The case has again raised questions about the zero-tolerance approach of the ACT's drug driving laws, which, unlike drink driving, do not measure whether a driver is impaired.

The man, 45, was riding his Harley-Davidson south on Tharwa Drive in January, when a Land Rover pulled out in front of him.

The crash left him with horrific injuries.

He suffered a broken pelvis, three fractured vertebrae, broken ribs, a broken tibia and fibula in both legs, a broken femur, a dislocated shoulder and a pulverised kneecap.

His left big toe had to be amputated, and he required a donor kneecap and tendon for his left knee.

The rider was in a coma for 10 days, causing a pressure sore on the back of his head. He also needed dialysis for two months due to kidney failure.

The recovery is expected to take many years, and he remains in a wheelchair five months later.

As is legally required, doctors took a blood sample and found a trace of cannabis.

The man, not a regular drug user, had smoked a small amount of cannabis at a party on Saturday night.

The crash occurred on Monday at 5pm.

But the ACT's drug driving laws make it illegal for any trace of an illicit drug to be in a driver's system, similar to most Australian states.

That's a different approach to drink driving laws, where minimum thresholds of alcohol concentration in the blood are mandated to reflect whether a driver's ability is impaired.

The rider was charged with

The court heard there was no evidence whatsoever that he was impaired at the time of the crash, and that he was not at fault in the crash.

Magistrate Peter Morrison described the case as exceptional, and made a non-conviction order.

Civil Liberties Australia vice-president Tim Vines said drug driving laws, designed for road safety, are not designed as a way to simply outlaw drugs.

"Because we've got this zero-tolerance approach to drugs in the system, we don't send out a targeted message to people, other than 'don't do drugs'," he said.

"People should really be looking at what level of impairment is actually a risk to public safety, and then the tests and the thresholds should be based around that."

The issue of whether to take a zero tolerance or impairment-focused approach has split many countries.

In Europe, for example, the Czech Republic, Denmark, Germany, Greece and Spain base their laws on impairment, while Bulgaria, France, Poland and Sweden have a zero-tolerance model.

Other countries, including some parts of the US, also employ behavioural impairment tests, such as walking in a straight line, the one-legged stand and measuring pupil size and responsiveness.

The ACT's drug driving laws were introduced in 2011 to try and deal with the significant and dangerous problem of drivers getting behind the wheel while high on drugs.

Random drug tests can be conducted, testing oral fluid followed by a confirmation blood test, and tests are also taken after serious crashes.

In 2013, another questionable case came before the court involving a senior public servant who ate a breakfast muesli containing hemp seeds before riding her motorbike.

Her husband was a dietitian who had been making her a special gluten-free muesli, causing the low level of THC found in her system.

The case jeopardised her job in the public service and threatened the strict national security clearances she had needed.

Her nine-month court battle was described as "traumatic", and she was also given a non-conviction order.