It opened as a broad gauge (7 ft 1⁄4 in [2,140 mm]) line to connect new docks at Portbury, at the west side of the mouth of the River Avon, with the railway network.

When a new high capacity freight terminal was opened at the site of the Royal Portbury Dock, the line as far as that point was reopened to accommodate the new traffic, in 2002.

However the city centre location, and the difficult tidal negotiation of the Avon valley, was increasingly a constraint on development, particularly as larger vessels came into use.

c. cccxliv) to build a floating pier near Portbury, on the west side of the Avon near its mouth, and a railway to connect it to Bristol.

At this time the collapse of investor confidence following the period of railway mania was taking effect, therefore finance for the work could not be raised and the new company was dissolved.

[3][page needed] In 1849 a small stone pier was built at Portishead, and packet steamers unloaded passengers there from that time; but this did little to reduce the desire to improve the city's port facilities, and competing factions tried to get approval for their schemes.

The main line would have curved sharply to the north before reaching Portished, and run directly to a northwards pier on the coast somewhat east of the present Portbury Wharf location.

Work progressed swiftly, and a portion may[note 1] have been opened in early 1865 from Rownham near Clifton Bridge to the junction with the B&ER main line near the Telegraph Inn in Bedminster.

He noted that the gradients and curves were significantly inferior to those on the original 1863 design; this probably indicates that they were sacrificed to reduce earthworks and avoid one of the tunnels.

However Yolland found numerous shortcomings; as well as fencing deficiencies there were inadequate clearances to two bridge abutments and to retaining walls, and in the No.

[4] The emphasis now was on passenger and ordinary goods traffic, and the original objective, the shipping facility, was on the back burner; reporting the opening, the Bristol Times said, "It is intended shortly to commence a port, which is expected to occupy about two years in the erection.

During 2000 and 2001 the railway was rebuilt as far as Pill, and a short spur constructed to the Royal Portbury Dock to carry freight.

The alignment is breached on the southern approach to Portishead by Quays Avenue, constructed to serve housing development around the former dockside.

[14] During the Rail Priority Conference organised by the West of England Partnership in November 2011, delegates travelled on the line, using sections of track not open for passenger traffic.

[17] This will use both existing and disused rail lines in the Bristol area, operating half-hourly services subject to a proven business case being made and infrastructure constraints.

[21] In March 2017, MetroWest reported a substantial increase in the estimated costs of Phase 1, owing to the work required to upgrade the line in the Avon Gorge to achieve the line speeds required for a half-hourly service, and to reroute road traffic away from a level crossing in Ashton Vale.

[22] In order to reduce the cost from an estimated £145 million to £116M, the Joint Transport Board agreed to downsize the project to provide an hourly service to Portishead.

[25] The Department for Transport's Rail Network Enhancements Pipeline, published in October 2019, listed the project among those in development, awaiting a "Decision to Deliver" and the completion of a full business case.

[26] In November 2019, North Somerset Council submitted a Development Consent Order (DCO) application to the Planning Inspectorate, which sought powers to build and operate the disused section of railway from Portishead to Pill, gain environmental consent to undertake works to the existing freight railway through the Avon Gorge, and obtain powers for the compulsory acquisition of land.

Subject to final business case approval, construction work had been expected to start in April/May 2022 and take around two years to complete.

[30] It was reported in November 2022 that construction work to reopen the line to Portishead for passengers would not start until 2024, and the earliest opening date would not be before 2026.

[31] In December 2023, it was announced that a business case would be submitted the following year and construction could start before the end of 2024 with an anticipated opening date of 2028.