A study on crash factors in intersection-related accidents from the US National Highway Traffic Safety Association shows that turning left is the cause in 22.2 percent of crashes, as opposed to 1.2 percent for right turns. About 61 percent of crashes that occur while turning or crossing an intersection involve left turns, as opposed to just 3.1 percent involving right turns.
Left turns are also three times more likely to kill pedestrians than right ones, the New York Times reported, according to data collected by New York City's transportation planners.
"A left-hand turn is also less fuel efficient," Jack Levis, UPS Senior Director of Process Management told CNN, "because your car's idling longer, which is also not good for your vehicle."
UPS does not ban left turns outright, says Levis: "We will make left-hand turns, but not ones that are unnecessary. We don't need to go in circles all day long by making only right-hand turns. We have tools analyze the number of left-hand turns for each route, and we can work out which ones are avoidable."