Capacity was one of the key issues for critics of HS2 when the Commons Transport Select Commitee [TSC] held hearings during the summer of 2011. The realistic capacity of the proposed high-speed railway connecting northern England, the West Midlands and London is critical to its operational credibility and hence to its business case. PTN was among those who worked to put the issue on TSC's agenda. The matter is still far from being resolved.
The nub of the problem is that expectations of what HS2 can do for connectivity have been so enthusiastically promoted that some 25 to 30 paths/hour could be 'needed'. HS2 Ltd believe that running 18 trains/hour is feasible, although that is several more than any other high-speed line has achieved. Given this gap, and the possibility of 16 trains/hour being the everyday maximum, some difficult choices will have to be made, and since they may affect major decisions such as the link to HS1 they need to be made soon.
The TSC's Report is at : http://www.publications.parliament.uk/pa/cm201012/cmselect/cmtran/1185/118502.htm#evidence.
See paragraphs 112 - 117 for the discussion of technical feasibility. For PTN's submissions see the Unprinted Written Evidence, HSR 138 and 138A and for the exchange relating to the latter see the transcript of oral evidence for 28 June, Question 126 (the links are at the foot of the page).