The finding will be revealed by the RAC Foundation's director Edmund King, in a presentation at The Transport Times conference in London today.
The new report from the Road Users' Alliance reveals that Britain has more cars per motorway mile than any EU-25 nation.
Rather than the UK network competing against France or Germany, it is more in line with Lithuania, Slovakia and Hungary.
In his presentation, King will also highlight the fact that the UK has lower car ownership rates than many European nations but worse congestion.
He will make the case for urgent road improvements, coupled with the introduction of a voluntary road pricing system based on a pilot in Oregon, USA.
Mr King said: "Roads in the UK are essential for 92% of passenger traffic and 88% of our freight. This reliance on the road network will continue even if public transport is radically improved.
"We need road improvements but we also need to question when and where we travel.
"Research findings from a pilot in Oregon show that even a voluntary system of road pricing where drivers pay per mile but receive a discount on the cost of fuel has lead to a reduction in peak period traffic of 20%.
"Even if only10% of drivers opted to pay for their motoring in this way it could have a significant effect in reducing traffic congestion."