Too many rumours.
I've heard more than a couple of rumours, none of which overlap with the replies you've already had.
1) Adding a pantograph trailer would render the entire unit a "new" train and, therefore, subject to all the current legislations regarding diesel emissions and electronic systems compliance, all of which the units would fail.
2) There are no transformers small enough to fit underneath the floor that are man enough to provide both traction and "hotel" power for the entire train. To get around this, the diesel engines would be required to run to provide at least some of the electrical power required by the units thereby negating the proposed benefits of adding the capability of running off the OHLE.
3) The only transformers available that might even get close to providing the capabilities required are manufactured in the Ukraine and contain all manner of materials unpalatable to the Western world. Suffice to say, any such components would contravene the laws of the EU and it's member states.
Before I get shot down I should like to stress that these are simply the rumours that I have heard to help explain the reason why the project has been kicked into the long grass. My own belief is that these are simply excuses to cover for the real explanation, which is that constructing pantograph trailers and integrating them into the existing formations is simply too hard and, therefore, too expensive.
I see no reason to expect that XC will have any more HST sets cascaded to them to increase capacity. Probably the only hope is that somehow Virgin WC can be induced to give up their Voyagers. However, perhaps the Trans-Pennine electrification will trigger a Cl170 cascade to benefit XC which may, by some roundabout way, result in the pressure being eased on the Voyager fleet.
But then the real problem is not with the units themselves. Since the Voyager fleet was introduced the XC network has seen an upswing in demand. Given that the days of fleet flexibility and hiring in stock to cover increases in demand have gone, XC have been placed over a barrel. Given that XC (and, by extension, all other TOCs) have finite and limited rolling stock at their disposal, what more can they be expected to do. Intercity TOCs aside, XC is particularly exposed to these vagaries and particularly vulnerable to variations in loading given that their formations generally only vary by a vehicle or two depending on allocations. Taking platform lengths on certain routes into account together with the fact that upswings in demand are not localised on specific locations within their operating area, XC are in a hole with few options of escape. Adding a coach or two to existing formations may help to ease some services but wouldn't herald an overall improvement in service provision.
Therefore I don't believe that there is much that these projects could realistically achieve.
O L Leigh
