Despite Boris's latest noises, I don't think Crossrail 2 is going to happen. And Yet HS2 looks like it will, and will dump loads of extra people into Euston, with nowhere to go.
It is said that London Underground's Northern Line cannot be split into two lines without a major rebuilding of Camden Town station, because of the large number of people who would need to change trains there. However, such a rebuilding would be a wasted expense in the long term, because people change their place of residence on average every seven years, and I think change their place of work even more frequently. As soon as the lines were split, any people changing residence or job would plan their new commute around the new tube map, and so after a decade, the vast majority of current Northern Line commuters would either work and live on the Bank Line or work and live on the Charing Cross Line, and the glut of people changing at Camden Town would have been a short lived phenomenon.
There is a nearly free solution. Declare the line to be two separate lines - a Bank Line to Barnet with a "limited" service to Edgware, and a Charing Cross Line to Edgware with a "limited" service to Barnet. The map would give each routes south of Camden its own colour, and each line north of Camden would be a double stripe with one of the colours dashed (as used to happen between Rayners Lane and Uxbridge when the Piccadilly Line had a limited service supplementing the main service of Metropolitan Line trains). The timetables would not change, still providing 50% service to each branch from each trunk, so there would be no overcrowding at Camden. The stigma of limited service shown on the map would affect people's perceptions, and anyone changing residence or job would avoid planning their commute around the supposedly limited service, and thus journey patterns would gradually to shift to match the map. After three years you bring in a new timetable with 60% following the main routes and 40% following the limited routes. The gradual shift of journey patterns continues, so every three years you can switch to 66% main and 33% limited, then 75% main and 25% limited, then 80% main and 20% limited, and finally fifteen years after splitting the lines on the map you can split the lines completely, without ever overloading Camden or rebuilding it.
Since the consecutive trains following each other on the main routes could be closer together than the trains going in different directions, the frequency could gradually increase as the proportion of following pairs increased, until the final separate lines could run significantly higher frequencies than at present at both of the platform pairs at Euston, significantly increasing the ability to absorb the passengers from HS2, without having used one shovel.
It is said that London Underground's Northern Line cannot be split into two lines without a major rebuilding of Camden Town station, because of the large number of people who would need to change trains there. However, such a rebuilding would be a wasted expense in the long term, because people change their place of residence on average every seven years, and I think change their place of work even more frequently. As soon as the lines were split, any people changing residence or job would plan their new commute around the new tube map, and so after a decade, the vast majority of current Northern Line commuters would either work and live on the Bank Line or work and live on the Charing Cross Line, and the glut of people changing at Camden Town would have been a short lived phenomenon.
There is a nearly free solution. Declare the line to be two separate lines - a Bank Line to Barnet with a "limited" service to Edgware, and a Charing Cross Line to Edgware with a "limited" service to Barnet. The map would give each routes south of Camden its own colour, and each line north of Camden would be a double stripe with one of the colours dashed (as used to happen between Rayners Lane and Uxbridge when the Piccadilly Line had a limited service supplementing the main service of Metropolitan Line trains). The timetables would not change, still providing 50% service to each branch from each trunk, so there would be no overcrowding at Camden. The stigma of limited service shown on the map would affect people's perceptions, and anyone changing residence or job would avoid planning their commute around the supposedly limited service, and thus journey patterns would gradually to shift to match the map. After three years you bring in a new timetable with 60% following the main routes and 40% following the limited routes. The gradual shift of journey patterns continues, so every three years you can switch to 66% main and 33% limited, then 75% main and 25% limited, then 80% main and 20% limited, and finally fifteen years after splitting the lines on the map you can split the lines completely, without ever overloading Camden or rebuilding it.
Since the consecutive trains following each other on the main routes could be closer together than the trains going in different directions, the frequency could gradually increase as the proportion of following pairs increased, until the final separate lines could run significantly higher frequencies than at present at both of the platform pairs at Euston, significantly increasing the ability to absorb the passengers from HS2, without having used one shovel.