David Cameron today confirmed the Government would outlaw drug driving as he praised the family of a schoolgirl killed by a cannabis user for their "brave" campaign to change the law.
Lillian Groves was 14 when she was knocked down and the driver went on to serve just four months in jail.
The Prime Minister said it "simply can't be right" that the laws were not in place to punish drug drivers properly.
Motorists under the influence of illegal substances can only currently be prosecuted for being behind the wheel if police can prove their driving has been impaired.
Mr Cameron said: "I found meeting Lillian Groves's family in Downing Street late last year incredibly moving. As they said at the time, it simply can't be right that a schoolgirl like Lillian can lose her life and then we discover we don't have the laws or the technology to punish drug drivers properly.
"We want to do for drug driving what drink driving laws have done for driving under the influence of alcohol. That's why we're doing what we can to get drugalysers rolled out more quickly.
"And this week we'll publish a new drug driving offence so that driving under the influence of drugs itself is a crime, just like it is for drink driving.
"Lillian Groves's family should be congratulated for their brave campaign. I hope now that something good can come out of their tragic loss."
Under the crackdown, proposed as part of a wider Crime, Communications and Court Bill in the Coalition's new legislative programme, drug driving will become a specific offence.
Offenders will face up to six months in jail and fine of up to £5,000 as well as an automatic driving ban of at least 12 months.
Police will carry a handheld drug detection devices, which will take a saliva sample, as well as a breathalyser to test erratic drivers.
The machines are expected to receive approval from the Home Office by the end of the year.
Road Safety Minister Mike Penning said: "Drug drivers are a deadly menace - they must be stopped and that is exactly what I intend to do.
"The new offence sends out a clear message that if you drive whilst under the influence of drugs you will not get away with it.
"We have an enviable record on road safety in this country and I want to keep it that way.
"This measure will help to rid our roads of the irresponsible minority who would risk the lives of innocent motorists and pedestrians."
The move follows an independent review of drink and drug driving law in 2010. An expert panel will help to decide which drugs are covered by the offence.