British Rail Midland Region London Rugby Line Bridge Number 115 (Folly Bridge)

Folly Bridge, also known as Bridge Number 115, is a road bridge over the railway at Tring Cutting, located partly in Marsworth Parish, Buckinghamshire. It was built around 1837 by Robert Stephenson for the London and Birmingham Railway Company. The bridge is constructed of brown brick and features stone impost bands, skewbacks, a cornice, and parapet copings. The northern parapet has been rebuilt for safety reasons using red brick with triangular section concrete copings.

This long, narrow bridge has three arches, with traffic controlled by lights on the B488 road, which crosses the deep Tring Cutting, approximately 50 feet deep and 2½ miles long. The central arch is a higher 7-ring segmental arch that spans the trackbed, supported by slender rectangular piers at the foot of the earth slopes on either side. Each pier has a tall opening with a round arched head and bottom. The side arches are slightly lower segmental 7-ring arches that are set into the earth slopes at the abutments.

At roadway level, there is a wide unmoulded stone cornice, a brick parapet, and rectangular terminal piers with weathered stone copings remaining on the south side. The cutting was created due to Stephenson's decision to maintain a maximum gradient of 1/330 on the line, and there is a well-known lithograph by J.C. Bourne depicting the excavation work by navvies. The railway line was officially opened on April 9, 1838, and the county boundary with Buckinghamshire runs along the centerline of the road over the bridge.