All made to a little used S Scale (1:64) but none the worse for that in themselves until matching up with scenery made to OO/HO scale etc. Run on regular OO tracks.
Corgi took some large liberties with many of the models adapting or changing the prototypes to fit the three-bay body design though the many variations of closed/open top/open upper deck/lower deck vestibules help to widen out the range considerably.
Can be motorised - see individual suppliers also on eBay.