Ryan Hagger, 28, ploughed into the back of a van as it waited to turn right on the A10 between Royston and Melbourn at about 1pm on 27 January last year.
His Vauxhall Insignia then collided head-on with a Ford Fiesta being driven by Jeanette Spencer, 50, of The Pyghtle, Buntingford, who died at the scene.
Officers arrived and Hagger tested positive for cannabis following a roadside drugs test.
Investigations concluded Hagger had travelled to Royston to meet his partner for a fast-food meal during his work lunch break.
On his return journey he had been following the van, which had indicated and slowed. But despite plenty of warning and a good view ahead, Hagger failed to react.
Hagger, of Beechside, Gamlingay, pleaded guilty to causing death by driving without due care and consideration while over specified limit.
He was sentenced at Peterborough Crown Court today (25 March) where he was jailed and disqualified from driving for three years.
Detective Sergeant David Burstow, from the serious collision investigation unit, said: “This is a stark reminder of the dangers of driving while impaired through drink or drugs. Cannabis slows the reactions and, in this case, caused the worst possible outcome. Do not use drugs and drive.
“Our thoughts remain with Jeanette’s family during this very difficult time.”
The force operates a dedicated, confidential hotline for members of the public to report drink or drug driving. The hotline, 0800 032 0845, is available 24/7 and gives people the chance to supply the police with information to help reduce the number of drink or drug drivers on the county’s roads.
For more information about drink or drug driving, the law, and the dangers it can cause, as well as the confidential hotline, visit the force's dedicated web page: https://bit.ly/382ZKgB.