As far as I know all the tram trains are fitted with the signalling systems they need, but only 4 at a time are supposed to have the 'railway' wheelsets. There is apparently a 5th set of spare 'railway' wheels, should they be needed. Which I guess they probably have been!
The wheel profiles are interesting because, as Lemmy said, a compromise profile was designed for the tram-train route vehicles. Apparently ordinary tram wheels can't run on Network Rail and ordinary train wheels can't run on the old Supertram network. I say 'old' because even the compromise wheels can't run on the grooved street track which existed on most of the system. However with the recent rail replacement work I would hope they've had enough foresight to change the rail so compromise wheelsets will eventually be able to work everywhere.
Are you confused yet? You will be...! Read on...
Now... two out of the 7 tram trains have been onvolved in fairly serious accidents, strangely both in almost the same place. This has resulted in the vehicles involved being split up, with the good end and mid section of one tram-train being coupled to the undamaged end of the other one. The swapped end has been renumbered to carry the same fleet number as the good end and mid section, so this vehicle isn't completely the vehicle it was when it entered service. Meanwhile the smashed up ends and other mid section have been put together and I believe they have now been sent back to Bombardier, who I think ought to send them back with bull-bars fitted!
As to the reasons for the accidents, I can only comment on the first one because I don't know the full details of the second. Apparently the lorry ran a red light. However the tram hit it in the side, so the tram hit the lorry, the lorry did NOT hit the tram. Although the lorry driver has been blaimed for the accident, I don't think this is entirely correct or fair. Trams (unlike trains) should always be driven on sight. In other words, the driver should only drive to what he or she can actually see ahead of them, just like road vehicles. Trains are not operated on line of sight, being totally reliant on signals. At the time of the incident, the tram-train was acting as a TRAM on the TRAMWAY, so should have been operating according to line of sight and should have been able to stop for any obstacles that came into view. As the tram hit the side of the lorry, which was already crossing the line, I believe the tram should have been able to stop. The fact it didn't opens up a whole host of questions. Was it travelling too fast? Did the driver apply the brakes? Did the brakes work? It seems strange that the Siemens built trams have been operating over that junction for over two decades without any major incidents, but the tram-trains have suffered two very similar incidents within a couple of months.
One thing I'm not sure of is how the braking system of the tram-trains works. The Siemens trams have a number of braking systems, including magnetic track brakes, which are long flat shoes that clamp down directly onto the track when activated. These are VERY effective and are not normally used except in an emergency because they could easily catapult the passengers through the windscreen. That's how good they are! But do tram-trains also have them? If they don't, that will definitely mean they can't stop as quickly. Maybe MadAnnie or Lemmy could enlighten me?
Finally... The whole 'experiment' is nonsence anyway! In reality wheel profiles don't actually matter all that much. provided the flange of the wheel will fit in the slot of grooved track, pretty much anything will work. It might not be ideal, but it will work. Historically this has been proved time and time again. Railway coal wagons used to make extensive use of the old Glasgow tramway. All they did in Glasgow was lay the tram tracks a quarter inch further apart so the railway wagons with their deeper flanges ran in the bottom of the grooves, not on the rail head. Also the Blackpool Loco, now at Crich, was originally used to haul yet more coal wagons on the Blackpool system, mainly between Copse Road Deopt in Fleetwood and a coal yard at Thornton Gate. It's not rocket science to make a tram run on a railway or a train on a tramway (Weymouth Quay anyone?)