More people are driving under the influence of drugs in Ireland than ever before, according to the Medical Bureau of Road Safety.

The Department of Transport will now draft the Road Traffic Bill so that a garda can form an opinion if a motorist is taking drugs.

MBRS director Professor Denis Cusack said these tests will include cognitive tests, such as walking in a straight line, tipping your nose or counting while standing on one leg.

It is also trying to find a suitable device to carry out roadside testing for drugs.

Professor Cusack said: "Unlike alcohol, there is no legal limit for drugs. Under current road traffic law, the gardaí must be satisfied that a driver is under the influence to such an extent as to be incapable of having proper control of a vehicle.

"This means that the garda has to prove driver impairment to the satisfaction of the court and this can cause difficulties in successfully prosecuting such offences."

It has been an offence to drive under the influence of drugs in Ireland since 1961.

Minister for Transport Leo Varadkar asked the bureau to investigate the options in January.