The world is a very different place to 60 years ago. We cannot base policy decisions on data collected before the majority of people were even born!
I'd be all for a new study, but to use data when just a fraction of the cars were on the road compared to now would be silly.
Not only that, but working habits have changed, more kids get lifts to school, people commute further, the types of roads have changed (we have more motorways now for example), before you even get to the massive increase in traffic in the last 60 years.