Department for Transport (DfT) traffic projections for England and Wales show delays may rise by up to 85% from 2025 to 2060 in that scenario.
The analysis is based on connected and autonomous vehicles making up half of the car fleet by 2047, and a “fast uptake” of electric vehicles.
This would lead to more traffic by “increasing the mobility of the elderly and those who do not currently hold a driving licence”, according to the report.
But the document, published last month, claims “the ability to work or relax while travelling in a self-driving car” means occupants will be “more amenable to sitting in traffic”.
RAC Foundation director Steve Gooding told the PA news agency: “There are currently 5.9 million licence holders aged 70 or over in Britain, so we know the demand for mobility is there among those of a senior age.