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Roads; Abu Dhabi highway

Design work for the final stage of upgrading the road linking Abu Dhabi with Dubai is now complete. Subject to approval by the client, the Public Works Department of the Emirate of Abu Dhabi, the contract will go out to tender within the next few months and the entire project should be completed in 2002.

This is a road upgrade with a difference. Completion date is probably less important than quality of design and construction, and integration with the planned development of the fast-growing Emirate. This includes two new cities on either side of the highway and a separate route for lorry traffic.

The existing dual two-lane road is the major highway link between the capital cities. However each year the volume of goods arriving through Jebel Ali port increases and with it the number of trucks carrying the imports to their final destination. Almost certainly a significant proportion are overloaded - especially given the lack of weighbridges in the area - and this pounding has inevitably affected the road surfae.

Car ownership among the resident population is also rising, and at weekends particularly, the volume of leisure traffic is considerable.

The appointment of a consultant for the upgrade was the subject of international competition from which Parkman emerged the winner. A complete consultancy package was required, from a survey and site investigation, following on to design, tender analysis and construction supervision.

The brief called for an upgrade to expressway standards with a design speed of 100km/h and access for local traffic movements. In cross- section the new road was to comprise a dual three-lane carriageway with a 20m central residual median which would be irrigated and planted. The original southbound carriageway was to be widened and the northbound scrapped and replaced.

New grade separated interchanges were needed and the two existing interchanges assessed for modification or redesign. And layout, structures and interchanges all had to be capable of accommodating the addition of a fourth lane in the future.

An initial investigation showed a number of variations in the construction and condition of the road. Settlements have grown up on either side of the 78km length, linked by at-grade junctions and crossroads. Some of these are legitimate - others have simply appeared. Rresearch revealed that the present highway alignment had been built up through a number of contracts - some dating back to 1969.

Given this varied history, it was decided to undertake an aerial photographic survey of the route and because of time constraints use GPS technology for the photogrammetric control. This work was completed in just two weeks using the consultant's in-house GPS receivers and survey staff.

Little useful traffic data existed, so accident data was obtained from the traffic police and counts were made at key locations to model traffic patterns, likely growth and verify highway and junction capacites.

The Emirates region is not renowned for its rainfall, but occasional heavy showers can and do make flash flooding a real threat. However, hydrological studies showed that even without cross culverts, flash flooding was unlikely to cause damage on this route.

The client's brief specified that the design should be carried out to AASHTO standards, which meant Parkman's designers had to familiarise themselves with these. The preliminary design work was carried out in the firm's UK offices using the in-house MOSS system mounted on Hewlett Packard work- stations. Mosscad and Cadmoss, developed by Parkman, were used to generate the large number of design drawings. Direct transfer of design information between the two systems allowed fast preparation of contract and tender drawings.

This computerisation proved to be a major benefit when, at a very late stage in tender document preparation, the client requested a change to a four-lane dual carriageway with a design speed of 120km/h. A complete set of revised documents was produced from the computer set-up without any major delay to the tender process.

This has not been the only design change requested. An interchange at the border with Dubai has been subject to a number of revisions - largely to accommodate the future construction of a dedicated route for goods vehicles. It finally emerged from the design process as a dumbbell type with a bridge. There have also been changes to the number and configuration of the interchanges which include an access to a palace and an underpass to a new camel race track.

A design team is now established in Abu Dhabi to speed the production of these revisions which are not lightly requested and are carefully studied by the client. Indeed the chairman of the Public Works Department, His Highness Sheikh Sultan has visited the project on a number of occasions, even going so far as to drop in, unannounced, on a rather startled Parkman enginer to accept a cup of coffee and find out how work was progressing.

The US$350M (£218.75M)project has been split into six contracts, the first awarded to HILALCO in May 1995. Subsequent contracts went to Admark, Al Muhairy and Bin Hafeez. Two contracts remain to be completed. Al Jaber was due to start work on Contract 1A this month and the final section, Contract 1B, will go out to tender shortly.

The quality of the work is exceptionally high, says Robin Penman, the Parkman engineer directing the project. All bridges are load tested after completion, and a travelling beam checks the accuracy of the road profile. Finish of the piers and abutments on the project's seven bridges is as near perfect as humanly possible, but Penman adds, the contractors appointed are all experienced and used to challenges of working in the area. The key, he has found, is the appointment of a good project manager.

Construction of the interchanges has been complex. Precast piles have been driven to depths of 20m into load bearing strata, and all bridge decks are post-tensioned. As far as possible, materials are sourced from Abu Dhabi or, if this is not practicable within the Emirates or the Gulf area.

The specification of the road is first class. It is lit along its length and is equipped with box girder safety barriers. The bridges have a 6.5m clearance and are equipped with electronic warning systems to alert high- sided vehicles. There is comprehensive signing in Arabic and English. The Arabic signs have caused something of a headache however, since there are alternative spellings for a number of the destinations. Signs on overhead gantries are illuminated to be clearly read at night.

Something that must have struck every traveller along the old route was the sudden swathe of greenery at the approach to Abu Dhabi city. Such is the value of trees in this desert kingdom that it was enough to require a change in the alignment on Contract 2. The final touch for the upgraded road will be the planting of several million trees turning the route into a green lane.

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