Each hex is 75 meters accross - each round is 30 seconds
hexs/hour == k/hr * 13 1/3
hexs/30 sec == hexs/hr / 120
so
hexs/30 sec == k/hr /10
Thats close enough for government work -
so a jeep (tl5 p287), starting stationary on a road spends a round accelerating (by it's accel rate) and is now travelling at 12 km/hr -> 1hex per turn (2 every 5 turns).
A couple of turns later, it accelerates to 25km/hr and is now moving 2.5 hexes per turn (ie 2 then 3 then 2 etc)
and so on.
Unless it was important, I would try and keep all speeds to a whole number of hexes per turn (you can't do this for slow things - but they are rare)
At least that's my interpretation.