A BRITISH CONCEPTION OF TRAIN:

But what about trams? They have to operate in mixed traffic conditions ie with normal road vehicles. They don't need signals. They seem to stop all right. So, why don't they have this problem? Is it the speeds involved? Or is it because they are lighter? And if it is because they are lighter why not make trains lighter and get rid of the signals?

To do so would be to throw away the advantage of a train, which is to move thousands of tons of Powder River coal with little rolling friction, albeit with lots of momentum to master. Some of the comments on this post recognize the point.