Speeds and distances will probably change eventually, but it's difficult to do because you'd need to change all of the road signs in the country and there would be massive confusion if you only changed some of them - you'd probably need to mark all of the metric ones with some symbol indicating that they were metric over the transition period.
It's not hard to write "km/h" behind the number on the road sign; that's actually standard in some countries. I'd guess there might still be some confusion, but that's mostly a matter of lacking common sense and/or the desparate try to find excuses ("Honestly, officer, I'd swear that road sign said 130 mph and not 130 km/h!").