Underground Extension To Streatham
Back in the late 1980s, plans were seriously looked at which could have seen a new Northern Line spur constructed between Kennington, and either Streatham, or along the proposed Bakerloo Line extension, towards Peckham.
Obviously, it never took place, but the plans for Crossrail 2 had indirectly resurrected the proposals, although this time as a possible extension of the Victoria Line instead.
The 1988 “strategic review” noted that the ground conditions in much of South London are poor for tunnelling, composing mainly of sand and gravel. In many areas, the new tunnels would pass below the water table, requiring compressed air, or a slurry shield for the tunnel boring machine to function.
Another report into the Bakerloo Line extension showed that for the possible extension down to Streatham, it would be water logged soil only as far as Brixton, after which the conditions for tunneling improved markedly.
Regardless of where the line would go, there was the question of turning around trains fast enough to meet a 30 trains-per-hour requirement, and there could either have been a loop, as at Kennington and Heathrow, or the construction of three platforms instead of the usual two.
If the loop were to have been adopted, a spur would have allowed for faulty trains to be stored off the line, and a novel idea of including a maintenance pit in the siding itself could have assisted with faster repairs.
The Streatham route follows the A23, running deep to pass beneath sewers and the Victoria Line at Brixton. There are four new stations on this line, at Brixton – interchange with Victoria. Line, Brixton Hill, Streatham Hill – interchange with BR services to West Croydon, and Streatham – interchange with BR services to Sutton. There is a terminating loop at Streatham. After Brixton, there is a sustained 1 in 50 gradient to Brixton Hill, but as the gradient of the street above is similar, the line remains at about 30 metres below ground level. It should be noted that there are gradients of similar slope and length on the Hampstead Line, so this one will not be a limiting factor on the line, even though it is more severe than is normally recommended. Beyond Brixton Hill, the line can be built on the hump station profile. Most of the alignment can be kept under streets, without introducing sharp curves, except between Streatham Hill and Streatham, near stations and around the terminal loop where it passes under houses.
None of the stations were described in any detail, although it was presumed that apart from the physical need to get down to the tunnels, most of the station building would reuse the existing British Rail station facilities.
The exception would have been either of the proposed Camberwell Green or Brixton Hill stations. Camberwell Green being a sub-surface station, tied in with a series of proposed subways under the local road junction.
The whole project, would have come to £264 million for the link to Streatham. Those costs excluded the need for additional trains, and a presumption that soil conditions didn’t prove to be worse than expected.
While the link to Streatham is dead as far as the Northern Line is concerned, a report into Crossrail 2 noted that CR2 could relieve congestion on the Victoria Line to the level needed to support that line being extended down to Streatham. The line already extends past Brixton a decent enough distance in anticipation of a future extension.
And finally, following the recent consultation on the Bakerloo Line Extension, TfL is currently reviewing the case for the proposed extensions, including different route options and possible station locations across south London.