Berkeley Lab analysis finds autonomous electric taxis could greatly reduce US LDV GHG emissions
06 July 2015
Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) have found that the per-mile greenhouse gas emissions of an electric autonomous taxi in 2030 would be 63-82% lower than a projected 2030 hybrid vehicle driven as a privately owned car and 90% lower than a 2014 gasoline-powered private vehicle. Their paper appears in the journal Nature Climate Change.
The autonomous vehicles (AVs) gain their through three synergistic effects, the researchers found: (1) future decreases in electricity GHG emissions intensity; (2) smaller vehicle sizes resulting from trip-specific autonomous taxi deployment (i.e., “right-sizing,” where the size of the taxi deployed is tailored to each trip’s occupancy needs); and (3) higher annual vehicle-miles travelled (VMT), increasing high-efficiency (especially battery-electric) vehicle cost-effectiveness.
|
|
| Greenhouse gas (GHG) emissions intensities per mile for conventionally driven vehicles (CDVs) in 2014 and 2030, and autonomous taxis (ATs) in 2030. Cost-optimal vehicle technologies indicated by asterisks: ICEV, internal combustion engine vehicle; HEV, hybrid-electric vehicle; BEV, battery-electric vehicle. Greenblatt & Saxena (2015). Click to enlarge. |
The substantial GHG savings could enable GHG reductions even if total vehicle miles traveled (VMT), average speed and vehicle size increased substantially, Berkeley Lab scientists Jeffery Greenblatt and Samveg Saxena suggested. Oil consumption would also be reduced by nearly 100%.
When we first started looking at autonomous vehicles, we found that, of all the variables we could consider, the use of autonomous vehicles as part of a shared transit system seemed to be the biggest lever that pointed to lower energy use per mile.
—Jeffery Greenblatt
Many automakers and other companies are working on autonomous cars. Right-sizing is cost-effective for both the fleet owner and for passengers, and small one- and two-seat vehicles are being explored by researchers and companies. As an example, a single passenger with no luggage would require a much smaller taxi than a party of four with luggage. Right-sizing assumes a fleet of taxis managed by a single entity.
Most trips in the US 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.”
From another perspective, if 10% of one-person rides were shifted to two-person rides, the total miles traveled would decrease 3.1% while average energy consumption (due to the larger vehicle) would increase 0.6%, resulting in a net energy decrease of 2.5%.
Self-driving cars have additional efficiencies that have been covered in other research, such as the ability to drive closely behind other autonomous cars to reduce wind resistance (“platooning”); optimally routing trip;, and smoother acceleration and braking. Greenblatt and Saxena, however, did not include these incremental effects in their baseline results.
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 US 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 US 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.
An autonomous taxi using today’s technology would still be cheaper than an ordinary taxi not simply due to its greater energy efficiency, but also due to the fact that no operator would be required. By 2030, autonomous taxis could be far cheaper than their driven counterparts.
Greenblatt and Saxena did not try to estimate how widespread this technology would be in 2030. However, they did calculate that if five percent of 2030 vehicle sales (about 800,000 vehicles) were shifted to autonomous taxis, it would save about 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.
To estimate the number of trips taken by different numbers of occupants, the researchers analyzed National Household Travel Survey data from the Federal Highway Administration. The scientists then modeled hypothetical one- and two-seat vehicles based on Nissan Leaf parameters driving three test-drive cycles as defined by the Environmental Protection Agency (EPA) using Autonomie, a vehicle-modeling tool developed by Argonne National Laboratory that simulates energy consumption on a second-by-second basis.
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.
The study was funded in part by the Laboratory Directed Research and Development (LDRD) program at Berkeley Lab.
Resources
Jeffery B. Greenblatt & Samveg Saxena (2015) “Autonomous taxis could greatly reduce greenhouse-gas emissions of US light-duty vehicles” Nature Climate Change doi: 10.1038/nclimate2685
Very interesting to finally quantify the impact of right-sizing vehicles.
I wonder, though, if people shift to paying for travel on a per-trip basis with autonomous taxis (as opposed to purchasing a vehicle) how that will impact their travel behavior, likelihood of carpooling, and annual miles traveled. Seems like we should expect VMT reductions and greater carpooling in addition to the benefits enumerated in this study.
The real wild cards with autonomous vehicles are their impact on travel behavior and residential location choices. Maybe DOE can study that in the future as well.
Posted by: GM | 06 July 2015 at 06:46 PM
It might take a change in attitude for people to turn up in tiny one man "unipods" or smart car like "duopods".
I suppose if they were definitely cheaper, or faster (able to use narrower lanes) people would use them, as long as 4 seat "conventional" sized cars were available for those who couldn't show up in a unipod.
Imagine an automatic driving motorbike! (You might need a little extra deodorant).
Posted by: mahonj | 07 July 2015 at 12:24 AM
As shown below the economics of self-driving BEVs is much better than traditional gassers or self-driving grassers. Note those calculations are not assuming any benefits for BEV "right sizing". Allowing for that will bring the transportation cost further down.
Specifically, an autonomous BEV taxi will cost you 0.16 USD per mile to drive. A self-owned Camry gasser will cost you 0.41 USD per mile or about 500 USD per month if you drive 15,000 miles per year (= ($0.41*15,000/12). Finally, a human operated taxi Camry will cost you 1.41 USD per mile which is representative of actual taxi rates.
Reducing the cost of taxi driving from 1.41 USD to 0.16 USD per mile using an autonomous BEV taxi is simply revolutionary. The world will change for the better as a result. Far fewer traffic accidents, no air pollution from land transportation, no import of oil for making transportation fuels, no wasted time by traffic congestion. Time spend for transportation can be used productively to sleep, eat, work or for entertainment or education. The average American household can reduce transportation expenses from 500 USD per month per car needed in household to 200 USD per car (= ($0.16*15,000/12). This is as big as it gets for the automotive industry and it will change the world for the better.
Documentation for costs to drive one mile:
1) Life cost to own Toyota Camry: 65,133 USD = (23,000 USD for Camry + 16,000 USD for life gasoline + 4,800 USD for life maintenance + 21,333 USD for life car insurance).
Life cost per mile: 0.41 USD = $65,133/160,000 miles service life.
2) Life cost of Toyota Camry with human taxi driver: 225,133 USD = (23,000 USD for Camry + 16,000 USD for life gasoline + 4,800 USD for life maintenance + 21,333 USD for life car insurance + 160,000 USD for taxi driver).
Life cost per mile: 1.41 USD = $225,133 /160,000 miles service life.
Now consider a fully autonomous taxi with an ultra durable 24kwh lithium titanate battery (10,000 cycles) giving it about 85 miles of range and a service life of 850,000 miles. With autonomous driving the range issue and charging time issue no longer exists as you can change the vehicle in seconds to go an additional 85 miles and keep doing it until you reach your destination. This is the BEV conception that will wipe out any gasser on the market because its total cost per mile is unbeatable by any gasser.
3) Life cost of autonomous BEV taxi: 133,467 USD = (35,000 USD for BEV taxi + 28,800 USD for life electricity + 17,000 USD for life maintenance + 56,667 USD for life car insurance - 4000 USD scrap value of battery).
Life cost per mile: 0.16 USD = $133,467/850,000 miles service life.
------
Add 1) Toyota Camry assumptions: 1) Service life is 160,000 miles. 2) Long-term price of gasoline is 3 USD. 3) It gets 30 mpg so 16,000 USD spend on gasoline = (160,000/30)*$3. 4) Maintenance cost for oil change, tires, brakes, coolant, etc is 300 USD per 10,000 miles so 4,800 USD = (160,000/10,000)*300 USD. 5) Insurance cost is 2000 USD per 15000 miles so life car insurance is 21,333 USD = (160,000/15,000)*$2000.
Add 2) Toyota Camry taxi assumptions: 1) Service life is 160,000 miles. 2) Long-term price of gasoline is 3 USD. 3) It gets 30 mpg so 16,000 USD spend on gasoline = (160,000/30)*$3. 4) Maintenance cost for oil change, tires, brakes, coolant, etc is 300 USD per 10,000 miles so 4,800 USD = (160,000/10,000)*300 USD. 5) Insurance cost is 2000 USD per 15000 miles so life car insurance is 21,333 USD = (160,000/15,000)*$2000. 6) Hourly pay to chauffeur is 20 USD and hourly markup for time wasted and taxi company overhead is another 20 USD. Operating hours in service for life of car assuming 40 mph is 4000 hours =(160,000/40) so total life cost of chauffeur and taxi company overhead is 160,000 USD = (4000*($20+$20)).
Add 3) Fully autonomous BEV taxi assumptions: 1) Service life is 850,000 miles (= 85 miles battery range*10,000 deep cycles) which corresponds favorably to warranty for Toshibas lithium titanate batteries (see http://www.scib.jp/en/product/detail.htm). 2) 0.28kwh is used to drive one mile (=24kwh battery/85miles range), 3) electricity cost is 28,800 USD = (12 cents per kwh * 0.28kwh* 850,000 miles) which could be much lower off peak, 4) maintenance cost for tires, brakes, coolant, etc is 200 USD per 10,000 miles so 17,000 USD = (850,000/10,000)*200 USD, 5) scrap value of battery after 850,000 miles is 4000 USD. 6) Insurance cost is 1000 USD per 15000 miles so life car insurance is 56,667 USD = (850,000/15,000)*$1000. The lower car insurance for autonomous vehicles assumes that they are twice as good as human drivers to avoid accidents. 7) The Leaf sized vehicle costs 35,000 USD with a 24kwh battery. It is assumed 12000 USD (=24kwh*$500) can be attributed to the battery pack, 6,000 USD for autonomous technology (computers, sensors and redundancy of critical systems) and 17,000 USD for other car expenses. All costs are including gross margins.
Posted by: Account Deleted | 07 July 2015 at 01:18 AM
Change in behavior may depend on overall system capability. If I can take an autonomous taxi, BEV or not, from home to the light rail, then from light rail to work, and back, I might pay the $.16 per mile. But I don't think I will be quick to change to an autonomous taxi for the full trip. My personal vehicle, expensive as it is, seems more convenient.
Also, I don't see the direct costs of my vehicle every day, where I do for the taxi. I think this "visible" charge is one reason many people do not change to public transportation. They just are not aware of the cost of driving.
Posted by: JMartin | 07 July 2015 at 07:53 AM
Let'S do it and include UBER cąrs and all city buses, specially the electrified units.
Posted by: HarveyD | 10 July 2015 at 08:10 AM