The number of people being charged with impaired driving is dropping, but anti-drunk-driving advocates and some police say that's not because there are fewer impaired drivers on the road.

Figures compiled by Statistics Canada show the number of people in Canada slapped with drunk-driving charges over the last 20 years has been cut in half.

The statistics — gathered at the request of Mothers Against Drunk Driving Canada — show the number of adults and youths charged with impaired operation of a motor vehicle with a blood alcohol content of 80 milligrams or more per 100 millilitres dropped from 117,514 in 1986 to 56,617 in 2006.

The number charged with impaired operation of a motor vehicle causing bodily harm declined from 1,239 to 812 over the same period.

Anti-drunk-driving advocates say they are worried the number of drunk drivers on the road is not really dropping, but that police are actually laying fewer charges due to problems with Canada's impaired driving laws.

Toronto police traffic Sgt. Tim Burrows said the amount of paperwork it takes to process an impaired driving charge means it could take an officer almost half a shift to process a single one.

"There's more paperwork now. The level of expectation from the courts for what we need to put forward is a very, very high level because drinking and driving [charges] affect so many things," he said, including information about the accused's licence, insurance and employment status.

"It's made our job a lot harder in terms of the prosecution of that, the collection of evidence, and the time consumed to process an impaired or an over 80 [milligrams] charge," Burrows said.

Senior police sources who work in traffic enforcement told CBC News that when they do put in the time required to lay an impaired driving charge, it's discouraging to see people enter plea bargains in which they plead guilty to careless driving charges, as the courts and Crown prosecutors try to reduce court backlogs and the number of trials.

"If you're a brand new police officer, I can easily anticipate one of my officers being off the road for at least four hours from beginning to end … and that [doesn't] necessarily mean it's going to be a completion," Burrows said, adding that most of that time is used for taking down written observations, or notes, about the alleged crime.

Defence arguments gain sophistication

On top of that, police sources said it's frustrating to see many accused impaired drivers beat the charges in court as defence lawyers arm themselves with increasingly sophisticated arguments.

Robert Solomon, a law professor at the University of Western Ontario who has crunched the Statistics Canada numbers on behalf of MADD, agreed the law is too cumbersome. As a result, he said, some police officers are laying lesser charges, such as roadside suspensions under the provincial law, in borderline impaired cases.

"We have statistics, national surveys of police, where police indicate — 30 per cent of them — that they will not lay an impaired driving charge against a driver, even if they think he's guilty of impaired driving, even if they have evidence," Solomon said.

Burrows admitted that some officers will give borderline drunks only a short-term suspension if it helps get the impaired driver off the road faster, and the officer back out on the job.

"Some officers might believe that if we do this expedient matter … we give a 12-hour suspension … we get that driver off the road …we've done the due diligence, in the fact that we made the road safer for that limited period of time."

MADD Canada is calling for an overhaul of impaired driving laws to make it simpler for police to ensure every driver who tests over the limit can be charged criminally.

With files from Dave Seglins