Feel sorry for us Brits who have to deal with both, in a confusing mishmatch
Metric for most things, with some bizarre use of imperial for inertia reasons.
road/railway speeds - imperial(mph), scientific speeds, and any other speed, metric.
road distances (signs usually are in miles/yards or fractions), however, the distance markers on the side of the motorways used by workers, etc are in KM.
Car economy is in mpg (though our gallon is slightly bigger than the US gallon), but we buy our fuel in litres, and
pay for it in litres. Possibly a good thing considering the price.
Most items are bought in a supermarket are given metric mesurements for weight and volume, eg litres for drinks, grams/kg for food weights, yet MILK is still sold in pints.
Beer is still sold in pints in a pub....