The northern section of the line passed to the North British Railway company (NBR) and became part of its suburban network.

In the 1960s, rationalisation of railway facilities was the theme, and all the south-facing passenger services were concentrated at Glasgow Central station.

The through route remained open for occasional freight services and for empty passenger stock movements across the city.

Suggestions had been made for some years to connect the lines south and north of the Clyde: in 1846 a parliamentary select committee produced a report of 1,470 pages on the subject, but in the face of opposition from vested interests including those who received the tolls on the existing road bridges, nothing was done.

The promoters were contractors, hoping to generate construction work for themselves, and they wished to involve all the railways in the scheme, taking a substantial block of shares themselves.

[note 1] The G&SWR and the Edinburgh and Glasgow Railway (E&GR) were favourable towards such a scheme as the trade in goods between their areas of influence was considerable, and the available through route was circuitous.

[1][2][3] The line would be over 6 miles (9.7 km) long, from West Street to Sighthill, where the E&GR had a goods yard; it would cost £650,000 to build.

There is no indication where the tracks are destined; in earlier years there had been considerable interest in providing rail access to the Broomielaw quays on the north bank of the Clyde, and this may be the purpose.

[6] The capital requirement soon escalated to £900,000, and the G&SWR and the E&GR were supportive, but the CR was not greatly interested (and may have taken offence at the manner of the approach) and opposed the scheme.

In early 1865 it was agreed that the G&SWR and the E&GR would between them take the whole of the stock of the new company, releasing the prospective contractors from that obligation.

The scheme for the general passenger station was now modified, as it emerged that the NBR did not contemplate making much use of it, although hopes lingered that the Caledonian would have a change of heart and join in the project.

The new line incorporated the first railway bridge over the Clyde in the city; but the St Enoch Square terminus had not been started yet.

Trains towards Bellgrove worked into Dunlop Street terminus, and then were propelled back to Clyde Junction to resume their onward journey.

At this time the NBR was extending westwards from Coatbridge via Shettleston and opened the line to College passenger station on 1 February 1871.

[8] Negotiations between the G&SWR and the English Midland Railway for mutual co-operation or merger had blown hot and cold.

The station was the first public area in Scotland to be lit by electricity, although 464 gas jet lamps were provided as an emergency standby.

[4] As late as July 1876 the Caledonian Railway renewed an approach concerning use of St Enoch by their trains; they were rebuffed by the G&SWR, who said that a minimum payment of £500,000 would be necessary to permit the access.

The section east of College West Junction fell logically to the North British, and it was proposed to divide the company, the NBR taking 40% of the share capital.

The through route from Shields Junction to Bellgrove remained in use for a light freight service, and to transfer empty coaching stock across the city.

The large span lattice girder bridges over Saltmarket, London Road and Gallowgate, and the elevated viaduct sections there and near Cumberland Street are reminders of an ambitious scheme to connect the north and south railway networks in the city.

After a short section in which CGUR trains used the NBR line, the CGUR reappears, swinging northwards at the east end of Bellgrove and climbing in retaining-wall cutting to Alexandra Parade and then in more open country crossing the original Garnkirk and Glasgow Railway line to Barnhill and Sighthill Junction.

It consisted of twin-lattice parallel iron girders in seven spans; the engineers were John Fowler and J. F. Blair, and the contractor was Thomas Brassey & Co..

In 1898 the bridge was reconstructed and widened for quadruple track; compressed air excavation for 13-foot (4.0 m) diameter steel piers were used.