A car overtaking in wet conditions on the M1-A1 link road
The M1 between Leeds and Wetherby fails to meet modern construction standards and could be unsafe in heavy rain, a BBC investigation has revealed.
Using the Freedom of Information Act, the BBC obtained a report commissioned by West Yorkshire Police after a fatal accident on the motorway in 2004.
It shows that the M1-A1 link road was built with an outdated drainage system.
The Highways Agency said improvements have been made but that drains still do not meet the latest requirements.
V-shaped channels alongside the carriageway funnel rain water through grates into catchpits beneath the ground, and then into the drainage system.
The Department for Transport twice tightened the minimum standards for this type of drainage during the motorway's construction between 1996 and 1999.
The improved standards require three times the number of grates to increase drainage efficiency.
The Highways Agency said in a statement that when the road was designed in 1995, it did meet standards then in place.
It continued: "After the accident in 2004, there was a review of the drainage system and as a result of this improvements were made to increase the size of the drainage gratings at five locations."
Drainage channels are now checked daily and the agency also reviews accident records.
It said the accident rate was below the national average for this type of road.
"However, the Highways Agency is not complacent and continues to monitor and respond accordingly," it added.
Paul Mason holds a newspaper report of his accident
The findings of the confidential report have alarmed road safety experts.
Edmund King, director of the RAC Foundation, said: "In this case it would appear that the latest specifications for drainage, which were introduced twice while the scheme was being constructed, were not adhered to.
"It appears that has made the road more dangerous and if that has led to more aquaplaning then that is an incredibly serious problem."
The report also angered motorist Paul Mason who survived a serious accident after hitting water on the M1-A1 link road.
He was not prosecuted after losing control of his vehicle which smashed through a fence and rolled down an embankment.
"The police told me that if there was ever a court case they would support me because there had been so many problems with that section of the road," said Mr Mason.
"I feel quite bitter about it because clearly the drainage was inadequate."