In professor Kara Kockelman and student Dan Fagnant’s model, one shared autonomous vehicle would take 11 conventional vehicles off the road.
Imagine a world where you wake up in the morning, reserve a car and wait for it to drive itself to your exact location and then pick you up afterward. If you do this on a workday, you could use the commute to prepare for meetings, send emails or work on presentations. And when the car reaches your destination, there is no need to park because it simply moves on to its next passenger.
Would you pay a little extra for the benefits of this “on-demand” convenience?
Civil engineering professor Kara Kockelman and doctoral student Dan Fagnant are betting that many drivers will let go of their existing cars and join shared driverless vehicle fleets to get to and from their destinations.
Kockelman and Fagnant are just two of the researchers at the Cockrell School of Engineering’s Center for Transportation Research who are leading national efforts to study different aspects of autonomous, or driverless, vehicles — everything from security to collision avoidance to environmental impacts. They are helping to prepare for a world where autonomous vehicles (AVs) will become the norm on our streets, said Chandra Bhat, director of the Center for Transportation Research.
The technology that makes driverless vehicles possible is developing at a fast pace, with some experts predicting that luxury AVs will be on roadways by 2020.
To gain a better understanding of how autonomous cars will be integrated into our driving culture, Fagnant and Kockelman set out to model what they refer to as shared autonomous vehicle (SAV) networks, fleets of self-driving cars for which customers pay an initial subscription fee and then pay per use. The researchers were interested in modeling SAVs because of the growth of car-sharing programs like Car2Go and ZipCar, which have gained mainstream popularity and currently have memberships of 140,000 and 850,000 people, respectively. Their work on SAVs was recently published in the journal Transportation Research Part C.
“SAVs could transform transportation for many, especially in large cities where population densities make such SAV systems economically viable,” Kockelman said.
In many large cities, taxi services provide a similar service to consumers, but the benefits of shared autonomous vehicles are clear: safety, cost and convenience. Unlike conventional taxis, SAVs will be outfitted with collision avoidance systems that take action without driver input by moderating speed and steering, to keep all roadway users safer. Labor costs will also be lower for SAVs than for taxis, since no paid drivers are needed.
“The cars could find us quickly and efficiently, and we wouldn’t have to worry about parking,” Kockelman said. “And even if I’m in a conventional car, I’m made safer by the connected and autonomous cars on the road.”
The sticker price on AVs will decrease over time, but the vehicles are expected to have extra costs associated with maintaining and upgrading the technology. Since SAVs will be used much more heavily and therefore have a greater turnover rate, consumers of shared vehicles would be incurring far less of those costs, making SAVs more attractive to all travelers, Fagnant said.
The Austin Model
Using advanced computing, Kockelman and Fagnant modeled hundreds of daylong SAV passenger pick-up and drop-off scenarios within a 10-by-10-mile radius. Austin’s general population and density patterns served as the model’s baseline. Their model had SAVs representing 5 percent of all trips made by a total population of approximately 20,000 people.
The researchers concluded that this group of 20,000 people, who were previously served by roughly the same number of conventional cars, would now be served by only 1,700 SAVs. That means that one SAV would take 11 conventional vehicles off the road, freeing up just as many parking spaces in the process.
Kockelman and Fagnant also estimated an average wait time under 20 seconds — from the time trip-makers arrive at a shared-car station or parking area to the time their cars are available — and found that fewer than 1 percent of SAV members would have to wait more than five minutes. Additionally, each SAV would be responsible for emissions savings, including 34 percent less carbon monoxide emissions, largely due to fewer cold engine starts, which are a major source of emissions.
The researchers did spot disadvantages, however, including the possibility that SAVs would lead to more traffic congestion, even as they are taking conventional vehicles off the road.
“All vehicles that are automated and connected have an opportunity to cut congestion, particularly on freeways, through processes like cooperative adaptive cruise controls,” Fagnant said. “But at lower levels of market penetration, SAVs may actually lead to more congestion, since each vehicle will be traveling unoccupied as it drives from one passenger to the next.”
In the not-so-distant future, Fagnant believes that his and Kockelman’s SAV model could help drivers, urban planners and policymakers make better transportation decisions, and facilitate ride-sharing, which can moderate possible congestion impacts emerging from easier travel.
“I think city planners would be very interested in the parking implications,” Fagnant said. “And cities could potentially operate their own fleets of SAVs, not just for single occupancy but also for ride sharing.”
Fagnant and Kockelman are now applying local land use, network and travel data to reflect Austin-specific travel patterns. Their new model is designed to test the implications of using SAVS to ride share, whereby travelers headed to the same destination or in similar directions can share a ride in a single vehicle.
Vehicle icon in top illustration courtesy of Oliver Guin, through Creative Commons.
