EXPANDED THOUGHTS HERE:
You don't have to be a statistics boffin to see the flaws in this projection. Clearly, the UK's love affair with motoring is tailing off. It has reached its peak and it's now on the classic downward bell slope.
However, DfT - and the RAC Foundation which uses the graph in its report 'Keep The Nation Moving' - have ignored the downward slope and plotted a weird v-shape to make the graph go sky-wards. Why? To build more roads.
Look at the early 1970s. Traffic demand flatted out, and this was in an oil crisis. The latest figures don't show a flattening out of demand, they clearly show a reduction in demand.
We don't need more and more roads, they're incredibly expensive to build and - long-term - even more expensive to maintain. It's likely we won't need them so why build them?
Why can't the DfT - and RAC Foundation - see what's clearly shown in this graph? Mass motoring was so last century.
I'm interested in this stuff because I'm writing a book on the history of roads (and the forgotten contribution cyclists made to the roads of the UK and the USA). In the UK, only 1 percent of roads were specifically built for motorised vehicles. Add motorway-style trunk roads into the mix and you get 13 percent of UK roads which are mainly motorised vehicles only.
The majority of roads were not built for cars.
In the 1880s, cycling bodies in the UK and USA were the first bodies to push for road surface improvements. In the UK, the Roads Improvements Association paid for road trials of surface treatments, including asphalt and organised the first conferences on roads. The RIA was started as part of the Cyclists' Touring Club. In the US, cyclists were even more influential. US presidents used to attend the AGM of the League of American Wheelmen.
Motorists clamour for the blackstuff but they need to thank cyclists for its adoption.