which is has a website and app which allows you to report (yes) potholes and other street defects, and why not. You can also follow them on Twitter @StreetRepairs and Facebook if that's your bag. A big Hat Tip to Mr Pothole for alerting me to the event!

Right, plug over, back to the post. You don't need me to tell you what potholes are, but suffice to say, they are symptom of the state of the UK roads. I am also not getting into the debate about who pays for the roads as the answer is clear - we all do; and we all pay when they are not maintained properly and someone gets a claim paid out.

At least for individual council's, the road network is their largest asset. The Whole of Government Accounts (WGA) process valued the country's highway network at £275bn (p209) in 2012/13, although public infrastructure assets are thought to be undervalued by some £200bn and so the figure for the highway asset will be higher. We also have the current ALARM survey which puts the road maintenance backlog at £12bn for England and Wales, but this is just carriageways and doesn't count footways or bridges for example.

Of course, these figures are often educated guesses (with a lot of work to get to them) and so we cannot be completely sure, but clearly, we have allowed an extremely valuable asset to deteriorate through decades of neglect and underfunding. An exercise in work had us value the replacement cost of our entire network at a trillion pounds (digging out and completely rebuilding).

Everyone who travels on the highway network will have their own ingrained locations for road defects on their regular journeys (and if you travel on two-wheels, it is pretty important that you are not thrown off - engine or leg powered alike). The term "pothole" is a proxy for poor surface conditions and there are many theories for the origin of the term - I like the idea that it comes from potters nicking clay from dirt roads to make pots, but who knows for sure. Roads have a history of eons and you could do far worse than reading Carlton Reid's Roads Were Not Built for Cars which has a great history on road construction from animal trackways to more recent times.

For modern roads, we are concerned with supporting the loading from vehicles. We have relatively weak subsoil upon which we (scientifically) pile layers of different materials which get comparatively stronger, thinner and more expensive as we head up to the road surface. For example, a basic residential road is likely to have a layer of pretty course crushed rock, brick, concrete or other materials being relatively cheap. On top of this, a more finely graded layer of crushed rock (up to 75mm in size) and then 2 or three asphalt layers, with the most expensive and thinnest layer being the surface course (concrete is also used of course and also composites of concrete with an asphalt overlay).

I am using fairly general terms here and so for much more detail on everything, I highly recommend the Idiot's Guide To Highway Maintenance for everything you could ever need to know on the subject. The layers of a road is collectively referred to as the "pavement" which shouldn't be confused with the popular term for footway (in the UK, sidewalk elsewhere). The job of the pavement is to conduct the loading from millions of standard axles (a design parameter) down into the subsoil.

For other areas, such as footways and cycletracks, we don't generally need to worry about traffic loading, but the thickness of the "pavement" needs to take into account the methods by which they will be constructed and maintained. In my experience, people are reluctant to construct footways and cycle tracks thick enough and they end up moving and settling with the ground - they need to be as engineered as the bit vehicles are driven on. In terms of "damage" to roads, it is the HGV which does the most - pounding the layers of the pavement. Cars don't do a great deal of damage, but they wear out the surface and of course people walking and cycling don't cause any appreciable damage.

The greatest enemy to the highway engineer is water and we go to great lengths in getting it off the road surface and away. In some cases, we use sub-surface drainage to keep water away from the engineered lower layers of the pavement. Water is a funny substance. You can't compress it and when it freezes, the volume of the solid (ice!) is about 10% greater than the liquid. For roads, this is a problem. If water gets into minute cracks in the road surface and freezes, the expansion will start to fret the edges of the cracks, making them larger and therefore letting more water in. 

The delightful term "mud pumping" is another failure mechanism whereby water in cracks (and joints in the case of concrete roads) displaces fine particles from the underlying pavement materials and the action of the traffic above compresses the road surface (by a small amount). As the road is compressed, the water is squeezed and forced out of the road, carrying fine material because water is not compressible. Over time, the action of the traffic and water can create voids underneath the road surface and we start to see a break up. 

The mechanisms can work together of course and in the case of asphalt layers ("tarmac") if they are not properly bonded, then water slides in between the layers and the traffic action helps to life the surfacing. There are many maintenance issues, but keeping highway drainage clear and free is extremely important. If the water is not draining away, it is helping to destroy the road. If the road surfacing has not been laid properly and puddles are collecting, that is helping to destroy the road - resurfacing to the same levels won't deal with the problem. 

One of the big problems we have is that road drainage is often split between several responsibilities. In urban areas, the gullies and pipes to the main sewer will be managed by the highway authority and the sewers by the sewerage undertaker. In London (for example) this will be the boroughs as highway authorities and (mainly) Thames Water. If the gullies and highway drains are clear, but the sewers are not, we will get flooding and this is a common cause of complaint from local authority staff who know "their" bit is clear.

In rural areas, we can still have highway drains and sewers, but we will be dealing with ditches along the sides of roads in many cases. The highway authority has the right to drain into ditches and to maintain them, but it is quite common for roadside ditches to be part of field drainage with the landowner having responsibility for cleaning. The old fashioned job of "lengthsman" was a highway operative who patrolled a patch undertaking all sorts of minor works which prevented larger problems. For drainage, it could be something as simple as hoicking out something blocking a ditch or clearing grips (little ditches to let water run into bigger ones). Of course, government cuts have seen the demise of this important local highways person.

In trying to keep water out of the surface, we can resurface a road completely which will provide new "waterproofing" for the lower layers (the surface also provides skid resistance for vehicle tyres, especially in the wet). We can surface dress (hated by many bicycle riders) which uses a bitumen binder to seal the surface, prevent oxidisation of the materials below and to provide grip with chippings. Actually, if designed and installed (and cared for afterwards), surface dressing remains an important maintenance technique - it is not surfacing on the cheap as often reported, it is something different.

Of course, if a road becomes so damaged that it is not safe to use, we have powers to place weight restrictions and eventually close it for safety purposes. That is the nub for me really. I have been in the highways game in one shape or form for nearly 20 years, starting out in maintenance as it happens. Maintenance is the Cinderella of highways, but there is tremendous skill and ability out there in keeping our crumbling network together. But miracle workers we are not. Like any maintenance work, if we don't keep at it, then our assets start to break up, we need to invest in our people (both training and paying them fairly) to get the best out of them. 

Despite the promises and the continued funding announcements, are roads are failing with local roads failing most as authorities struggle with the huge level of cuts being made. For our roads, the humble pothole is just the tip of an underfunded iceberg.

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