Making a left turn on a 2-way street in the United States can take a while. Those few extra seconds add up for a company like UPS, which operates 96,000 trucks. Since 2001, the company has closely examined how it can become more efficient. It found that left turns waste a lot of time sitting at stop lights. It would save gas to just make right turns.
So, in 2004, the company created a navigational program that would map driving routes with just right turns. It’s not only thrifty, but environmentally fiendly. Alex Mayyasi writes for Priceconomics:
As of 2012, the right turn rule combined with other improvements -- for the wow factor, UPS doesn't separate them out -- saved around 10 million gallons of gas and reduced emissions by the equivalent of taking 5,300 cars of the road for a year.
Mythbusters agrees. The television program tested UPS’s method and found that it worked.
-via VA Viper