Not sure where you're getting the population figures, as looking around the 'official' figures vary an awful lot.
How come those clever buggers who based road damage on axle weights alone (influenced?) never took into account the scrub effect of three axled vehicles, both tractors where in most cases two axles are usually non steer and trailers where three non steer axles are the norm, which are causing the massive road wear we see everywhere, let alone 44 tons repeatedly over undulations with suspension bounce increasing the weight imposed on the same road sections repeatedly every few seconds...we all know these sections because as you drive along you can see black marks (not from braking) developing where the tyre load has increased as axle after axle thousands of times a day repeatedly hits the same spot.
The two that spring to mind for me have recently been resurfaced, the worse being the A34 northbound by the A44 turn at Oxford, that bump could empty your cubbies, and the M6 n/b at jct 4 in the second lane (most heavily lorry used) of the 4 lane section just before the M42 diverges.
I know these sections because i've travelled them almost daily for ever, you will know of similar on your travels, easily identified due to the tyre marks.
We simply didn't see the massive road damage to the same extent in the day of 32 tons on 4 axles, because with most vehicles it was either the tandem of the trailer doing the scrubbing, far less than a triaxle, or the twin fixed axles of 6 or 8 wheeler, which didn't and still don't turn as tight as an artic trailer for obvious reasons.