French low ceiling tunnelways of Duplex A86 comfortable to drive, "not claustrophic"

December 24, 2008

Ever since they were first proposed by French toller Cofiroute some (including us) have worried that their low overhead tunnelways (2.57m, 8.4ft, 101 inches) would seem claustrophic and deter customers. The low height is key to the economy of having two levels of roadway and both directions of traffic in the one tunnel tube, and to making the A86 tunnelway project financeable with tolls. Bob Poole is one of the first Americans to have driven in the first segment of the Duplex A86 before the opening. He has just returned from a visit as a guest of Cofiroute and he says the low ceiling is quite comfortable.

(Cofiroute has added Duplex as a prefix to what was previously known simply as the A86W tunnel to emphasize the doubledeck feature with the two directions of traffic on different levels within the one tube in the innovatory underground roadway project west of Paris.)

Poole says after driving in the first 4.5km (2.8 mile) long segment: "It did not seem claustrophobic at all. They've thought hard about lighting, colors, and finishes to make it visually appealing, and I think they've succeeded."

From his pictures it seems the walls and floor are emphasized with a fine finish, with color and lighting while the ceiling itself is de-emphasized by being left grey concrete without direct lighting.

The ceiling height is not very different from that which is common in multideck parking garages in the US and elsewhere, but there no effort is made to accommodate regular driving speeds.

Maximum speeds posted in the Duplex A86 tunnelway will be 70km/hr (43mph).

The upper deck is northbound Velizy to Rueil and the lower deck is soutbound Rueil - Velizy. (Sometimes the southern end is called Pont Colbert rather than Velizy and the full name for the northern end is Le Raccordement de Rueil-Malmaison, but english speakers can just say Rueil or 'rurr' with only a slight hint of an 'l' at the end.)

Cofiroute officials are putting safety ahead of capacity.  Collisions and fires in tunnels can be devastating - as experience in Alps tunnels has shown.  The original plan was to run 3-lanes on each deck in the Duplex A86. This has now been amended to the two slightly wider travel lanes and a narrower continuous breakdown lane the length of the tunnel on each level.

The tunnel has decks with a usable width of 8.72m (28.6ft) which is striped for opening with two travel lanes of 3m each (9.82ft, 118 inches) with a continuous 2.5m (8.2ft, 98.4 inches) breakdown shoulder and 0.22m (9 inch) offset. Cofiroute officials have said they might in the future reconsider  their striping of the pavement for three travel lanes each deck. But with the 0.22m offset each side these would be only 2.83m (9.3ft, 112 inches) wide.

As a safety measure the Duplex A86W has the two decks as separate self-contained units each with dedicated power supplies, operating systems, and ventilation, and heavy-doored refuges and access stairs between the two levels every 200m (656ft).  There is an access shaft with stairs and an elevator to the surface every kilometer (3280ft). A water misting system is designed to damp any fire immediately, while emergency crews with special low height vehicles are planed to be able to access a fire anywhere in less than 5 minutes.

Exclusion of freight vehicles, separation of directions of traffic, the misting system, more frequent refuges and escapes, and the continuous breakdown shoulder are all safety advantages the Duplex A86 will have over the Alps tunnels.

Vehicles will be limited by regulation and an overhead bar on entry to 2m (6.6ft, 79 inches). The space to the ceiling itself will provide 57cm (22 inches) for signage and other overhead gear.

Duplex A86W is about 10km (6.2 miles) of underground road long in the planning and construction, the northern 4.5km (2.8 miles) of which are now fitted out and being subjected to extensive testing for a planned opening in June 2009. This goes from Rueil-Malmaison near the Seine to the A13 motorway in Vaucresson Le Chesnay. 

Work is well under way on the section south of the A13 to Velizy/Pont Colbert and due to open in late 2010 or early 2011.

The two sections together will fill the missing link of the A86, the 2nd ring route around Paris, and provide high quality road north-south through the Versailles palace and associated woods and estates. The tunnel is 15m to 90m (50ft to 300ft) below the surface.

In June traffic will use a midway interchange at the A13, the interchange largely underground which Poole says is amazingly compact - because of low speed design, grades and tight curvature.

Cofiroute's concession provides for construction of a second tunnelway for full height vehicles after the opening of the two level or duplex facility. The high vehicles tunnel will be the same diameter tube but a single level and one lane each direction. It will trend southwest  to join the A12 some miles west of the route of the duplex tunnel and be shorter in length (7.5km, 4.7mi) according to the plan.

Cofiroute officials have taken to publishing maps of the project without the second full height vehicles tunnel being shown and they call the project "under study." With a single lane each direction and trucks it may never be built.

Variable toll rates

The Duplex A86 will use variable toll rates to manage traffic flows and there will be frequent user discounts of up to 35%. Tolls are expected to vary between E2 and E7 (about $3 to $10). The financial model assumes motorists will pay E6 ($8.40) to E7 ($10) to save 20 minutes in peakhours or E18/hr to E21/hr ($25 to $30/hour of time saved). Trips that now take 30 to 45 minutes on heavily overloaded signalized and roundabouted surface roads will take little more than 10 minutes in the underground expressway.

It is hoped to have average daily traffic in the first full year (2010) of about 40k.

Cost of the project is currently put at E1.7b ($2.4b). Counted as 40 lane-km (25 lane-miles) that is $60m/lane-km or $96m/lane-mile.

Tunnel boring machine

Construction uses a tunnel boring machine (TBM), a huge assemblage (11.57m diameter, 200m long, 2,500t weight) that cuts a circular section through all kinds of rock and earth, delivers the spoil to waiting dump trucks and installs precast concrete segments, progressively building a structural tube as it advances. The A86W tunnel size was set about 15 years ago to the largest then designed TBM with a shield of 11.57m producing an inside tube of 10.4m (34.1ft) diamater.

Newer tunnel designs

There are now TBMs with cutting shields 15.2m (50ft) diameter in Spain (M30,) and 15.43m (50.6ft) across in Shanghai. The 15.43m shield TBM allows an internal diameter tube to be built of 13.7m (45ft). Under the Yangtze River in Shanghai this TBM is being used for three expressway lanes for full height vehicles with space for a  single rail transit track underneath. Two separate tubes have been built for a 2x3 lane expressway and 2-track rail facility. The Shanghai Yangte River tunnel is 8.9km (5.5 miles) long.

A slow, slow project

Cofiroute was formed by 6 construction companies and 2 banks in 1970 but it is now owned by two construction companies Vinci 83%, Colas 17%.  The company obtained an initial 450km of toll motorway concessions of 42 years (1970- 2012). There have been 12 major amendments to the initial concession contract which now covers 1,100km of tollroad the concession extended 18 years to 2030.

Operating a bunch of toll motorways west of Paris Cofiroute had revenue in 2007 was E1038m ($1450m).

The A86W project as a bored tunnel was an unsolicited proposal by Cofiroute in 1988 after a long period of political conflict over construction by the state of a conventional depressed or cut & cover motorway through the Versailles area.

The Duplex project has been long drawn out.

The first A86W concession was signed after competitive bids in 1989. Major construction began in 1997 but in 1998 the concessionw was successfully challenged in the courts for a violation by the French government of European Union contracting rules.

All work stopped and the project was rebid. Cofiroute won again and a second concession was signed in 1999.  Major work was restarted in 2000 and Cofiroute said the first segment to the A13 would open in 2005. Accidents involving major fires in the Alps tunnels led to the addition of extra safety features to the A86W after construction was well under way, contributing to the delays.

Cofiroute has a concession term for 70 years of tolling from opening date.  The company has accepted full design, construction, financing, operations and maintenance responsibilities and the traffic and revenue risks while being contractually protected against unilateral changes in rules. There is no government funding of the major tunnel works, although local governments (communes) are building ancillary bike and hiking trails and doing landscaping.

Aims of the project are to complete the A86 ring route and provide high quality north-south connectivity to the west of Paris avoiding encroachment on the historic Versailles Palace area and the surrounding forests and estates. Traffic from rural lanes and busy suburban surface roads will be attracted to the tunnelway.

Networks of low clearance underground roads

As far back as 1988 there was a proposal for using the single tube double deck tunnel design similar to the Duplex A86W for a whole toll-financed network of underground roads in Paris called Liaison Automobile Souterraine Express Regionale (LASER) or Subterranean Regional Express Network for Cars.  The rationale for low vehicle height was that 85 to 90% of vehicles are under 2m (6.5ft, 79 inches) and there are huge construction savings by building to a 3m lane width and 2.5m (8.2ft) ceiling and designing curvatures and grades for the  capabilities of cars while leaving other vehicles on surface roads and conventional expressways.

LASER would link main activity centers such as business nodes, airports, train stations with light vehicle interchanges to urban arterials and underground parking structures, making use of the double deck format to simplify interchanges, and having the steeper grades and tight curvature possible by excluding trucks.

Comparative heights

Multi-deck parking garages in the US usually have vehicle height limits between 1.98m (6.5ft) and 2.44m (8ft) with the overhead beams 8ft (2.44m) to 9ft (2.74m) from the floor - very similar dimensions to those of the Duplex A86.

Tractor trailers in the US are commonly 3.96m (13ft) and many states allow 4.1m (13.5ft) Bridges and tunnels are commonly built to 5m (16.4ft) overhead clearance to allow a meter (3ft+) above the highest vehicles.

In Europe heavy trucks up to 4.65m (15.25ft) are being catered for in new facilities though for international travel through older facilities they are limited to 4m (13.1ft) height.  The City of Dublin, Ireland was questioned for building their port tunnel to 4.9m (16.1ft) ceilings with a 4.65m (15.25ft) height limit on the basis that higher trucks are coming. The Miami Florida port tunnel was recently designed to a 5.03m (16.5ft) truck height. That 5.03m (16.5ft) is a common height for new expressway standard road facilities in the US.


TOLLROADSnews 2008-12-23

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