Nathan Virgo drove at excess speed in a Mercedes Sprinter van on the westbound carriageway at Hangleton on August 9 last year.
The 43-year-old delivery driver attempted to undertake a BMW SUV at high speed and ended up spinning to face the wrong way on the dual carriageway.
The BMW driver was left trapped with serious injuries in the wreckage of his vehicle which flipped onto its side on the grass verge after being hit by Virgo’s vehicle.
Emergency services were called and the A27 was closed for more than two hours while the man was extracted and then taken to hospital.
Virgo was arrested at the scene on suspicion of drug-driving after completing a roadside DrugWipe test which was positive for cannabis, and also on suspicion of dangerous driving.
At Brighton Magistrates’ Court on March 16, he admitted the two charges and a further charge of being found in possession of cannabis.
Virgo, formerly of Coleridge Crescent, Goring, but now of HMP Brixton, was sentenced to three months in prison.
The court also disqualified him from driving for 2 years and ordered him to pay a £128 victim surcharge and £85 costs.
On August 9, it had been raining both overnight and in the morning with heavy downpours, leaving standing water on the carriageway.
Witnesses described how Virgo had driven at high speed to undertake several vehicles before attempting to move into the outside lane.
He cut in front of the BMW driver, who had no time to react.
The driver suffered injuries and was taken to the Royal Sussex County Hospital. He continues to make progress with his recovery.
Virgo later gave a positive blood test which showed he had 8.2 microgrammes (mcg) of cannabis in his system per litre of blood. The legal limit is 2mcg of cannabis per litre of blood.
Investigating officer, PC Steve Bucksey of the Roads Policing Unit, said: “Virgo’s dangerous driving put his own safety and the safety of other road users at risk.
“At the scene, we found that Virgo was driving while under the influence of cannabis. He told us he smoked cannabis the night before but still felt fine to drive, despite being four times the legal limit. Unlike alcohol, Drugs can take days and even weeks to be within legal limits”.
“Driving under the influence of drugs and driving at excess speed are two of the main reasons why people are killed and seriously injured on our roads.
“Virgo caused several hours of disruption and is incredibly lucky that this collision did not have tragic consequences.
“This case demonstrates the risks of drug-driving and driving at excess speed. It also shows the obligation of all motorists to ensure they drive appropriately according to road conditions.
“We will take appropriate action to remove those that endanger other road users and I am pleased that a dangerous driver has been taken off our roads.”