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A40(M) Westway and M41 West Cross Route



NOTE:
Following the formation of Transport for London (TfL), these roads were reclassified in May 2000. This change was required because the Greater London Authority (GLA) Act does not give the Mayor for London powers to be the highway authority for motorways, but these roads were being transferred to the Mayor. It was therefore necessary to remove their motorway status before June 2000 when the Mayor took office. Westway is now simply a section of A40, and the West Cross Route is a section of A3220.

These were two of the four independent sections of urban motorway in London, all built by the Greater London Council (GLC) during the period 1967 to 1973, funded by the Council with 25% government grant.

These schemes were built under Parliamentary Powers in a bill promoted by the LCC on 29 October 1962. The bill included other disparate proposals for capital projects and was subject to scrutiny by a committee in the Lords presided over by Lord Goddard. There was no public debate, officers gave evidence and in general, line, intent and land take were granted to the proposer. G Maunsell and Partners were appointed by the LCC as Engineer for these schemes.

Western Avenue Extension (named Westway - A40(M)) is an elevated motorway 4km long, connecting the end of the existing Western Avenue (A40) at Wood Lane, adjacent to the White City Stadium, to the Marylebone Flyover at Paddington Green, and hence gives access to the Marylebone Road. It thus provides a direct link into Central London from the west.

At the west end, the first length of the West Cross Route (M41) was constructed. This is a ground level motorway, 1km long, and runs from the interchange with Westway southwards to a ground level interchange with the existing road system at Holland Park Avenue adjacent to Shepherds Bush.

Westway and M41 West Cross RouteTheir intersection is an elevated roundabout at White City, accommodating movements in all directions, with a flyover for through Westway traffic. Spurs off the North side of the roundabout were constructed for the possible northward continuation of the West Cross Route. They are still present and one can be seen on this picture.

At the Paddington end, at ground level there was a major realignment of the Harrow Road into a dual carriageway complex, the eastbound carriageway maintained a route generally to the north of the structure, whilst the westbound carriageway started as an elevated road at intermediate level under the structure before passing in an underpass under Westbourne Terrace and joining the existing road. In this area there was also a partial interchange providing access to and from the west.

Design considerations divided the project naturally into six sections. Brief details of these are given below, which start at the western end of the scheme:

Section

Brief description

Westway A40(M)

Section l:
From existing A40 to St Mark's Road.
1190m long.

Comprised elevated roundabout, with slip roads and flyover. Included reconstruction of Wood Lane with a skew bridge over Central Line of London Transport, garaging and car parking facilities beneath structures, and a subway. Also pair of two-span slip roads west of Wood Lane. Included extensive landscaping beneath and adjacent to the superstructures

Section 4:
St Mark's Rd to Acklam Rd.
670m long.

Included service road from St Mark's Rd to Ladbroke Grove, and landscaping treatment.

Section 5:
Acklam Rd to near Torquay St.
3800 ft long.

Included crossing of mainline and other tracks of Western Region at Westbourne Park Station, reinstatement of railway land below superstructure and landscaping treatment of other areas.

Section 6:
Torquay St to Paddington Green.
975m long.

Slip roads at Ranelagh and Westbourne Terrace bridges provided ground level connections, near to the Royal Oak Station. Included new east and westbound Harrow roads, the latter passing through an underpass, also double roundabout system and three subways. Part of this road system lies over British Railway's goods and maintenance facilities. Included landscaping treatment beneath and adjacent to superstructure, and alongside the canal.

West Cross Route M41

Section 2:
From slip roads from elevated roundabout southwards at ground level to slip roads north of new ground level roundabout at Holland Park Avenue.
1005m long.

Dual 11m carriageways with 2.4m hard shoulders of Rigid pavement construction. New two-span bridge carried Metropolitan Line over route designed and constructed in advance by London Transport.

Section 3:
Diamond shaped roundabout linking West Cross Route with Holland Park Avenue, Holland Rd, Uxbridge Rd and Shepherds Bush

Included two bridges over West London line of British Railways, four subways and footbridge with passenger conveyors at Shepherds Bush. Substantial diversion of services required.
New shaft and tunnel was driven under compressed air to replace existing shaft within the roundabout, ventilating the Central Line of London Transport.

 

The elevated route is primarily of prestressed concrete construction, and a significant feature is section 5 with a curved section of about a kilometre built in continuous spine beam form over the main railway line from Paddington, requiring large steel comb bridge joints at its ends. The architects William Holford and Partners advised Maunsells on appearance.

Westway and M41 West Cross Route2The Harrow Road Flyover is incorporated in the motorway at the east end where it joins the Marylebone Road. Sir Bruce White and Partners were Engineer for the flyover, with Cementation as contractor. As the consent to build the flyover under Parliamentary Powers, which pre-dated Westway, were for the purpose of improving the movement of local traffic crossing the Harrow Road there is no exit for motorway traffic just prior to it, only eastbound access; there is a similar arrangement on the west side of the flyover for the exit of Marylebone traffic with no access to the motorway there.

At the western end, the horizontal alignment was determined by the existing Westway and the close proximity of the White City Stadium. Eastwards the route lay alongside the London Transport Metropolitan Line, and then across the main lines and sidings of Western Region of British Railways at Westbourne Park Station. Thence it lay immediately to the north of the railway tracks, finally passing through Paddington Goods Depot and crossing the Grand Union Canal. The alignment at the eastern end was determined by the existing flyover crossing Edgware Road.

The following basic alignment criteria were adopted:

Minimum radius for main route: 460m
Design speed for main route: 50 mile/h
Operating speed limit: 60 mile/h
Design speed for slip roads: 30 mile/h

Controlling points for the vertical alignment were clearances over:

  1. Wood Lane, with slip roads to and from the elevated roundabout at Westway;
  2. Central Line of London Transport;
  3. West London Line of British Railways on embankment, with allowance for future electrification; and
  4. all local roads and the new Westbound Harrow Road which spans the Grand Union Canal.

Longitudinal profiles had a minimum gradient of 1 in 200. Maximum gradients were1 in 25 on main ramps and 1 in 20 on slip roads. For the underpass at Westbourne Terrace Bridge, gradients are 1 in 15 down and 1 in 18 up.

The routing of the highway through railway property required considerable alterations to existing buildings and provision of a new maintenance depot at Paddington. Reconstruction of a timber yard and canal weir chamber at Paddington was also necessary.

Elevated highways, even when sited alongside or over railways, require demolition of property and could be a further divider of neighbourhoods. There was no power or duty at that time to compensate people living outside the highway limits for any adverse effects of a scheme - this was not available until 1973.

All structures were required to carry HA loading and also 45 units of HB loading in any position, including hard shoulders. Horizontal curves require that lateral restraint forces have to be transferred from deck to ground and superelevation is reflected on the soffits of superstructures of constant depth.

Expansion joints in carriageways detract from smooth riding qualities, are expensive to fabricate, troublesome to install and require maintenance. Joints between superstructures of different types were located at abutments where internal drainage could be incorporated. Consequently, joints were avoided, except when they could be provided without interruption of the surfacing.

The scheme was planned to be dual 3-lanes, and was so defined in the Parliamentary bill. In 1966 the director of highways and transportation visited the United States where he became convinced of the need for hard shoulders. The Highways and Finance Committees agreed to their inclusion, and as the shoulders could be accommodated within the enacted highway limits there was no need to return to Parliament. The Ministry of Transport also agreed to the change for grant, a sine qua non as far as the Council was concerned, and the design was changed accordingly. The effect on the advanced structural design was significant and the consultant's terms of engagement were changed appropriately. In the event, hard shoulders were added where lateral clearances permitted, and this change was made during the tender stage.

The following basic design decisions on structures were made:

Span lengths were assessed for the individual sections to take account of local conditions. These varied from 15m in section 4, where the motorway was of constant width and generally parallel to ground level, to 62m with a central column in section 5, where the motorway is at varying heights above ground, railway tracks and canal.

The whole of the alignment rests on firm to very stiff London clay which is found at or near ground level at the eastern end and is elsewhere overlain by variable superficial deposits. The lower limits of laboratory results were adopted for design of the cylinders with enlarged bases which were shown to be the most economic foundation method. A shaft diameter of 3 ft 6 in. was generally adopted and bases were enlarged to 10 ft 6 in. diameter. With these diameters the depths were varied to carry working loads between 380 and 450 tons. A number of 4 ft diameter cylinders were also used to carry loads up to 600 tons.

As work progressed, selected cylinders incorporated into foundations were subjected to proof load tests, all with satisfactory results.

Prestressed concrete superstructures were designed, generally to be erected by the span by span method. Precast concrete segments were used generally, but in areas of changing width and for the elevated roundabout, cast in situ construction was used. A family of torsion boxes of 5 ft nominal structural depth and of variable width with cantilevers on each side was evolved, the wider boxes having internal webs. To accommodate changes in superelevation, the overall central depth of the roundabout and eastern end of the flyover varied slightly. The slope of the outer splays on the soffits of the spine boxes is greater than the maximum superelevation of the deck to avoid intrusion into clearance heights.

The Elevated roundabout is unique in deploying a continuous spine box ring girder 400 ft in internal diameter, to which are attached the spine box girders of the slip roads. Cantilevering of part spans within the girder itself would have been structurally difficult at certain slip road junctions and also would have presented problems in the location of prestressing tendons. A simple predetermined span erection and stressing sequence was evolved which permitted structural analysis of the girder to be simplified and enabled structural cantilevers to be formed at slip road junctions ready for the later erection of the slip roads by the span by span method. The ring girder is of cellular form with internal webs and diaphragms over columns which was constructed in seven sequential concreting and prestressing stages, working in a clockwise direction.

All slip road superstructures, generally carrying two traffic lanes, consist of single cell box girders with cantilever slabs, post-tensioned longitudinally with a single bearing at each column. The box girders have the same uniform structural depth of 5 ft, the width of spine beam and cantilever slabs being varied to suit each carriageway. They were designed to be erected by the span by span method, except for the pair of two-span continuous bridges west of Wood Lane.

Westway and M41 West Cross Route3Precast concrete segments were used wherever possible for the Dual 36 ft and 41 ft wide carriageways, with in situ construction being required at the transition areas at the ends. Diaphragms and connecting deck slabs are of in situ concrete. Complete segments weigh up to 135 tons which is thought to be near the maximum economic lift. The novelty of the design required supporting research and development.

The Contractor demonstrated satisfactorily that whole units could be cast in two pours without shrinkage cracks. After transverse stressing the completed units were placed on storage beds ready for use.

A span of 168 ft was required at the canal. The structural depth was increased to 6 ft, and the extra foot of depth run out in the 100 ft span on each side, but the outer beams were kept at the normal depth throughout. It is virtually impossible to detect visually the increase in depth from 5 ft to 6 ft as the structure sweeps over the canal.

Westway and M41 West Cross Route4 The Westbound Harrow Rd crosses the canal immediately below the main canal span by means of a 107 ft simply supported hollow box beam bridge. West of this bridge the roadway continues below the main superstructure between the steel portal legs as a double-decked structure above railway facilities, carried by 50 ft span top-hat beams supported on reinforced concrete portal frames. Every other one of these also carries a steel portal frame.

The design of the concrete portals had to be integrated with that of the new maintenance depot, and construction proceeded concurrently under separate contracts prior to the commencement of the main work.

A single contract was let to Laings, and the works were inaugurated on 29 September 1966, with completion in July 1970. The works cost was £15.3M, adding land acquisition, preliminary and accommodation works the total cost of the scheme was £36.5M. The Prince of Wales visited the works in progress in 1968 when he was nineteen. This was his First visit to an industrial project as part of a programme of engineering visits drawn up by Prince Philip.

As decisions had not been taken at time of tendering regarding road heating, lighting, subway finishes and railings, suitable provisional sums were included in the Contract, and sub-contracts were placed accordingly. Agreements on signing, road markings, and traffic control were not reached until a very late stage, and these sub-contracts seriously affected the Contractor's programming in the months prior to the opening.

The scheme was designed to have dado lighting incorporated in a continuous rail mounted on the central concrete barrier. A trial section was built at Crystal Palace and tested for wet and dry surface conditions at night by police drivers, observed by Ministry officials and GLC officers. It was considered unsuitable, particularly because of patchy specular reflection when the road was wet. The design was changed to a conventional mast lighting scheme; a decision encouraged by the fact that the Ministry said that not even grant relative to the cost of a conventional scheme would be forthcoming if the dado scheme went ahead. On the architect's advice the rail on the central barrier was redesigned due to the removal of the lights.

Extensive alterations to services of the undertakers were necessary, and the design of permanent work was adjusted in various instances to accommodate pipes, mains and ducts in revised positions. The interrelation of the work carried out in consecutive steps by the undertakers themselves with the main Contract work proved extremely complex, and caused serious delays to the Contract.

All areas of land available for use below and adjacent to the super-structures were given careful consideration in conjunction with the Council and the Local Authorities to allocate them for present and future usages with the objective of improving the environment of local neighbourhoods, particularly in the dilapidated areas of North Kensington. Agreement was reached with the former Ministry of Transport that grant would be paid to the Council for basic landscape treatment, including generous tree planting on all land flanking the highway. Land to be used for future public open spaces by Local Authorities and land for commercial purposes would not attract grant.

A total area of 42,200 sq. yd of carriageways, including all ramps and the elevated roundabout, is heated by expanded metal mats embedded in the asphalt surfacing operating at 50 V. Local transformers are sited in pits in solid ramps and in cells of decks. Switchrooms, including automatic controls, for temporary works, formwork details and shop drawings from sub-contractors.

A police operated traffic control and surveillance system was incorporated in the works, and they had stated that they would not allow the road to be opened unless it was ready and tested. Pressure mounted when all the purpose made coaxial cable for the system was stolen from the contractor's compound, close to the planned opening date. There was no hope of it being replaced in time and there was relief when the cable was found and the thieves apprehended. This relief was dashed when the CID would not release the cable as it was required for evidence in court. Eventually, an Assistant Commissioner at Scotland Yard arranged with his colleagues that if they kept two feet of it the rest could be released. This event was indicative of the goodwill and co-operation that existed between all the interested parties without trespass on their respective duties

A crisis arose at the time of opening due to the proximity of the road to residents of Acklam Road where it ran very close to first floor windows; action to blockade the road was threatened unless the GLC took action. There was no power, or duty, to compensate and the Ministry refused financial help. The GLC found legal grounds for action and took a declared one-off step to purchase or soundproof the affected dwellings at the Council's cost, without prejudice to their continued urging for the government to introduce compensation outside highway limits. Subsequently a Council policy decision was made that no future major improvements would be built until such powers were available.

In the event, the tape cutting was only mildly interrupted by protesters who made their point and moved on at police request.

all superstructures including abutments were to be carried on large diameter foundation cylinders with under-reamed bases;

  • all drainage and services were to be concealed within superstructures, supporting columns and abutments;
  • repetitive methods of deck construction were to be employed;
  • superstructures would preferably be made continuous over numbers of spans ;
  • all superstructures, irrespective of type, were to be unified above deck level with similarly detailed safety barriers and lighting;
  • all superstructure decks were to be covered with a waterproof membrane over which hot-rolled base and wearing course asphalt would be laid.