Parking revenue in the U.S. is projected to grow by $4 billion over the next two years, according to a report released Wednesday.
The National Parking Association (NPA) estimates that revenue from parking will increase from $25 billion last year to nearly $29 billion by 2018.
But some experts worry that autonomous vehicles could eventually make parking obsolete and hurt local governments, when drivers are able to put their cars in self-driving mode instead of finding a parking spot.
Currently, private parking owners and public parking operators together employ more than 143,000 people, according to the NPA, and approximately 120 million Americans drive to work everyday.
The two states bringing in the most parking revenue are California and New York, with $1.4 and $1.2 billion, respectively. The report says New York, Los Angeles, Chicago, Houston and Phoenix have the most parking growth potential.
The primary driver of the rising parking demand is population expansion, which is estimated to increase from 320 million in 2015 to 400 million by 2050.
Other economic and demographic factors underpinning parking growth include higher employment, more commuters, more people driving for vacations and municipalities increasing parking development.
"The purpose of this study is to understand the long-term parking demand potential and the trends that are shaping the future of the parking industry," Christine Banning, president of the NPA, said in a statement Wednesday.
Some of the factors that could decrease parking include unemployment, rising fuel costs, decreasing growth domestic product and zoning laws that limit parking lot construction, the NPA noted.
The report doesn’t identify self-driving cars as one of the factors that may drive down parking revenue. However, although companies like Ford are planning to build a fully driverless car by 2021, such vehicles are not likely to be available to the masses for decades.