page_title: Portway, Bristol
section_title: Construction
hierarchical_section_title: Portway, Bristol / Construction
caption_attribution_description: English: Road bridge and footbridge across the River Trym, Sea Mills, Bristol
context_page_description: The Portway is a major road in the City of Bristol. It is part of the A4 and connects Bristol City Centre to the Avonmouth Docks and the M5 motorway via the Avon Gorge.
  The road was constructed following World War I in order to provide improved access to the ports at Avonmouth Docks, which had replaced Bristol Harbour as the major local centre for commercial shipping. Upon opening on 2 July 1926, it was the single most expensive road project in Britain, costing £800,000. The construction posed a number of significant engineering challenges, including long and deep rock cuttings, a viaduct over the River Trym, and retaining walls against the gorge adjacent to the River Avon. Falling rocks have since been a problem along the Portway, particularly at the southern end close to the Clifton Suspension Bridge, with concrete canopies constructed to prevent loose rock and assist with remedial work.
  The Portway remains an important route to and from Bristol, and is now used as part of the Portway Park and Ride scheme.
context_section_description: The Portway was planned by the Bristol Corporation in response to the decline of Bristol Harbour in the late 19th century in favour of Avonmouth Docks, which could handle larger vessels and containers. Construction started in May 1919, engineered by L. S. McKenzie. The southern section connected to the existing road network at Hotwells, and a portion of the new road near Clifton lay partly on the line of the Bristol Port Railway. The new build did not directly connect to Avonmouth Docks, but linked to the existing road via Shirehampton about half a mile from the dock gates. The original plan was to build a tramway along the length of the road, which would have linked Avonmouth to the Bristol Tramway system, but this was abandoned owing to cost.
  The largest cutting on the construction was at Horseshoe Bend. It was 2,400 feet (730 m) long and cut 90 feet (27 m) into the rock at its deepest point. Upstream from this, a viaduct was needed to span the River Trym and the remains of a Roman harbour. It was composed of six 42-foot, 6-inch (12.95 m) arches, with abutments embedded in the rock 14 feet (4.3 m) below. It was supported by three piers at 17 feet (5.2 m), 21 feet (6.4 m) and 40 feet (12 m) below road level. Construction of the viaduct was delayed owing to the tidal flow of the River Avon and the irregularity of the rock. A skew girder bridge was constructed to cross the Severn Beach Railway near Sea Mills station, with foundations up to 55 feet (17 m) below the surface. Around 3,000 feet (910 m) of retaining wall was required at the Bristol end, where the road was sandwiched between the River Avon and the side of the gorge. In September 1924, approximately 200 yards (180 m) of newly constructed concrete embankment slid into the river following ground subsidence, posing a hazard to navigation and adding 12 months to the duration of the work, though there were no injuries.
  The Portway was opened by the Minister of Transport, Colonel Wilfrid Ashley with the Lord Mayor of Bristol, Alderman Moore, on 2 July 1926. Following an opening ceremony, the Minister and Lord Mayor drove along the full extent of the road from Bristol to inspect the docks at Avonmouth. It was the most expensive road construction project in Britain, costing £800,000 (now £46,776,000). Of that, £160,000 (now £9,355,000) was spent on the cutting at Horsehoe Bend, £80,000 (now £4,678,000) on the Trym viaduct, and £33,000 (now £1,929,000) on the steel girder bridge.
  Electric lighting was provided to illuminate the new road, but for one year after the opening the lights were kept switched off following objections from river pilots who argued that they would make it hard to distinguish the navigation lights of shipping and the signal lights on the shore. Eventually the electric lights were turned on at a reduced brilliance.
  The Portway was numbered A36 when first opened. It was renumbered as a western extension of the A4 by the Ministry of Transport on 1 April 1935.
caption: The Portway crosses the River Trym on a six-arch viaduct near Sea Mills.
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