Electric bus maker Proterra is investigating autonomous-driving tech, including fully autonomous buses. But many of the scenarios proposed by Proterra CEO Ryan Popple in a blog post still keep human drivers in the loop.

Future buses may only drive themselves in certain situations, Popple said. Buses could move autonomously around depots, driving in and out of parking spaces and pulling up to charging stations without human drivers, he said. This could maximize the use of space since buses could be parked very close together, according to Popple. Automakers have made similar claims for proposed autonomous-parking systems, and Tesla drivers can already use Summon to maneuver their cars in and out of spaces too tight to open and close the doors.

A second scenario discussed by Popple is "platooning." This would involve a lead bus with a human driver followed closely by other buses operating in autonomous mode. Autonomous buses could drive in a tight formation safely, Popple said, reducing aerodynamic drag and increasing efficiency. Transit operators could use platooning to increase capacity on a given route, Popple said, without having to add another driver. He also suggested that platooning could work well in bus rapid transit services. Often pitched as an alternative of commuter trains or light rail, this places buses on a dedicated right of way, allowing them to avoid other traffic.

Platooning has been discussed for both self-driving cars and commercial trucks; the first tests were conducted in the 1990s. The concept promises better aerodynamic and space efficiency on highways, but is likely better suited to buses and commercial trucks that travel on predictable routes. That creates opportunities for platooning that are less common with passenger cars.

Fully autonomous buses are also a possibility, Popple said. But they may be difficult to develop. In addition to driving themselves, buses without a human operator will need to take on tasks like fare collection, assisting the elderly and disabled, and helping passengers navigate to their destinations, Popple noted.

Before they go fully autonomous, buses could also gain the driver-assist features that are already commonplace in passenger cars and are making their way into commercial trucks. Bus drivers already have a challenging job, Popple noted. Features like autonomous emergency braking, or a precision-maneuvering system for narrow lanes, could take some of the workloads from the driver without completely automating the vehicle. Drivers of passenger cars sometimes overestimate the capabilities of driver aids, so the challenge here would be ensuring that bus drivers are properly trained in the limitations of these systems.

Proterra launched an autonomous-bus development program in 2017, based in Reno, Nevada. The company is working with the University of Nevada, Reno and the Regional Transportation Commission of Washoe County, the local public-transit operator. On the other side of the world, Volvo will test a pair of autonomous electric buses in Singapore. These efforts show that autonomous-driving tech is not limited to passenger cars.