On Alfa number 15
AO Platinum Member
Join Date: Dec 2005
Location: United Kingdom
They are both at equal risk of failure IMO.
The motorway miles are easier on the belt, but of course it has done more of them.
The tensioner bearings in the higher miler may be more worn, because they have done more revolutions, however the belt itself takes a lot of load at slower speeds and when starting the engine.
Plus of course the fact that the belt deteriorates with age, heat cycles and loading as well as wear take an affect.
It isn't worth the risk, if it is 3 years old or has done 36,000 change it. It will work out cheaper than an engine rebuild.
You will never be cool driving a Vauxhall.