The volume and weight of traffic has changed too - with more and heavier cars, trucks and buses on more roads - and this will have affected some streets more th

The volume and weight of traffic has changed too - with more and heavier cars, trucks and buses on more roads - and this will have affected some streets more than others. Quiet residential dead-end streets will barely change, while rat runs and secondary routes may be seeing significantly more traffic than they were ever designed for. Equally, main roads may have been massively overengineered at some point in the past and therefore able to cope with the increase. There's a lot more going on there than just the layer at the top.