Live lane traffic incidents have increased on sections of the M25 where the hard shoulder has been used for running traffic, MPs have been told.
Metropolitan Police told the cross-party Transport Committee that there was also “clear evidence” of a “significant” rise in reported near misses.
The body was giving evidence to an inquiry into all-lane running, which has been introduced to sections of six motorways in the UK and is expected to be rolled out further.
“The Metropolitan Police Service must repeat its continued objection to all-lane running in its existing form,” warned the written submission.
“The significant risk (of collisions likely to lead to serious or fatal injury) it represents is insufficiently mitigated by the existing driver information signals and emergency refuge areas, which we feel are inadequate in both design and spacing.”
Metropolitan Police said that the overall number of road traffic collisions was likely to reduce when all-lane running was introduced. But it said this was mainly because of variable speed limits, which could be introduced without removing the hard shoulder.
“The type of collision that all agree will significantly increase – one resulting from a broken down vehicle in a live lane – is far more likely to result in serious injury or fatality than many of the collision types that are actually reduced,” it warned.
Highways England told the committee that collision rates had fallen by almost a fifth between junctions 23 and 27 of the M25 since all-lane running was introduced.
It added that by attracting vehicles to motorways, the scheme was keeping more traffic on the country’s safest roads.
Highways England said using all-lane running provided a 33% boost to capacity for 60% lower cost than traditional road widening.
“The smart motorways concept has evolved greatly,” it added.
“Not only has this evolution led to greater cost efficiency, it has also led to improved traffic flows and increased journey reliability for road users, while maintaining safety.
”It is clear that the concept has to continue to evolve and take advantage of technological advancement to continue to improve safety, improve our service to customers and to enable further step changes in efficiency.”