Traces of cannabis found in the blood of a motorist involved in a fatal motorway smash were not caused by passive smoking of the drug, an expert witness has told a court.
Anastasia James is on trial for causing the deaths of her 14-year-old daughter Destiny James-Keeling and her son's girlfriend, Megan Marchant, 18, by driving without due care while unfit through drug use.
Both victims were pronounced dead after James's Vauxhall Astra convertible crashed into a tree beside an unlit section of the northbound M1 in Leicestershire at about 7.15pm on January 4 2014.
Giving evidence on the second day of the trial, forensic scientist David Berry told jurors a blood sample taken from James showed the presence of cannabis's major active constituent, THC, at a level of 2.4 micrograms per litre.
Mr Berry told Leicester Crown Court that the sample - taken at 1.01am on January 5 - also showed a THC acid level of 20 micrograms per litre of blood.
The witness, a fellow of the Royal College of Pathologists, said of the THC reading: "In my view the concentration of THC is likely to cause driving impairment, particularly in a naive or occasional user.
"The combination with low THC acid suggests she smoked cannabis shortly before the accident."
Prosecution counsel Michael Evans QC asked Mr Berry: "Is there any possibility that the levels could have been caused by Miss James inhaling cannabis being smoked by someone else in the vehicle?"
Mr Berry replied: "My answer is no. This is impossible."
Analysis of samples taken from the deceased showed no traces of cannabis, Mr Evans then told the court.
Under cross examination by defence QC James House, Mr Berry was asked whether he was prepared to accept the possibility that the blood sample findings could be explained by the smoking of cannabis in the days or weeks before the crash.
Mr Berry answered: "No, I think it must have been smoked on the day."
The court has heard that James told police in interview that a fault with her car must have caused the crash near the intersection with the M6.
The 37-year-old, of Thornton Close, Braunstone, Leicester, also told officers that she had not smoked cannabis on the day of the accident and had last used the drug "ages ago".
James denies the charges.