Highway Investment Programme Details
Worst road first
Elton Lane was ranked as the second worst road in the Borough. The survey said that 82% of the carriageway was in red condition and in real need of repair with 16% in amber condition approaching failure and only 2% in the green condition of needing no work undertaking.
Road condition inspections
We use a road condition machine which is a Transit sized van with laser scanners mounted at the back to scan the road surface. The machine collects the following data at a normal road speed of 50mph.
- 3-Dimensional spatial co-ordinates
- road geometry
- survey speed
- longitudinal profile
- wheel path rutting
- texture profile
From this data over the whole of the A, B and C network the roads are defined under three headings.
- Green is in good condition needing no immediate work
- Amber is showing signs of failure such as minor cracking or wheel track deformation
- Red is in need of urgent repair
Surface dressing consists of a bitumen emulsion with stone chippings applied to the surface. This effectively seals the surface from water and prevents the freeze-thaw action that breaks up carriageways.
Water is the real enemy of road pavements as the change from liquid to ice in the cold includes an increase in volume which can deform the road structure and is one of the main sources for potholes. If the surface is effectively waterproofed and drained the detrimental effects of creating can be minimised.
The second most important part of the road is the surface and the skidding resistance that is generated between the tyres and the carriageway. The application of the stone chippings effectively enhances the road surface and reinvigorates the skidding resistance.
The picture illustrates the process on a dual carriageway in July (surface dressing has to be carried out in the warm dry temperatures of summer).
- traffic management is installed in this case moving traffic to the nearside lane on both sides of the carriageway. This would start after the peak hour to minimise traffic delays
- the road surface is swept clean
- the front tanker applies the binder which is polymer modified to enhance its properties
- the front stone chipping spreader lays 14mm chippings
- the second binder is applied
- the second layer of chippings are 6mm to integrate with the first layer of 14mm stone, this second coat is not usually applied to lanes but always on major roads
- the surface is rolled by a pneumatic tyred roller
- the surface is swept clean and the binder is given time to generate its adhesion
- traffic is allowed onto the surface with a 20mph speed limit. The action of the slow speed traffic effectively applies the final finish to the surface
- the road is swept again to remove surplus chippings as required but always a week later
How we sweep the chippings and add white lines to surface dressing
The Surface Dressing is swept at four distinct times:
- immediately after the surface dressing and before traffic is allowed onto the surface.
- traffic is permitted to drive on the new surface but there is a 20mph speed limit to avoid flying stone chippings
- after 24 hours a second sweep removes surplus chippings and traffic can travel a little faster
- after 48 hours the surface is bedding down and it may be possible to install the white lines.
- white lines will be installed such as double white lines, give way lines and stop lines
- after 7 days the final sweep takes place and then the white lines are completed throughout
The bedding of the chippings into the carriageway surface continues under the action of traffic for some considerable time. In the case of work carried out at the end of August the bedding process will continue throughout the winter.
Micro asphalt is a slurry seal comprising of a mixture of materials
- aggregates – a combination of coarse and fine depending on the carriageway usage
- emulsion – usually a polymer modified bituminous (PMB) emulsion
- cement or hydrated lime
- chemical ‘breaking’ agent
- fibres can be added for additional structural integrity generally on heavily trafficked A roads
The materials are blended on site in a specialist piece of equipment – a self-propelled micro-asphalt paver. It is laid in two layers each of about 5mm thickness. The first layer acts as a regulating course and the second provides the finished surface with skidding resistance and surface texture. The material gains in strength as it matures and it is possible to be trafficked very quickly.
Re-surfacing with an asphalt inlay/overlay
Simple re-surfacing consists of adding a new surfacing layer above the existing carriageway. This can be done on rural roads where there are no kerbs or adjacent properties but often it is necessary to remove the existing surface and replace it. The first option is an Overlay and the second is an Inlay.
The picture shows the new surface layer being installed and rolled. This is almost always laid in the direction of traffic and the new hot surface has to cool to gain strength.
The road is closed for the works to prevent cars and lorries driving on the new surface. The opposing carriageway to the right has been planed using a cold milling machine and the kerbs remain in place. The material is normally a hot-rolled asphalt with polymer modified binder. In essence it is graded stone coated in bituminous binder and mixed together in a hot oven. The stone creates the skidding resistant surface and the surface is generally quiet.
How diversion routes get designed
Diversion routes have to cater for every type of vehicle that could be expected on the road that is closed. This means that a normal road cannot divert traffic onto a motorway because combine harvesters and push bikes are not allowed onto a motorway.
In practice this means that the signed diversion for an A class road cannot divert traffic onto a B or C class road.
The example below shows the diversion for works on Wrexham Road at Burland and the signed diversion is on A49 and A51. If you are in a car and know the area there are a few little lanes that you can use to sneak round the works. We tell HGVs not to use their SatNav but to follow the diversion, even so the little lanes have more traffic than usual.
How do residents get into the road closure?
When roads are closed for surfacing residents can still gain access through the works. There may be works going on which may cause a problem but the Traffic Management Gatekeepers will be able to advise people. If you live along the route they will open the cones and tell you how to drive through safely to your home or business.
A working site is a potentially hazardous location and the Gatekeepers can offer advice on how long it will be until it is safe to travel through the site and there may be occasions when it would be quicker to go round the diversion route.
It is also worth noting that the new surface can be damaged before the temperature of the material falls and drivers may be asked to travel with hazard lights flashing on the opposing carriageway.