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#Cars

Autonomous taxis hold the key to reduced greenhouse gas emissions

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With a lot of buzz around autonomous cars, researchers thought of checking out how will such cars perform as far as emissions go and whether they will add onto the already ballooning problem of greenhouse gas emissions or will they help curb them. The answer, it seems, is something that environmentalists would like to hear.

According to an article, published Nature Climate Change, by Lawrence Berkeley National Laboratory (Berkeley Lab), fleet of driverless or autonomous taxis roaming around in cities would both be cost-effective and greatly reduce per-mile emissions of greenhouse gases.

Researchers predict through their analysis that if such a system is put into place, the per-mile greenhouse gas emissions of an electric autonomous taxi in 2030 would be 63 to 82 per cent lower than a 2030 hybrid vehicle driven as a privately owned car and 90 per cent lower than a 2014 gasoline-powered private vehicle.

Jeffery Greenblatt and Samveg Saxena of Berkeley Lab carried out the study and found that of all the variables they had considered, the use of autonomous vehicles as part of a shared transit system seemed to be the most promising one that pointed to lower energy use per mile.

Researchers note that almost half of the savings is attributable to “right-sizing,” where the size of the taxi deployed is tailored to each trip’s occupancy needs. To illustrate the concept, consider a single passenger with no luggage versus a party of four passengers with suitcases. The single passenger would require a much smaller taxi than the party of four, saving money for vehicle owners and passengers. Right-sizing, of course, assumes a fleet of taxis managed by a single entity.

“Most trips in the U.S. are taken singly, meaning one- or two-seat cars would satisfy most trips,” Greenblatt said. “That gives us a factor of two savings, since smaller vehicles means reduced energy use and greenhouse gas emissions.”

Cleaner electric grid is another factor that plays a role in lower emissions for autonomous taxis. Researchers explain that by the year 2030, power plants are expected to be using more renewable energy and emitting less pollution, meaning the greenhouse gas intensity of electricity will be lower.

Being able to employ a range of additional efficiency tactics like driving closely behind other autonomous cars to reduce wind resistance (“platooning”), optimally routing trips, and smoother acceleration and braking, they can further reduce greenhouse gas emissions.

The researchers also conducted an economic analysis to determine how cost-effective autonomous taxis would be. At 12,000 miles per year, the average distance traveled in the U.S. for privately owned cars, electric vehicles in 2030 are still expected to be more expensive than owning and operating a gasoline-powered car, the study found.

But if the vehicle is driven 40,000 to 70,000 miles per year, typical for U.S. taxis, they found that an alternative-fuel vehicle (hydrogen fuel cell or electric battery) was the most cost-effective option. This was based on costs for maintenance, fuel, insurance, and the actual cost of the vehicle (assuming a five-year loan). The reason is that despite the higher cost of a more efficient vehicle, the per-mile cost of fuel is lower, so the savings can pay for the extra investment.

Researchers acknowledge that autonomous taxis are expensive at the moment, but they say that by the year 2030 they will go much cheaper not only because they are efficient, but also because they wouldn’t need a driver.

Researchers further calculated that if just 5 per cent of car sales in 2030 are autonomous taxis, it could help save a whopping 7 million barrels of oil per year and reduce annual greenhouse gas emissions by between 2.1 and 2.4 million metric tons of CO2 per year, equal to the emissions savings from more than 1,000 two-megawatt wind turbines.

Furthermore, the scientists explored the net energy effect of combining ride-sharing with right-sized autonomous taxis. For example, if 10 percent of one-person rides were shifted to two-person rides, the total miles traveled would decrease 3.1 percent while average energy consumption (due to the larger vehicle) would increase 0.6 percent, resulting in a net energy decrease of 2.5 percent.

Greenblatt said plans for further study on this topic are in the works, including exploring the effect of battery degradation, looking at optimal vehicle designs, and making a more realistic simulation of how a fleet of autonomous taxis would actually operate in a metropolitan area.