England's motorway network is not safe enough to have the speed limit raised to 80mph, according to a new report from the Road Safety Foundation.
Poorly-maintained and inadequate roadside protection and the rapidly rising risk of shunt crashes from the sheer volume of traffic using England's motorways are key factors of safety concern in the Unfit for 80 report.
The Road Safety Foundation report said that currently motorways do not provide enough protection to drivers and car occupants to consider raising the speed limit.
It shows widespread faults in run-off protection which are doubling the rate of death and serious injury where there is missing protection.
It shows shunt crashes rise exponentially with increased traffic flow, yet only a handful of motorway sections like the M25 and M42 have the electronic controls with hazard warning and variable speed limits that are needed to manage the intense flows common across England's motorways.
Director of the Road Safety Foundation, Dr Joanne Marden, who oversaw the new research, said: "The vehicle fleet has become safer in the last decade through better crash protection. At motorway speeds, the car alone cannot protect the human body.
"The car has to work with the motorway's protection systems such as safety fencing to absorb high speed crash energies. In the next decade, the greatest potential for reducing deaths is on higher-speed roads outside built-up areas. This will be delivered through crash avoidance technology and road engineering catching up to complement improved vehicle crash protection."
Run-off protection is critical in preventing deaths and serious injuries from single vehicle run-offs.
Dr Marden said: "Our cars provide 4-star or 5-star crash protection but too many of our motorways rate only 3-star with major weakness in run-off protection.
"England's most heavily trafficked motorways can carry a million vehicles within a week. But a one-in-ten million combination of circumstances can arise every three months. Even though they may seem minor, the rate of exposure to any risk is so intense that even minor flaws in motorway layout or safety provision are likely to have serious consequences sooner rather than later.
"These 'unusual' circumstances include pedestrians on the hard shoulder, roadworks, extreme weather, spilt loads and rear-end shunts when free-flowing traffic breaks down."
The report outlines the negative economic effects of a higher speed limit, which include increased vehicle operating costs through higher fuel consumption; increased crashes and crash severity, resulting in raised crash costs; and the increased cost caused by delays from crashes.
The report said if 80mph is to be trialled, it must be on controlled motorways such as sections of the M25 and M42.