The Law Commission of England and Wales and the Scottish Law Commission said, though, that a digital highway code would be "extremely difficult to produce, given the complexity of the driving rule book and the huge variety of implicit interpretations and exceptions".
The Commissions addressed the subject of a digital highway code in a new consultation paper – the first of a series of such papers they have promised during a three-year long review they are carrying out into the laws and regulations needed to support the introduction of autonomous vehicles in the UK.
The concept of a digital highway code was endorsed in a recent paper by software company FiveAI. It said there is a need for "a publicly-available, machine-readable and complete set of … traffic laws and driving codes and conventions" to promote the safety of automated driving systems.
FiveAI said a digital highway code must give account to "when and how exactly can a vehicle cross a centre dividing line, if present, to avoid a lane obstruction; when would it be acceptable to mount a sidewalk; what should a driver be permitted to do if traffic lights are defective and so on". It said it should also govern when autonomous vehicles should let other road users merge into the lane it is in and determine the extent to which those vehicles "have a responsibility to ensure the most efficient use of the road network".
However, in their paper, the Commission said that "a digital map of road rules" is not enough on its own to regulate how driverless cars should operate. Instead, "unprecedented" collaboration between policymakers and developers is needed to formalise 'exception-handling rules' which it said are "currently implicit in 'common sense' driver behaviour, personal value judgements and prosecutorial discretion".
In their consultation, which is open until 8 February 2019, the Commissions asked stakeholders for their views on when they think an automated vehicle should be allowed to mount the pavement, exceed the speed limit or edge through pedestrians. They said they have no "preconceived ideas on these issues".
The Commissions posed further questions on a broad range of other legal issues, including potential new criminal penalties for developers of automated driving systems whose "wrongs" result in death or serious injury.
The questions also touch on cybersecurity risks and the potential for new laws in that area, and ask whether there is a need to modify criminal and civil liability laws to clarify who is accountable if things go wrong with the way the vehicles operate. The UK has already legislated in this area with the Automated and Electric Vehicle Act.
In its paper, the Commissions said that while it is "not possible to specify hard and fast rules about when automated driving systems can operate safely and effectively" when not controlled by humans, it "tentatively" proposed that "new and flexible powers" be introduced to enable truly autonomous vehicles to operate.
In one example they outlined what could be done to support private ownership of fully autonomous vehicles.
"One possibility might be to require owners to contract with a service provider who would perform some of the same functions as licensed operators [which the Commissions suggested could operate to support mobility-as-a-service solutions]," the Commissions said.
"For example, the service provider could ensure that vehicles are properly maintained and updated and could issue targeted weather warnings to ensure the operational design domain is not exceeded. A service provider could also supervise empty vehicles remotely and provide speedy break-down services to tow vehicles that have stopped," they said.
The Commissions also suggested a new "safety assurance scheme" could be established "to authorise automated driving systems which are installed either as modifications to registered vehicles or in vehicles manufactured in limited numbers".
The scheme could be overseen by an existing body like the Vehicle Certification Agency or the Driver and Vehicle Standards Agency or by a new safety assurance agency, it said.
The Commissions also suggested a new specialist 'Accident Investigation Branch' could be set up to scrutinise accidents involving autonomous vehicles. It said such a unit "could develop high levels of technical expertise and pool data over many individual incidents" and "would aim to understand the causes of an accident, rather than ascribe blame".
"The introduction of driving automation raises new challenges for the current system of investigating road accidents," the Commissions said. "If these systems malfunction, they are likely to do so in ways which are unfamiliar to coroners or police officers. Understanding the causes of such failure will involve new types of expertise. We seek views on how these challenges could be met."
"One possibility might be to consider an Accident Investigation Branch, similar to the NTSB in the United States, to investigate high profile road accidents which raise general safety issues. Such a branch might be able to develop particular expertise in driving automation. An alternative approach would be to maintain the current system of police and coroners’ investigations, but to provide investigators with new resources to draw on," it said.
Ben Gardner, expert in autonomous vehicles technology and regulation at Pinsent Masons, the law firm behind Out-Law.com, said: "The transport sector is likely to go through more change in the next five to 10 years than it has in the last 50 and, as we try to introduce these changes against the backdrop of the UK's existing regulatory frameworks, there will inevitably be obstacles, incompatibilities and grey areas."
"These will need to be addressed in two ways: through introducing new rules and regulations to legislate for future vehicles and use cases; and amending or removing old legislation which is not fit for purpose in the modern day," he said.
Gardner said that the Commissions' consultation poses interesting early thoughts and questions, and demonstrates that there is "no clear cut approach" which the government is looking to adopt.
"Importantly, the consultation gives those with an interest in the sector to influence what the future might look like," Gardner said.
"One thing which will be important going forward will be to try and make the law as agile as possible so that any legal obstacles or uncertainties can be dealt with swiftly, but also appropriately. Seeking to avoid stifling innovation whilst as the same time maintaining safety and the functioning of the road network will be an issue that the government will need to constantly wrestle with over the coming months and years if it is to put the UK at the forefront of autonomous vehicle development globally," he said.