By the Buddhist laws, you are not allowed to ride or drive anything, they suppose to walk or go with someone on their vehicles, that way they are not killing any insects, animals or pedestrians on the roads, either intentionally or unintentionally. These days some monks even drive a car.
I wonder about this myself. Perhaps the federation of lao bouddhism could shed some light on this matter. All I know is that monks of today and those of over two thousand years ago are living in a totally different way of life. Evolution is just following its own course - things that can be changed ...will change. Just like everything else.
