[penthehuman]

You have to start somewhere though, it can be a transition over time as well. Say a law was passed that all new roadside signs erected from date X will have both m and km, then at date y, years down the road, all new signs only list km.

For cars, just use the same dials and displays they use in Canadian cars, metric is the primary unit with imperial also shown, again, on new cars only, no need to retrofit all old vehicles.