[3][4] At the early date when the design of the line was being finalised, Brunel was not confident of the ability of the steam engines of the day to ascend significant gradients pulling a load, and the solution appeared to be to concentrate the stiffest climb in a limited distance, and to make the remainder of the route as near to constantly level as possible.

The short, steep sections could, he believed, be worked with stationary steam engines hauling the trains up by rope.

Now that the Severn Tunnel was available, that traffic could run via Bristol (or the short avoiding line known as Dr Days Curve) and Bath.

The Barry Railway Company had been exceptionally successful in South Wales in building ambitious and well-laid-out lines to its modern and well-equipped port.

It was to build a new line from Cogan via Cardiff and skirting Newport on the north side, crossing the River Severn at Beachley by a new 3,300 yard bridge, then via Thornbury, Malmesbury and Lechlade, to make a junction with the Metropolitan Railway near Great Missenden.

[13][14] For at least a decade, the Great Western Railway had indicated that it might build a cut-off line to shorten the route from the Severn Tunnel to London, but it had not done so.

The contractor used a remarkable number of steam locomotives in the work: 50 were in use at one time or another (but not simultaneously), reflecting the volume of earth that was moved.

[3] On 26 June 1903 Colonel H. A. Yorke of the Board of Trade made an inspection of the line over two days; BoT approval was a requirement before the operation of passenger trains was permitted.

[4][2] A large marshalling yard was built at Stoke Gifford, with ten sidings capable of holding 500 wagons.

[18] From 1832 a horse-operated tramway, part of the Bristol and Gloucestershire Railway, was constructed to connect coal pits in the vicinity of Coalpit Heath with the River Avon near Keynsham.

The GWR wished to use the loops to operate an independent service between Bristol and Gloucester, using running powers over the Midland Railway.

However the Midland argued that the running powers, so far as the Westerleigh and Yate connections were concerned, only applied to traffic for the Severn and Wye line.

This included the provision of a new Westerleigh East Junction signal box; the curve was available from 16 August 1942 until final closure on 4 January 1950.

[19] The Malmesbury branch had opened on 17 December 1877, running from Dauntsey station on the Great Western Railway main line.

There was no passenger station there, and the slipped vehicles were taken on to Temple Meads by a train specially run to Stoke Gifford for the purpose.

[3][20] In Table 10, Fryer shows one slip at Stoke Gifford in 1932 for Bristol Temple Meads; and two in 1938, one of which continued to Taunton and the other to Weston-super-Mare.

[20] To mark the centenary of the Great Western Railway, the company inaugurated an express train named The Bristolian in 1935.

[21] The area served by the line was sparsely populated, and after World War II patronage of the intermediate stations fell away.

Very few through passenger trains used the former GWR alternative, through Filton and Westerleigh, except during busy periods at summer weekends.

As an out-of-town location, it would be attractive to motorists in the Greater Bristol area, who might drive to the station and park, continuing by rail.

In addition to the track formation work, crossovers for reversible operation were installed, and special arrangements were made for the permanent way staff's refuges in Alderton and Chipping Sodbury tunnels.

This included handrails "to prevent [the track workers] being drawn out of the recess by the turbulence caused by a passing High Speed Train".

[note 9][23][24] From Wootton Bassett Junction the line fell generally at 1 in 300 to Little Somerford, then climbing at the same gradient to Badminton.