Responding: the 150 m.ph. is for passenger trains but only outside the tunnel on the high speed track. Inside the tunnel, which is about 30 miles long, speed is around 75 I believe. The tunnel is not straight, it curves quite a bit. This is due to builders following the easiest rock strata for tunnelling. But being all chalk it was not too difficult, except for the length of it.
Two types of railcars are used, one is shown on Luke's photo, that one is a full-height one used mainly for buses and high cars/vans, ---and motorcycles usually get put in there as you can see. Others are double deck for normal size cars. The second type is not closed in, it does have steel-mesh sides, it's used for trucks. Truck drivers don't stay in their cabs, there is a passenger coach for them.
The regular passenger trains (London-Paris) are completely different, more like the US Amtrak trains I imagine but designed for high speed.
