MOTORCYCLISTS are almost always at fault in fatal bike accidents.

In a startling new analysis that has prompted police to launch a crackdown on bikers, research into fatal motorcycle crashes over the past 12 months found four out of five riders were to blame.

And more than half the riders had alcohol or drugs in their system either above the legal limit or high enough to impair their judgment.

The research also discovered that nine out of 10 killed riders had traffic records. Some had been charged multiple times for reckless driving, drink-driving and speeding.

In addition, half the 30 bike fatalities in WA between January 2012 and April this year involved riders on an unlicensed bike, or a bike that had been in their possession less than three months.

Riders aged 25 to 40 were identified as being most at risk.

WA Police Assistant Commissioner Nick Anticich said the study proved bike riders were major risk-takers. He said it completely tore apart "the belief held by most motorcyclists that other road users cause most crashes involving motorcycles".

"The stats also tell a grim story about risk-taking," he said. "Most had drugs or alcohol in their system and most had a history of traffic offences. Put those two things together with the extremely high risk that comes with being a new or returned motorcycle rider and we are talking about a very, very high risk of being involved in a serious or fatal traffic accident.

"Police need to do more to target motorcyclists for this reason and we will be doing that, but motorcyclists need to urgently take stock, too.

"People won't like this, but I'll say it: If you want to avoid being killed or suffer a serious injury, from a pure statistical perspective you should not be getting a motorcycle."

Mr Anticich said police would crack down on reckless riders. "It's not about being vindictive towards motorcyclists as a road-user group, it's because we see that they need protection from their own behaviour," he said.

Department of Transport figures show there are 96,882 registered motorcycles in WA, but there are more than 302,000 motorcycle licence holders.

Motorcycle Riders Association of WA vice-president Dave Wright said: "We certainly encourage more motorcyclists to take extra care.

"Motorcyclists need to watch out for cars, cars need to watch out for motorcyclists and there has got to be that personal responsibility there."

In the past fortnight, four motorcyclists have been killed, including three in three days this week.