So far in 2015, U.S. auto sales are running at a pace of 17.2 million vehicles. If sales continue at this rate, 2015 will be the second-best year ever for auto sales, trailing only 2000 when the industry hit a high-water mark of 17.4 million vehicles.
"It's going to be challenging for automakers to push sales much higher," said Mark Wakefield with AlixPartners.
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The problem? The U.S. has become increasingly saturated with new vehicles following an extended up cycle where sales will have jumped 67 percent.
After hitting a high next year, auto sales are expected to pull back steadily in a three-year down cycle that will bottom out with annual sales of 14.9 million vehicles in 2019, according to the study.
"That would be a moderate downturn," Wakefield said. "One thing we are baking in is automakers not slashing prices and artificially boosting demand with excessive incentives."