Author: Dalgarno Institute

A car travelling at 100 kilometres per hour covers 28 metres every second. At that speed, the difference between a driver whose reaction time is normal and one whose cannabis has compromised is not a policy debate. It is a body count. Cannabis and road safety has become a crisis hiding in plain sight, and the gap between legalisation and public health has never been wider.

The BUILD for America’s 250th Act, a bipartisan transportation bill introduced in the United States House of Representatives, contains provisions that should have existed the moment the first state legalised recreational cannabis, a direct failure of cannabis and road safety policy that has cost lives. The bill directs federal agencies to study cannabis and polysubstance impairment on driving, propose evidence-based impairment standards, and establish a national drug-involved crash data collection system. Lawmakers got these right: sensible, necessary, and long overdue. They are also a measure of just how far cannabis and road safety has been allowed to drift apart while legalisation moved at speed and public health kept quiet.

The Gap Has Always Been There

Alcohol has a legal limit. Decades of research have refined the science behind it. There are reliable roadside tests, trained officers, established protocols, and clear legal consequences. None of that infrastructure exists for cannabis in any comparable form.

The problem is not that cannabis impairs driving. It does. Research consistently shows that cannabis use slows reaction time, degrades divided attention, narrows the visual field, and disrupts the tracking ability required to maintain lane position. A driver under the influence of cannabis is not merely relaxed. They are operating a machine in a state of compromised neurological function while frequently unaware of the degree to which their performance has deteriorated. That unawareness is itself a feature of the impairment.

Why Cannabis Is Harder to Measure

The problem is that unlike blood alcohol concentration, which correlates reliably with impairment level, THC concentration in blood does not. Frequency of use, body composition, and method of consumption all change how THC metabolises. A regular user may register high blood THC levels yet show limited behavioural impairment. An occasional user can be significantly impaired at lower blood concentrations. Industry and advocates have exploited this pharmacological complexity for years to argue that impairment standards are too difficult to establish. The BUILD Act’s call to study the issue and propose standards is a direct response to the cannabis and road safety gap that has widened with every new legalisation. Lawmakers should have addressed it before legalisation reached the scale it has, not a decade after.

The road does not care about your tolerance level.

What the Data Shows

The United States Department of Transportation’s own position, restated clearly this month, is that marijuana use is not compatible with safety-sensitive functions. Truck drivers, airline pilots, and other safety-critical workers cannot use medical cannabis without consequence, regardless of whether a doctor has prescribed it and regardless of the Trump administration’s move to reschedule it. The reasoning is straightforward: rescheduling changes a substance’s regulatory classification. It does not change what happens to a person’s cognition when they use it.

Studies examining fatally injured drivers have shown that cannabis presence has increased steadily alongside legalisation. Research on crash risk has found that cannabis use approximately doubles a driver’s collision risk. When cannabis is combined with alcohol, the risk multiplies further still. The data on polysubstance impairment, which the BUILD Act specifically includes in its mandate, is particularly concerning given the normalisation of casual combined use across legalised markets.

The national crash data collection system proposed in the legislation addresses a critical blind spot. Currently, states collect toxicology data inconsistently, jurisdictions cannot share it, and gaps remain everywhere. Linking crash data with medical, coroner, hospital, and emergency services records, as the bill proposes, would for the first time give the United States a coherent national picture of how drug-involved driving is actually affecting road safety. That picture will not be comfortable viewing. It should be gathered and published regardless.

You cannot manage a problem you refuse to measure.

Legalisation Ran Ahead of Safety

There is a direct line between the cultural normalisation of cannabis and the erosion of public understanding that driving stoned is dangerous. In the same period that multiple US states moved to legalise recreational cannabis, survey data showed consistent increases in the proportion of people who did not believe that cannabis impaired driving significantly. This is not coincidence. When a substance is marketed, taxed, and sold in branded retail stores, retailers and governments send a social signal that it is a normal consumer product. Most people do not understand normal consumer products to affect their ability to operate a vehicle. The signal was wrong. The consequences have been material.

Transportation Secretary Sean Duffy put it plainly when he said: “At a time when culture is pushing and celebrating the use of marijuana, we’re not talking about the risk.” That is precisely the problem. The commercial apparatus of legalisation has invested heavily in normalisation. The public health and road safety apparatus has invested comparatively little in counterbalancing the message, and cannabis and road safety has paid the price. When a 19-year-old in a legalised state can walk into a dispensary and buy cannabis products from staff trained to discuss flavour profiles and potency, but has never received clear information about what those products do to their driving ability, the system has failed in a fundamental way.

Legalised does not mean safe behind the wheel. It never did.

What Standards Must Actually Do

The BUILD Act’s requirement to propose evidence-based impairment standards is the right step. But standards are only useful if they can be enforced, and enforcement requires reliable detection. The legislation also directs the National Highway Traffic Safety Administration to report on the status of impaired driving prevention technology. This acknowledges that the field is still developing. Unlike a breathalyser, no widely validated, field-deployable device currently exists that can reliably detect cannabis impairment at the roadside with the same precision and legal standing as alcohol testing.

Solving this is not optional. Without a reliable detection tool, impairment standards risk staying aspirational rather than functional. Officers who observe erratic driving behaviour can use standardised field sobriety tests, and some jurisdictions have trained drug recognition experts. These approaches are imperfect and resource-intensive. Policymakers must treat the research and development pipeline for oral fluid testing and behavioural detection technology with the same urgency as any other road safety priority.

Science Must Drive the Standard, Not Lobbying

Beyond detection, lawmakers must set standards that protect road users rather than accommodate frequent users. If the standard is designed around the physiological profiles of heavy cannabis consumers whose THC tolerance makes them appear less impaired than the behavioural data would suggest, it will not protect the people sharing the road with them. The science must drive the standard, not the lobbying.

The standard that protects a frequent user at the expense of a pedestrian is not a safety standard. It is a liability shield.

More Than a Bill Can Do

Legislation creates frameworks. It does not change culture. The BUILD Act, if passed and properly resourced, will establish the measurement systems and standards the United States has been lacking. That is meaningful. It is not sufficient on its own.

Here is what needs to happen alongside it.

Random roadside oral fluid testing must be scaled and standardised. Australia introduced roadside saliva testing for THC in Victoria in 2004. It has since expanded across the nation. Drivers do not need to be observed driving erratically to be tested. The deterrent effect is real, the detection rate is measurable, and the message it sends to the public is unambiguous. The United States has no equivalent national programme. That needs to change, and the BUILD Act’s call for impaired driving prevention technology must be followed by the political will to deploy it.

Driver licensing and renewal must include mandatory cannabis and driving education in every state that has legalised recreational or medical use. Not a checkbox. Not a pamphlet in a dispensary. A tested component of licensing that communicates clearly what cannabis does to reaction time, attention, and hazard perception, and what the legal consequences of impaired driving are. If a state has decided that cannabis is legal to sell, it has accepted a corresponding responsibility to ensure that buyers understand it is not legal to drive on.

Revenue, Warnings and Zero Tolerance

Cannabis tax revenue must fund road safety. Several legalised states collect hundreds of millions of dollars annually from cannabis sales. Governments should direct a mandated proportion of that revenue to public awareness campaigns on impaired driving, drug recognition expert training for law enforcement, and toxicology infrastructure. If governments collect the commercial benefits of legalisation, they must pay the public safety costs of normalisation from the same source.

Point-of-sale warnings on cannabis products must carry the same weight as alcohol warnings, including explicit statements about driving impairment. Currently, dispensary staff are trained to discuss potency and product type. No federal requirement exists compelling them to inform a customer that the product they are purchasing will impair their ability to drive. That is an omission that costs lives.

Authorities must extend and enforce zero tolerance for safety-critical workers without exception. The Department of Transportation’s position this month was correct. Medical authorisation does not neutralise cognitive impairment, and any standard that creates carve-outs for prescribed users in safety-sensitive roles is not a safety standard. It is a legal exposure management strategy dressed up as policy.

The Road Does Not Grade on a Curve

The question of whether a person should drive after using cannabis is not complicated. The answer is no. What has been complicated is the willingness of public institutions to say so plainly while managing the commercial and political interests attached to legalisation. The BUILD Act opens a door. What walks through it will determine whether public institutions treat cannabis and road safety as a genuine public health priority or let the data arrive too late to save the people it was supposed to protect.

The road does not grade on a curve. Neither should the law.

The Dalgarno Institute is an Australian-based research and policy organisation working to strengthen community wellbeing and support healthy development across the lifespan.

Source: marijuanamoment