Robots used for delivery, maintenance, surveillance or other tasks within public areas are collectively known as public-area mobile robots or PMRs.
One of the most important safety aspects of deploying PMRs is their behaviour as they mix with pedestrian, cyclist, and motor-vehicle traffic. And the most critical safety component occurs when a PMR crosses a roadway.
Here, we consider PMRs crossing roadways at crosswalks and traffic intersections with pedestrian signals. As an aside, it is our advice that it should be made illegal for a PMR to cross a motor vehicle roadway in the case of the absence or malfunction of a traffic signal that would otherwise have been set up for pedestrians.
PMRs are expected to follow the same rules as pedestrians in many jurisdictions, whether by default or regulation. As well, motor vehicle drivers are to treat PMR rights-of-way as they are to treat those for pedestrians. In other words, PMRs are to behave as, and be treated as, pedestrians. This does not make PMRs equivalent to pedestrians, as is sometimes misstated. PMRs are mechanical devices, not humans. Some have a modicum of software-based navigational intelligence; humans remotely teleoperate the others. None are conscious, aware, or responsible; at this time, only their fleet operators and teleoperators are.
As cities or towns consider permitting or acquiring PMRs for delivery, maintenance or surveillance tasks, they are responsible for ascertaining that these robots behave safely at traffic intersections.
“Behaving safely” means several things:
Robots must obey traffic signals in the same ways as are intended for pedestrians
Robot behaviour at intersections must be consistent — i.e., all robots should behave according to the same rules in all road-crossing circumstances
Robot behaviour must be transparent to nearby pedestrians to avoid alarm or confusion to such bystanders.
Waiting for signals
A PMR entering a road crossing must be able to complete the crossing while the relevant traffic signals indicate that pedestrians have the right of way.
The common human pedestrian practice of entering a road crossing toward the end of the signal countdown or even as a walk signal changes to “Don’t Walk” or the automotive traffic signal changes to amber must be made an illegal PMR behaviour.
This has already been known to happen for teleoperated PMRs. This should not be surprising, as they are being teleoperated by humans who tend to exhibit the same shortcut behaviours as pedestrians.
Also, turning back mid-crossing must be made illegal, except in extreme circumstances.
There are three fundamentally distinct ways for a PMR to ensure it has sufficient time to complete a road crossing:
Wait at the side of the curb ramp for a fresh walk signal
Use and obey “connected vehicle” signal systems intended for automated vehicles, of which PMRs are an instance. At least one traffic integrator operating in the EU has addressed this.
Rely on a human teleoperator to understand enough about the crossing infrastructure, the length of signal time remaining for a pedestrian to cross (at the PMR’s legally permitted speed), and the current (real-time) density of pedestrian traffic (navigation impedance) to determine whether to begin crossing the roadway. This third approach requires sufficient sensory capabilities on the robot for its onboard navigation systems or its teleoperator to execute appropriate forward-planning (see draft ISO 4448). In the case of teleoperation, it also requires close human attention to make the correct judgment and maneuver. The PMR’s fleet operator must also assume responsibility in this matter.
Because traffic at road crossings includes humans—automobiles, bicycles, pedestrians, and wheelchairs—concurrently competing to navigate this space, there will always be a degree of uncertainty embedded in any of these three approaches. Draft technical standard ISO 4448 introduces considerably more detail about the multiple steps necessary on the part of a more fully automated robot.
Road crossings include emergency vehicles—EMS, fire, or police—passing through while using systems of emergency sounds and lights to warn all other users to stay clear during their passage.
There must be a well-documented and tested system for each PMR fleet—whether automated or teleoperated—to clear and remain clear of road crossings in the event of such a warning from an emergency service vehicle.
Draft ISO 4448 deals with this in far more detail.
We recommend that any jurisdiction permitting PMRs to cross roadways—regardless of the level of automation declared by their manufacturer or fleet operator—have these tested for road-crossing safety. This includes:
Independent, third-party testing for safe road-crossing behaviour
Independent, third-party assessment of the teleoperator training guide regarding road-crossing as provided by the PMR fleet operator to its teleoperation team
Documented assurance that the fleet operator and/or the jurisdiction carries sufficient insurance against harm due to PMR errors or crashes.
All of the above should be overseen and closely inspected by the appropriate authority licensing these devices.