Well it seems that with the construction of the Hitchin-to-Cambridge flyover attached to the Thameslink programme is to be taken in hand relatively soon (assuming work hasn't already started), there is only one major bottleneck remaining on the Southern ECML, that being the two track section surrounding the Welwyn Viaduct and its attached tunnels. As far as I can see this will have to be dealt with sooner or later as it must be putting a damper on the suburban and intercity timetables. The options as far as I can tell are: 1) Leave as it is and either invest in diverting additional freight and passenger trains via the Hertford loop to free up paths or simply put up with the restriction 2a) Construct a new pair of two-track tunnel bores to quadrouple the line north of Welwyn North station, rebuilding the station completely to allow the four track section to extend all the way to the North end of the bridge, reworking the track at the south end to enable all four tracks to reach the South end, shortening the twin track section by more than half and removing the station from it. 2b) Construct a new viaduct immediately to the east of the current one, probably with strengthening of the original bridge's foundations and placing the new supports so that the original view down the valley is preserved to the greatest possible extent. 3) Construct a twin-track tunnel from the northern end of the Northernmost Welwyn tunnel to somewhere immediately north of Welwyn Garden City station, allowing it to carry the fast tracks under the valley, this is the most expensive option but would completely remove the bottleneck with minimum disruption to the visual environment surrounding the existing Viaduct, it would however have to be rather steeply graded to reduce its length and cost and thus freight trains would be unable to use the fast line during engineering works. I myself support either option 2a or 2b (if unlimited money was available) however I fear we will get nothing happening whatsoever.