|Fig. 1: Example of Self Driving Car. (Source: Wikimedia Commons)|
Lightweight vehicles are a major energy consumer world-wide. In 2014 the global power budget for all forms of energy was approximately 15 Terawatts.  The majority of this power was consumed in electricity production for homes and commercial use but there were also over one billion operating light weight vehicles on the road.  These cars consume nearly 0.5 Terawatts or approximately 3% of the world's energy budget. 
The majority of cars burn fossil fuels but our dependence on fossil fuels needs to be curbed since they are a limited resource and their consumption contributes to global warming. [1,4] Our global energy consumption can be made more efficient and green by changing the fuel used by cars and how they are operated on the road. The advent of autonomous vehicles can be used to reduce our overall energy budget by driving in an optimally minimal path, employing fuel-efficient driving habits, and using inexpensive renewable fuels. Autonomous vehicles will likely prove to reduce fuel consumption, improve traffic conditions, and be environmentally friendly.
Humans are highly mobile traveling at many scales. We use airplanes to travel across the country and around the world but we also travel in large volumes at a much more local level. Many people commute daily across a city or travel small distances on a regular basis. The modes of intermediate distance travel include walking, biking, driving, and using public buses and subways. There will always be a need for a cars because there are enough people that need to travel intermediate distances in diffuse numbers and irregular patterns that cannot be accommodated through mass transportation.
Prototype self-driving cars have existed in one form or another for several decades. There are currently no commercially available autonomous vehicles but several companies have developed fully operational autonomous vehicles (see Fig. 1).  Self-driving cars road pose a multitude of legal, moral, and economic questions. [5,6] For example, if a self-driving car hits a pedestrian who is at fault? It is possible that the car manufacturer will be liable for the way the driving algorithm was implemented. The issue gets even more complex if the car can be operated manually by a driver and the driver strikes the pedestrian. Many of these issues will be worked out with the implementation of putting self-driving cars on the road.
An efficient method that we propose in this paper that is able to bypass legal/moral questions is as follows: a specific population could have a fleet of autonomous vehicles.  These cars could act essentially as a taxi service alleviating the need for many people to own cars and even eliminate the need for drivers. A traveler could summon an autonomous vehicle, enter the car, and get to his/her destination without even having to drive.
Self-driving cars have many advantages over a human driver making them much safer.  A human sitting in a car is only able to view from his/her vantage point and have relatively slow reaction times. Furthermore, humans can become distracted or drowsy making driving dangerous. Self-driving cars are constantly alert and can view the road from multiple vantage points. They are also more reliable and have quicker reaction times than human drivers. One major cause of traffic jams is car accidents and self-driving cars will cause fewer accidents than humans. 
The average amount of fuel, F, consumed by a car can be expressed as F=d/mpg, where d is average travel distance, and mpg is miles per gallon. Autonomous vehicles can be used to change each of these factors to reduce the overall fuel consumption F.
|Fig. 2: Self-driving cars can lower the number of accidents and speed up traffic. (Source: Wikimedia Commons)|
Human drivers are responsible for much of the traffic congestion. Many traffic jams (such as the one in Fig. 2) are a result of accidental crashes. Traffic also tends to slow down when drivers are not paying attention and sitting still for too long in stop-and-go traffic. With safer conditions, self-driving cars will have fewer accidents thus keeping the roads clearer. Self-driving cars can also reduce the distance between vehicles and be fully alert and travel on roads more efficiently than human drivers. Will less stagnant traffic there will be fewer cars idling on the roadway thus reducing the time that cars spend on the road thus increasing mpg (and reducing overall fuel consumption, F).
Another proposed idea to reduce traffic is "Road Trains" which consist of a line of cars capable of communicating with each other and which drive down a highway. The space between these cars can be reduced to lengths smaller than humans can safely manage as the reaction time over such a small distance is too small for a human driver. Road Trains will condense traffic and can even be optimized for fuel efficiency by reducing wind drag (increasing mpg and lowering F). 
Furthermore, self-driving cars can plan optimal travel routes (to decrease d).
When self-driving cars are used as proposed it will be easy to refuel each vehicle with renewable energy fuel. For example, electric cars can be charged with electricity that is produced at a generator. Electric vehicles are less expensive and cleaner to operate than gas powered vehicles.  This would make it easier for all the cars to operate with clean and cheap energy.
Gasoline prices are very volatile and related to political climate as well as demand and supply.  Currently electric vehicles are able to travel much further per dollar than gas-powered vehicles.  As oil production decreases electric vehicles will continue to become more economical.
Furthermore, it has been shown that an optimal travel speed can be chosen to maximize miles-per-gallon.  Self-driving cars can be programmed to drive in a way that is fuel efficient. By programming travel speeds, accelerations, and even mapping out optimal travel routes self-driving cars can be programmed to reduce power consumption.
As self-driving cars become more ubiquitous and available for transportation to the public we need to take into consideration what is more important. Do we prefer to get places fast or do we want to save fuel? Each of these things can be automated into a self-driving car.
Self-driving cars are advantageous to manual cars in many ways. They can minimize the need for people to own and drive cars. Furthermore, with potentially fewer cars on the road, we can reduce traffic congestion, minimize travel time and/or optimize for fuel efficiency. Self-driving cars still have many challenges to overcome before they are widely used in the United States and worldwide. Self-driving electric cars are advantageous over the status quo.
© Dustin Gerrard. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "BP Statistical Review of World Energy," British Petroleum, June 2014.
 Y. Zhang et al., "Remaining Driving Range Estimation of Electric Vehicle," IEEE 6183172, 4 Mar 12.
 "Key World Energy Statistics 2014", International Energy Association, 2014.
 S. Pacala and R. Socolow. "Stabilization Wedges: Solving the Climate Problem For the Next 50 Years With Current Technologies," Science 305, 968 (2004).
 C. Urmson and W. Whittaker, "Self-Driving Cars and the Urban Challenge," IEEE Intel. Syst. 23, 66 (2008).
 N. J. Goodall, "Ethical Decision Making During Automated Vehicle Crashes," J. Trans. Res. Board., U.S. National Research Council 2424, 58 (2014).
 L. D. Burns, "Sustainable Mobility: A Vision of Our Transport Future," Nature 497, 181 (2013).
 E. Coelingh and S. Solyom. "All Aboard the Robotic Road Train," IEEE Spectrum 49, No. 11, 34 (2012).
 O. Van Vliet et al., "Energy Use, Cost and CO2 Emissions of Electric Cars," J. Power Sources 196, 2298 (2011).
 C. Dahl and T. Sterner, "Analysing Gasoline Demand Elasticities: A Survey," Energ. Econ. 13, 203 (1991).
 J. Rouwendal "An Economic Analysis of Fuel Use Per Kilometre by Private Cars," J. Transp. Econ. Policy 30, 3 (1996).