Linking Newark, Leicester and Lincoln, the A46 is a lifeline in the East Midlands of England, Yet it has always been plagued by congestion and an above-average accident rate.
UK Highways Agency figures showed daily traffic flow was over-capacity for 94% of the time and nearly a quarter of that traffic was HGVs. Over the years much of it has been upgraded to dual carriageway, but one last 28km section from Newark to Widmerpool remained untouched.
In planning since 2004, the previous Labour government gave the go-ahead for the final part of the upgrade in November 2008 as part of the financial stimulus package for the economy. Very little of the old road could be retained, so the project would need to be nearly all newly-built road. Balfour were awarded the contract and bought in Lafarge to handle the four-layer, 330 specification road surfacing.
They were keen to get away from the traditional method of using 10m spaced pins and used this project to evaluate Topcon’s mmGPS system as a replacement. Contractor Richard Bows explains that “pins create a lot of work – for this 26,000m stretch of road we’d need 10,400 pins. 800 pins usually take two engineers six to eight hours, so that could be 208 man-hours. Then there’s their setup and maintenance, usually about one in five will need resetting at some point.” They used the Topcon’s mmGPS paving system to put down the two base layers, alongside 10m pins to measure accuracy.
“Phenomenal” is the word Richard uses to describe the results, “It is the future.” In comparing the two methods he is confident in the capabilities of mmGPS: “when we did encounter discrepancies in the measurements between the pins and the GPS and re-measured, we tended to find it was the pins that were wrong. There were a few points when we found that if we’d kept on with the measurements from the pins, the road wouldn’t have been wide enough. When we are just using pins we are kind of blind in between them too, so there could be 30mm dips or humps, but that’s not a problem with mmGPS.
“Once our crews had the plan of the site they only needed the normal 100m control pins to work from. Depending on the sub-base we could estimate how much material we would need for each layer much more precisely and it improved ride-ability hugely because the lower layers were as good as the top ones.”
In the UK, the Highways Agency currently only approves the traditional pin method, but Richard expects this to change quickly, especially after results like these. After this project he feels the Topcon mmGPS has more than proved itself and he would push to use this system over pins every time. In his own words, “I’m confident that with this system we can meet and even exceed the standards for major road building in the UK, and it will significantly reduce costs.”