I know that implementation of metric speed limits on the US an UK roads has been often characterized as something that may cause safety issues. Does the trucking industry perceive driving the trucks between metric and nonmetric countries as something of a safety hazard? Do they provide their drivers training or warnings regarding different units of speed being used on the roads? And, are the truckers who travel between US & Canada/Mexico, or UK & Continental Europe/Ireland more likely to be involved in accidents?

I think (but I cannot be sure) that UK truck speedos have main km/h dials and mph inner dials.

They tend to have a stamp on the back that says 'limit to 56mph' which obviously translates to a round metric value.

Other than that I'm not sure to the rules (martin!!???) however the interesting thing is that in trucking "parlance" imperial is used despite the idea of metric speedos (imperial under).

BTW - when I was in spain I noticed their buses had km/h (mph) but the buses were british made.

In the UK I've seen bus speedos either way around

There is tremendous cross border traffic between Michigan and Ontario, mostly automotive related, at Detroit-Windsor and Port Huron-Sarnia crossings. I'm aware of a few height issues, and some of our bridges have added dual marking so that may be an issue. There is NOT a program to dual label every bridge; it is selective, I assume driven by accidents or key routes.

I've never been in a heavy truck cab, so I don't know if they commonly have dual speedos (cars do). I would observe that trucks don't even obey the car limits (truck limits are lower) on either US or Canadian freeways and are among the worst offenders. But it is not a speedometer issue. They are in a business where "time is money." You have to drive well over the speed limit to stay ahead of the trucks (I dislike being passed by them) and that is true well away from the borders. I can assure you that you don't find a Canadian trucker going 65 km/h in a 65 MPH zone. As for an American trucker going 100 MPH in a 100 km/h zone, he would if he could but he has to settle for 80-85 MPH.