New study details the mileage you lose by driving too fast
Motorists want to have their cake and eat it too, says a new study conducted at the Oak Ridge National Laboratory, in Knoxville, Tenn. Not only do drivers want more fuel-efficient vehicles, they also want higher speed limits. Not surprisingly, fuel efficiency drops exponentially by increasing your speeds as little as 10 mph. What’s interesting is that decreased fuel economy may not vary as much amongst different vehicles, according to the new study.
In fact, the research points out that there are relatively few differences between a massive SUV and a sleek aerodynamic sports car.
“People really like rules of thumb, and if you’re increasing your speed from 50 to 60 miles an hour, we find for the largest number of vehicles fuel economy will go down about 12 percent,” said Brian H. West, a researcher at the Oak Ridge National Laboratory.
Although 12 percent is a significant drop, that’s just the beginning, says West. Simply driving 10 mph faster (60 to 70 mph) will cause fuel economy to decrease 14 percent, while driving 80 mph can cause a 16 percent dip. Simply put, a vehicle that gets roughly 40 mpg at 50 mph would only get about 25 mpg at 80 mph.
The correlation between excessive speeds and decreased fuel economy is not anything new, but researchers did stumble upon a surprising discovery. Researchers had assumed that different vehicles would fare better than others, but ultimately found that there is little variation. In fact, fuel economy is consistent across all vehicle segments. Interestingly, the study found just a one to two percent deviation between the heaviest vehicle and the most fuel-efficient model.
The study also concluded that even hybrid vehicles fell subject to declining fuel economy. Although hybrids are engineered for stop-and-go city driving, highway driving proves detrimental when it comes to fuel efficiency. Specifically, hybrids cannot regenerate enough energy to counteract the gasoline they use when traveling at highway speeds. This is primarily the reason why hybrids have lower EPA estimated highway mileage ratings compared to city.
Only time will tell if studies like the one conducted by West deter calls for increased highway speeds. Highway speed limits have substantially increased since Congress lifted federal restriction in the 1970s. Most recently, Texas opened the nation’s fastest highway, which boasts a top speed of 85 mph.
In the meantime, automakers will be forced to meet increasing fuel economy requirements, while also battling the lead foot of the consumer. In August, the Obama Administration finalized a groundbreaking new standard that increase fuel economy to 54.5 mpg for cars and light-duty trucks by model-year 2025.