A trike is just another cool term by the Google Folks – nothing technical about it. I think some folks wanted Bikes, and the others wanted Tricycles. And since grown-up folks dont ride tricycles (unless they sell icecreams), they named these three wheeled bikes as trikes. These are going to be going around all around UK – where there still exists a lot of places where the Google Street view cars cannot go – and I mean places like side walks, walkways etc. One thing I noticed that would prove useful from this, is going to be castle tours and tourist attractions of the likes. People can now get a street view of these attractions, before even going there (or for lazy folks, they can see these from their couches and satisfy their touristy appetites).
See the cnet article here.