Refurbishment of a key stretch of trunk road, including resurfacing and bridge maintenance to current standards while maintaining large traffic flows into London, presents quite a challenge. Managing disruption caused by accidents and vehicle breakdowns adds to the difficulties facing construction teams.
The Highways Agency commissioned contractor Fitzpatrick to carry out major maintenance of a busy 4.5km stretch of the heavily trafficked A12 immediately east of junction 28 of the M25 between January and the end of May this year. The project team completed the scheme on time and, using a complex sequence of traffic management phasing designed by consultant Owen Williams, traffic flows were maintained.
Around 70,000 vehicles a day use this section of the A12, according to the Agency's annual average daily total statistics, putting it among the busiest stretches of the UK's roads.
The original reinforced concrete carriageway was built in 1964 and deterioration earmarked it for major maintenance despite previous joint repairs and surface dressing. The carriageway has been refurbished using the now common method of saw, crack and seat with an asphalt overlay consisting of around 150mm of road base and base course with a 30mm layer of RMC's Viatex low noise thin surfacing.
Fitzpatrick has also carried out substantial bridge maintenance (see box), constructed new slipform concrete channel and replaced damaged concrete subsurface road drainage with plastic carrier drain.
Widening the road was crucial for the project and forms a key aspect of the Agency's plans for future maintenance. The original 7.3m wide dual carriageway has been extended on each side to provide additional 1.8m verge hardstrips and an extra 0.6m clearance between the white line and central reserve.
The added width enabled Fitzpatrick to maintain required contraflow lanes during construction and has left room for the same traffic management when the road is resurfaced.
'Minimising disruption is quite a big issue and there is a limit to what can be done to keep traffic flowing at all times, ' says Highways Agency project sponsor Julian O'Dell.
'However, I think we got the traffic management about right and we will be using a similar arrangement when we start the same work on the next stretch of A12 next year.
'Now the scheme is finished, most people are surprised to see just two lane dual carriageway after we appeared to be adding another lane, ' he continues.
'The extra hard strips and clearance to the central reserve has made the road safer for drivers and maintenance contractors. Enough lanes can now be kept open to enable future work to be carried out during the day.'
The traffic management sequence was operated by subcontractor Associated Asphalt to maintain tidal traffic flow.
Fitzpatrick's first major task after carrying out service diversions was to add 2.5m of running room to the verge side of the London bound carriageway. This allowed operation of a four lane tidal contraflow while one lane was left closed.
Three lanes were dedicated to London bound traffic from 5am to 10am, after which a second lane was closed and the tidal flow switched to leave one lane heading towards London and the M25 junction and two eastwards towards Ipswich.
This arrangement remained in place until 9.30pm when a third lane was closed, leaving one lane operating in each direction. This gave the contractor all but two lanes to work on until 5am the following morning, and during weekends when the same two lane contraflow was in place.
'We had to work like crazy over the weekends to ensure we met the programme, ' says Fitzpatrick project manager Dick Watts. 'The team has done well to get the job finished on time because although a second lane was closed after 10am, we effectively had only one whole lane available all day.
O'Dell says the longest recorded delays of around 20 minutes tended to occur for a period just after the traffic management system was switched to leave only one London bound lane, while traffic volumes were still relatively high. Speed restrictions of 40mph through the contraflow were enforced with TASCARs (temporary automatic speed cameras) and CCTV was used to provide 24 hour traffic monitoring of the whole site.
Speed cameras, required and operated by Essex Police, were provided by the Highways Agency, while CCTV coverage was supplied by specialist Graham Firth Communications.