At Prestwich, in north Manchester, motorway, bridge and railway line pass one above the other in 'asterisk' formation. A concrete railway bridge was constructed directly above the road bridge, which itself passes above the M60, formerly M62 motorway.

See this location from above in Google Maps.

The railway bridge is of a very unusual design. Read the technical description below, submitted by John A Smith, who was involved in the construction.

In 1966, British Rail Midland Region commissioned Trevor Crocker and Partners to carry out the detailed design of the above bridge.

The bridge over-spans the Manchester to Radcliffe main road which, in turn over-spans the M62 Cross Pennine motorway.

The railway bridge is of three spans, the main (central) one being 250 ft long. The bridge is constructed entirely of pre-stressed concrete and consists a central hollow spine box beam, 22 foot deep with cantilever wings either side to support the rail tracks.

The bridge is constructed in an area of anticipated high subsidence due to mining activity and great care was taken in the design to mitigate the effects of possible gross ground movements, large jacking capability being built in.

Each span is supported at three points only to ensure all bearings are constantly supporting the bridge irrespective of any subsidence which may take place (the milkmaid stool effect). Transition of the cantilevered decks between each span is via large triangular transition decks, again supported on three points only.

Span 1 is supported on a single bearing at the abutment and two bearings at the first intermediate support, which it over-spans. Span 2 (the main span) is supported by a single bearing on the stepped end of span 1 and two further bearings at the second intermediate support which it too over-spans. Span 3 (the shortest span) is again supported by a single bearing on the stepped end of span 2 and two bearings at the abutment.

The spans of the cantilevered wings on span 3 are increased to enable tracks to separate at the approach to Besses O 'th Barn station island platform.

Longitudinal pre-stressing utilises the "Freyssinet" system whilst vertical web and transverse deck stressing is achieved using McCalls "Macalloy" tensioned threaded bar stressing system.

Two one twelfth scale models of a box beam stepped beam end were constructed at BR Derby Laboratories to prove the design and ensure the complex reinforcement could be fixed. Both models were tested to destruction.

Overall design was conceived by British Rail Midland Region whilst detailed design was undertaken by Trevor Crocker and Partners.

Many thanks to John A Smith for this authoritative description of a bridge which may not be the most beautiful in the world, but it is certainly technologically sophisticated and meets the unique demands of the location

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Keywords: Manchester motorway bridges, M60 book, M62 motorway construction, Prestwich, Bury MBC, motorways, Lancashire highways, bridges, Lancashire