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Lane logistics

Highways M25 widening

Work on widening one of the busiest roads in Europe - the M25 - started in earnest this week.

Mark Hansford reports.

From a civil engineering point of view, widening 10.5km of the M25 between its interchanges with the M3 and M4 is a doddle. No additional land take and no widening of existing underbridges is required. In fact, the only work that breaks into virgin territory is a short spur to the new terminal at Heathrow Airport.

But from a logistics and traffic management viewpoint it is a different matter entirely. This section of the M25 is one the busiest roads in Europe, carrying 240,000 vehicles a day. If each one of these vehicles can shave five minutes off its journey the saving to UK plc has been estimated at £240,000/day. The scheme would pay for itself in 21 months. No other road in Britain comes close in terms of volumes of traffic carried and strategic importance.

Looming in the back of the minds of those responsible is the anxiety that, if this goes wrong, public and political support for other planned widening schemes could disappear in a flash.

'We are the vanguard of future motorway widening. The success of this could determine the outcome of the 10 year plan, ' says Highways Agency project leader Terry Williams. 'It's got to be a success and we will make sure that it is.'

The job of widening this crucial section from junction 12 to 15 has fallen to contractor Balfour Beatty, which won the £148M design and build contract in May last year. Project director Peter Anderson echoes Williams' view. 'Future widening work could depend on this project being a success, and as civil engineers that widening work is vital to us.'

Balfour Beatty won the job after a five way battle, no doubt helped by its previous experience of working on the road. It was responsible for building the original southern end of this section and, subsequently, for its widening in the late 1980s.

The decision to widen this section again was made by then transport secretary John Prescott in March 1997. However, to avoid repeat disruption to motorists and local residents, the Highways Agency decided to defer the widening until a planning decision had been made on Heathrow Terminal 5, now well into its construction phase.

The M25 will be widened from four to five lanes in each direction over the 7km stretch between junctions 12 and 14, and from four to six lanes in each direction over the 3.5km stretch between junctions 14 and 15.

The work will also include a spur road into Terminal 5 from a freeflow interchange at junction 14, paid for by airport operator BAA.

Work will take place over the next two years in two sections - junctions 12 to 14 and junctions 14 to 15 - and in five phases.

Phase one - preparatory work to construct the crossovers for the contraflow - began on 5 January and is already completed.

The switch to contraflow took place at the weekend. With hard shoulders pressed into operation the full four lanes will operate in both directions throughout the works - minimising traffic disruption (see box).

Phase two began on Monday, with Balfour Beatty taking possession of the southbound verge between junctions 12 and 14.

Eighteen weeks of widening follows, with steepened embankments, piled retaining walls and a P6 parapet added to a railway underbridge all allowing the widening within existing boundaries.

Phase three sees work switch to the northbound carriageway for another 18 weeks, concluding in September. Traffic is then taken out of contraflow, but still pushed on to the hard shoulder, so that the central reservation can be narrowed.

With work between junctions 12 and 14 complete, work shifts north to junctions 14-15 for phases four and five. Using the same sequence, this section is scheduled for completion on 19 September 2005.

Work on the M25 spur into T5 will take place as the contract progresses. The spur sliproads will be built before the main widening work moves to the junction 14-15 section and be used as a temporary fourth lane.

Flow chart

Keeping traffic moving throughout the duration of the works is a top priority. Three years of planning has gone into ensuring that traffic chaos is not allowed to scare government off committing to further widening programmes.

It is no small task, says Williams. 'It's not just the 200,000 vehicles a day. We have two motorway interchanges at each end and two trunk road junctions between, so a high percentage of traffic is joining and leaving at all times.'

At the M4/M25 junction, for example, 50% of traffic on the two roads swaps. Up to 30% does the same at the M3/M25 interchange.

Traffic flow will be difficult to maintain.

To this end, the same number of lanes as exist at the moment - four lanes in each direction - will be available throughout the works, albeit they will be narrower and there will be a 40mph speed limit.

The speed limit is there entirely for the safety of motorists and construction workers but early signs are of another benefit - traffic flows have improved under the controlled conditions.

Of course, without hard shoulders, problems will quickly escalate and for that reason incident support vehicles are on permanent standby.

'The key to this project is maintaining free-flowing traffic, ' says Anderson. 'We have 110 CCTV cameras to give us full coverage of the network.

These cameras are monitored 24 hours a day so we will see incidents as they happen and mobilise vehicle recovery. The emphasis has to be to remove the blockage ASAP.'

Balfour Beatty will be using an innovative buffer lane throughout the course of the roadworks to separate the contraflow lane from oncoming traffic, reducing the risk of head on collisions, offering emergency and recovery vehicles swift access to incidents, and providing vehicles in the contraflow lane with a route around stricken vehicles.

In addition, both the contraflow lane and work sites will be protected by temporary steel or concrete barriers.

Who's who

Joint client: Highways Agency/BAA

Design and build contractor: Balfour Beatty

Contractor's designer: Gifford WSP

Client's designer: Atkins

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