The RAC Foundation has called for a review of the length of time roads are shut by serious accidents.
It claimed such closures cost the country at least £5 billion every year and accounted for a quarter of all congestion on the roads.
And although police should be able to investigate fatal accidents thoroughly, the foundation said traffic should also be kept moving through the sites of any accidents as much as possible.
A total of 86 motorways in England were each closed for at least three hours in the last three months of 2008; the entire year saw just 136 fatal crashes on motorways across the UK.
The RAC Foundation has issued a report compiled by Irving Yass, a one-time Whitehall transport specialist. Its findings state that the police are instructed to treat fatal crashes as "unlawful killings" until they can prove the contrary.
The number of crash investigations is not recorded nationally, neither is the number of prosecutions which result from them, according to the report.
It also says that no standard practice exists in police forces across the country in deciding when to send investigators to road traffic accidents in which no one has been killed. London, Essex, Humberside and Surrey police forces investigate around three times the number of actual fatalities which occur.
Stephen Glaister, the foundation's director, said: "Closed roads can cause major congestion, huge losses to the economy and in the worst cases even more accidents. The right balance has to be found between delivering justice and keeping the country moving."
Chief Constable Mick Giannasi, the Association of Chief Police Officers' member responsible for road policing, said: "Roads policing in London is vastly different to roads policing, for example, in Dyfed Powys and a one-size-fits-all solution is neither realistic nor desirable. For this reason I do not believe that a fundamental review of roads policing is necessary."
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