It can take 12 years or more to get a green light for new multifamily buildings on Long Island, and the delays are driving up rental prices and causing a shortage of new construction, a new report finds.

In order to bring rental prices down and provide more housing for young adults and retirees, Long Island should make it easier to build in downtowns, the Garden City-based Long Island Index recommended in a report due to be released Thursday.

Major new construction projects on Long Island often face numerous regulatory hurdles as well as fierce opposition from neighbors who fear the new buildings will harm the environment, increase traffic and decrease property values.

In the new report, titled “The Long Campaign: What It Takes to Build Apartments on Long Island,” the Long Island Index concludes that the resulting delays have created a shortage of rental and condominium construction that results in higher costs.

Long Island one-bedroom apartments fetched a median price of $1,709 in Nassau County and $1,470 in Suffolk County last year, compared with $1,180 in northern New Jersey and $1,376 in Westchester, according to the report.

Rentals make up about 20 percent of the housing stock on Long Island, compared with 37 percent in northern New Jersey and 34 percent in Westchester, the Long Island Index reported.

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“We are the makers of our own misery,” said Ann Golob, director of the Long Island Index. “Why are rents so high? Because we make it so hard to build here.”

New downtown construction can benefit local communities such as Patchogue and Mineola without damaging the environment or causing other harm, she said. “No one wants to see development at the expense of the environment,” Golob said, “but there certainly are ways to balance both.”

The paper, written by Elizabeth Moore, a former reporter for Newsday, examines how long it has taken one developer — AvalonBay Communities, a Virginia-based real estate investment trust — to get approvals for construction on Long Island compared with other areas.

AvalonBay has spent between two and eight years seeking the go-ahead to build on Long Island; in some cases, individual projects have taken 12 years or longer, factoring in the time spent by a previous builder whose efforts failed, the report found.

By contrast, it took AvalonBay just four months to get approval to construct a 20-story building in upper Manhattan, according to the report.

In Huntington Station, AvalonBay’s proposal for 490 new apartments near the train station was rejected by the Huntington Town Board in 2010. Years of community opposition and more than a year of litigation ensued. It took until 2014 to open a scaled down, 379-unit complex, which includes 43 affordable units.

The apartments are about 98 percent occupied, the developers said.

“I’ve certainly had folks come up to me who were at least on the fence, if not opposed, and say, ‘Hey, you know what, the community looks great,’ ” said Christopher Capece, a senior development director with AvalonBay. “A lot of the fear and concern has been addressed and to a large extent has gone away.”

But one Huntington resident who opposed the project, Steven Spucces, said he still believes it is too dense, adding too many cars to local streets and harming the environment. Communities should place more barriers — not fewer — in the way of large-scale development, he said.

“The zoning laws were put there for a reason,” Spucces said. Major developments, he said, harm the Island’s environment, strain its infrastructure, add too much traffic, “and at the end of the day, the taxpayers are going to be the ones to foot the bill.”