Trains can only run on train tracks.
The tracks/train stations don't always go close to where the freight needs to go.
It is bordering on impossible to build new rail infrastructure to get freight where it needs to go.
It takes a lot longer to ship something on a train than on a truck.
Add on the fact that transport in general is getting more expensive, and I don't think more regulations on trucking is the right answer.
Just install the guards on the side of trailers and be done with it...