How will the police pull over a driverless car? (Photo: Adobe Stock / Mark Poprocki)

Driverless cars: stop in the name of the law!

Safety and Ethics

Prof. Jutta Stender-Vorwachs & Hans Steege

Prof. Jutta Stender-Vorwachs & Hans Steege



In the second instalment of our new legal series, our experts from the University of Hanover are back to discuss what autonomous vehicles might mean for law enforcement. Who actually stops an autonomous vehicle on the run?

Life might be easier and safer with autonomous driving. Because with it comes new mobility concepts, not least, the so-called shared economy,breaking what is currently a clearly defined ownership culture. On top of that, while being driven (by the autonomous system), car passengers get the opportunity to use the travel time as they please. Whether that be working, surfing the Internet or even sleeping – fully autonomous vehicles will not be dependent on the driver. So much so that they could also be on their way without any passengers: a loaded truck, for instance, or an autonomous car dropping the passenger off at work then looking for a parking lot or the next passenger.


Indeed, with the advent of autonomous cars, many tasks will turn out to be easier than ever before: many…but not all. One area that faces a huge upheaval is law enforcement. How do the police pull over a driverless car? What does autonomous driving require from a legal point of view with regard to police officers and police inspections?




Provided there are passengers onboard an autonomous vehicle, things remain relatively simple. They recognize the usual police signals such as flashing blue lights or sirens and then react accordingly. No matter under which jurisdiction, passengers must bring the autonomous vehicle to a standstill in such a case. This is possible without any problem. If the passenger on the other hand refuses to obey the command to stop, then they bear the brunt of any subsequent sanctions - just as the prior command to stop was directed at him/her.


Legally – as well as technically – it becomes interesting if and when the police want to stop an autonomous vehicle without any passengers on board, or one whose occupants are sleeping or indeed blind or deaf – not to mention small children, i.e. those who cannot react to the signals and instructions given by the police.

Humans recognize flashing blue lights. But what about machines? (Photo: Adobe Stock / Артем Константинов)

It is clear that autonomous vehicles must also be subject to and accessible for controls on the part of state authorities. But the nature of those controls may not be as we know them now. In the future, it will not be a case of controlling erratic driving or the consumption of alcohol but rather primarily the freight of autonomous vehicles. Even now, criminals use vehicles as weapons – like in the attack in Barcelona on 17th August 2017, Berlin at the Christmas fair on 19th December 2016 or Nice on 14th July 2016.


If not the car per se, then its cargo space or trunk could also be used to carry weapons, explosive material, smuggled goods or even trade in human beings.


If it is not permissible in law for police officers to bring an autonomous vehicle to a halt, then they constitute an area not regulated by law where police inspections are not possible.




As long as there are passengers in an autonomous vehicle and you are appealing to the human senses, then optic and acoustic signals can be considered – because passengers can react to them.


Yet if such an attempt comes to nothing because passengers either don’t react or there are no passengers on board, then car-2-car communication between the police car and the autonomous vehicle in question could provide just the right solution. However, granting police cars the access to take over the steering and control any autonomous vehicle poses immense security risks – especially in times of heightened risk of hacker attacks. In such a concept, it is imaginable that cybercriminals could stop an autonomous vehicle rather easily, with grave consequences for both the passengers and the freight.


Implementing an authentication system would be technically safer. But would such a system be legally possible? This will be illustrated using German law.




As autonomous vehicles will also be connected, it is possible to bring the OEM into the police inspection process and to interconnect them as a check in the technical process. Under the German legal system, the OEM would act as an administrative assistant and only carry out acts without possessing any discretionary power. This prevents the risk of misuse.

Will cybercriminals be able to remotely control an autonomous vehicle? (Photo: Adobe Stock /

Due to safety considerations, such a communication should be via satellite, not via mobile network as coverage cannot be guaranteed everywhere. Using such an authentication system would require the police authorities as well as the OEM to operate over a server. At first, every OEM would get an authentication key for every police vehicle on duty. If a police officer should want to stop a vehicle, an encrypted message would be sent to the server of the OEM by the police vehicle. The OEM would then compare that key with the original. Thereupon the OEM sends an inquiry to the server of the police authorities and requests the key used. If the police server confirms that it is a vehicle on duty, the OEM could then access the autonomous vehicle remotely, thus overriding the driving process and bringing the vehicle to a stop.


Such an authentication system would be a tough, real-time system fast enough for practical application.



Nevertheless, there is a remaining risk with regard to hacker attacks concerning each interface. Owners of autonomous vehicles are, legally speaking, not completely unprotected. If the safety mechanisms used by the police authority or the OEM fail, the damaged vehicle owner could claim for damages against either party - depending on the jurisdiction.


On a national level, according to German law, the authority may be held liable for damages as per § 839 BGB (German Civil Code) combined with Art. 34 S. 1 GG (German Constitution). However, this obviously requires that the authority actually is at fault.


However, on a state level, the federal state police law does not require any fault by the authority in order to consider a claim against them. To achieve the aim that owners of autonomous vehicles are protected across the whole country, all states must regulate a claim irrespective of where fault lies in such situations.


In the event of a breach of its responsibilities, the OEM could be claimed against for compensation according to the German Civil Code.


To summarize, while not without challenges, police inspections of autonomous vehicles are certainly technically as well as legally feasible in future.



More information on this topic can be found in Stender-Vorwachs/Steege,Neue Zeitschrift für Verkehrsrecht, 12/2017, 553-556.

Written by Prof. Dr. iur. habil. Jutta Stender-Vorwachs and Hans Steege, both members of the Faculty of Law of the Leibniz University Hannover and the Interdisziplinäres Institut fürAutomatisierte Systeme e.V. (RifaS).


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