Drink driving and self-driving cars

Mr Bean on top of a Mini
Mr Bean's home made self-driving (sort of) car

Because I run London Drink Driving Solicitor and people like to be clever, I am occasionally asked what the legal position is should self-driving cars be released for sale vis-à-vis drink driving.  I assume that a lot of people would like to be able to go out, get drunk and then travel home in their own car without putting themselves or anybody else in danger – nice thought, I like the idea too.

What’s the legal position?

First, section 5 of the Road Traffic Act 1988 says that a person who drives or attempts to drive a motor vehicle on a road or other public place while the alcohol in the breath, blood or urine exceeds the drink driving limit commits an offence.  It also goes on to say that anybody who is in charge of a motor vehicle with alcohol above the drink driving limit commits an offence.  So, we have two offences, drink driving and being in charge.

For the purposes of this exercise we’ll assume that Tina is alone in a self-driving car that is moving under the control of its own computer on a road that is open to the public and that Tina is significantly above the drink driving limit.  Now we’ve made those assumptions, we need to ask ourselves three questions:
1.       Is a self-driving car a motor vehicle for the purposes of the Road Traffic Act 1988?
2.       Is Tina driving it?
3.       Is Tina in charge of it?

Is a self-driving car a motor vehicle?

Yes, obviously it is… or shall we apply some law and think about it more carefully?  Okay, we’ll do the boring thing and think about the law.

Section 185(a) of the Road Traffic Act 1988 defines a motor vehicle thus:

“’motor vehicle’ means…  a mechanically propelled vehicle intended or adapted for use on roads.”

Well that looks pretty clear cut – I suppose we should probably look at whether there are any exceptions to this.  I mean a lawnmower could be intended for use on the road cutting the grass verge so let’s take a look at the exceptions.  There are a few, but the most potentially relevant is section 189 of the RTA 1988.  That actually includes an exception for lawnmowers – see I told you! – but more interesting is subsection (1)(b), which says “any other mechanically propelled vehicle controlled by a pedestrian which may be specified by regulations made by the Secretary of State for the purposes of this section and section 140 of the Road Traffic Regulation Act 1984”.  This is interesting because subsection (2)(b) says that “controlled by a pedestrian” means a vehicle that “… is constructed or adapted for use either under such control or under the control of a person carried on it, but is not for the time being in use under, or proceeding under, the control of a person carried on it.”  Weird as it sounds, “controlled by a pedestrian” does not appear to require a pedestrian to actually be controlling the vehicle provided it is not being controlled by the occupant.  This is probably because the RTA was drafted in the early 1980s and Parliament never considered self-driving cars.

Anyway, the Secretary of State has the power to issue regulations that prevents motor vehicles being treated as motor vehicles for the purposes of the Road Traffic Act.  Currently, it appears no such regulations have been made, but this section would give the Secretary of State the power to exclude self-driving cars from drink driving laws at a stroke.

Currently then, a self-driving car is a motor vehicle for the purposes of drink driving law.  There was me thinking I was going to be able to wrap this up quickly.

Is Tina driving?

I am not going to bore you with a rendition of the all the authorities on “driving” suffice to say that a driver need not be in the driving seat (Tyler v Whatmore).  Driving should be given its ordinary English meaning and requires a person to have a degree of control sufficient to amount to driving in the ordinary sense of the word (Jones v Pratt).  Somebody who momentarily grabs the wheel, steering the car off the road is not driving (also Jones v Pratt).  A driving instructor who has controls that allow him to take control of the vehicle may be a driver even if he is not in the driving seat (Langman v Valentine)

In R v MacDonagh, the then Lord Chief Justice, Lord Widgery said this:

1.       “The primary consideration as to whether a person is “driving” is essentially a question of fact, dependent on the degree and extent to which the person has control of the direction and movement of the vehicle.”
2.       “One test is whether the accused was “in a substantial sense controlling the movement and direction of the car” (Ames v MacLeod, [a Scottish case]). A person cannot be said to be “driving” unless he satisfies this test.”
3.       “The fact that a person satisfies the test of control in Ames v MacLeod is not necessarily exhaustive. It has still to be considered whether the activity in question could fall within the ordinary meaning of the word “driving” in the English language.”

Burgoyne v Phillips added some extra points:

4.       “The essence of driving is the use of the driver’s control in order to direct the movement of the vehicle however the movement is produced.”
5.       “Whether the defendant himself deliberately sets the vehicle in motion is an important factor.”

In our case a lot will come down to the design and operation of our self-driving car.  If Tina is expected to intervene in an emergency we may get a different result to a situation where she is unable to assume direct driving control of the vehicle at all.

Would sitting in a self-driving car “fall within the ordinary meaning of the word ‘driving’?”  I think not.  Given the car is driving itself, Tina is not controlling the direction or movement of the vehicle, although it is likely that her actions would set the vehicle in motion.

My personal view is that it is unlikely Tina would meet the definition of a driver in a self-driving vehicle.  Although, if the design allows her to take control in an emergency then she may be driving in the same way the driving instructor sat in the passenger seat was a driver in Langman.

Is Tina in charge?

“In charge” is not defined by the RTA 1988 but it was considered in DPP v Watkins where the court said that each case will come down to its own facts but generally courts should consider the following issues:

1.       whether and where he was in the vehicle or how far he was from it;
2.       what he was doing at the relevant time;
3.       whether he was in possession of a key that fitted the ignition;
4.       whether there was evidence of an intention to take or assert control of the car by driving or otherwise;
5.       whether any person was in, at or near the vehicle and, if so, the like particulars in respect of that person.

In our case, Tina is inside the car.  At the relevant time she is travelling, albeit she could be asleep, reading a book or having some more drinks.  We can assume she is in possession of the “key” otherwise we assume the car wouldn’t be driving her home.  We can assume nobody else is in the car.
Tina doing her make up behind the wheel of her car
Ahh Tina is doing her make-up

Point 4 is the most relevant, I think, because it again comes down to the design of the car.  If there is no possibility of Tina controlling the car’s steering, speed, etc then we must say there is no evidence of her intending to take or assert control.  But, if she might be required to take control in an emergency then we would have to conclude that there is such evidence.

Statutory defence

Section 5(2) RTA 1988 provides a defence to being drunk in charge where there is no likelihood of somebody driving while they remain above the drink driving limit.  Again, if Tina might be required to assume control then she cannot afford herself of this defence.  But, if the design of the car offers her no opportunity to control it then she can rely on this defence.


We can see that a lot will rest on the design of the self-driving car.  If it is a moving living room with no way of controlling the driving other than to tell the car where you’d like to go then it is difficult to see how somebody could be defined as a driver.  It would be easier for the person to be convicted of an offence if the design of the vehicle gives them more control but it will depend very much on the facts in each case.

We have looked at what happens if there is one person in the car all by herself, but the situation will be much more complex if there happens to be more than one occupant.

There appears to exist a power that could be used by the Secretary of State to exempt the occupants of self-driving cars from driving offences, although it has to be said it is unlikely that is a use Parliament ever intended when the law was passed.


  1. My grandfather-in-law would routinely have a skinful at a local pub before being taken home in his self-driving vehicle, which was a horse and cart. the horse knew its way home.

    I wonder if there is any old caselaw about horses that would shed some light on the self-driving car thing.

    1. Your grandfather-in-law was a very naughty boy who was certainly committing an offence under section 12 of the Licensing Act 1872, which prohibits being in charge of a horse while drunk.

  2. I think you can be drunk in charge of a horse, or of a child for that matter.


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