Is injection the solution to the UK's pothole pandemic?

Recent figures from the RAC show that the UK has a major pothole problem – and one that is getting worse. 

In the last 3 months of 2019, the RAC attended 20% more vehicle breakdowns related to potholes than in the same period a year before, and more than 2,000 drivers experienced a breakdown due to potholes.

Potholes are a serious issue: they can cause damage to wheels; break suspension springs; damage shock absorbers as cars pass over them; cause collisions as vehicles swerve to avoid the obstacle;^[1] and contribute to serious road accidents.[2]

The hidden cost of potholes

Despite paying £40bn in motoring-related tax each year, Britain's drivers still do not have access to roads that are wholly smooth and safe. Each year the nation's drivers spend around £4.09bn repairing damage to vehicles caused by potholes.

More than half (56%) of motorists say their cars have been damaged by potholes, with the average annual cost per person amounting to £230. More than 40% of UK drivers say they would be willing to pay more car tax or road tolls if it contributed to tackling potholes.^[3]

The national pothole lottery

Some areas of the country have a much bigger pothole problem than others. According to a recent study by the County Councils Network, funding varies widely throughout the country, with London swallowing a disproportionately high level of funding.

Some London boroughs spend more than £62,350 per mile of road each year, on average, whereas 'shire counties' spend an average of under £20,885 per mile – nearly three times less.

Roads outside the capital are also in need of additional funding. In 2018, 730 miles of road in London (or 8% of the total mileage) were found to be in need of repair 'at some point in the near future'. In shire counties, 11,117 miles of road (9% of the total network) were in need of patching.^[4]

Cash-strapped councils

Financial pressure means that councils have to make difficult decisions about how to allocate resources. Much of the £24.5m spent by councils in 2017/18 went on cheaper short-term repairs to 'patch and mend', rather than on longer-term fixes, according to a survey from the Asphalt Industry Alliance.^[5]

Spending on potholes is increasing, and a pothole is now fixed in the UK every 17 seconds. The Department for Transport has announced a £201m spending spree to resurface 1,000 miles of road, although industry figures say this is far short of the total required to bring the road network up to higher levels of quality.^[6]

Spray injection: the future of pothole repair?

A method that offers a quicker, cleaner and cheaper repair of potholes without compromising quality and durability is sure to be welcomed by motorists and councils alike, and the spray injection method offers many advantages over typical repairs.

Traditional pothole repair typically involves the use of jackhammers or saw cutting to create a straight edge, the excavation of the surrounding area and the application of hot mix asphalt, then a delay until the surface is capable of receiving traffic.

Injection repair is up to 80% cheaper than conventional repair. The pothole is blasted with compressed air to remove debris and clean the surface. The void is sprayed and coated with bitumen emulsion, then cold emulsion asphalt is injected into the void. The hole fills from the bottom up, so no additional compaction is needed.^[7]

The injection process is not only cheaper but also less labour intensive and hazardous, as no hand-arm vibration is involved for contractors and very little dust or noise is produced. There is no waste material and the carbon footprint is lower than for conventional repair.

A new standard to support spray injection

Naturally, those involved in road repair will want to be sure the new method is as efficient and as reliable as possible. To assist with this, BSI has produced BS 10947:2019, Spray injection patching for highways and other paved areas – Specification, which sets out the first standard specification specifically for spray injection patching.

A central feature of the standard is a core end-performance requirement that the surface profile of the treated area must be substantially similar to the surrounding road surface 1 year after installation.

Also included in the standard are definitions of technical terms such as:

• adhesion;
• aggregate;
• binder;
• bitumen;
• bitumen – modified;
• bitumen – emulsion;
• bond;
• break (emulsion);
• breaking behaviour of characteristic emulsion;
• cationic bitumen emulsion;
• durability;
• defect;
• factory production control;
• laying record;
• mix design;
• polished stone value (PSV); and
• quality assurance (QA).

There are also specifications on constituent materials (such as emulsion binders and aggregates); procedure; depth; macrotexture; binder–aggregate adhesivity; product cohesion; surface profile; durability; Type Approval Installation Trial (TAIT); and quality plans.

The new standard is available from the BSI online shop.