In the 1970s, disco-themed skating rinks were all the rage. In the '80s it was paintball battlefields, followed in the '90s by urban skateboard parks.
And now comes the zip line — an elevated cable ride that zips harnessed riders downhill at high speeds, powered only by gravity.
Across the nation, these rides stretch over canyons, vineyards, island tourist towns and even zoos. Since 2001, the number of zip lines built in the U.S. has soared from 10 to more than 200, according to zip line experts.
Today, zip lines rise above parts of Catalina Island, run through the forest near Big Bear and tower over San Diego Zoo Safari Park, where riders get a bird's-eye-view of giraffes, rhinos and antelopes. A 720-foot-long ride has been proposed to race over parts of Venice Beach this summer.
"They are spreading like fast-food hamburger joints," said Mike Teske, technical director for a Maui–based zip line company, who also heads a panel drafting national safety standards for zip lines.
The craze is fueled by a resurgence in the popularity of outdoor activities, greater availability of insurance, and cheaper construction costs for zip line platforms due to the housing slump, according to builders and operators. The prices to ride vary widely: It costs $10 to ride an 800-foot zip line at a KOA camp in Santa Paula, for instance, but $112 to ride two zip lines at the San Diego Zoo Safari Park.
In addition, builders and operators point out, zip lines have wide appeal to both young and old. The only physical demand is the climb up the steps of the platforms, where guests wearing harnesses are hooked to a pulley that allows them to travel along the zip lines' steel cable, with typical speeds reaching 35 to 45 mph and faster. The most advanced zip lines have built-in brakes. On the basic models, riders must slow themselves with a gloved hand.
Like roller skating and paintball battles, the promise of an adrenaline rush draws many first-time riders.
"I tried it because going to the movies and going bowling is getting boring," Tyler Montague, 21, a graphic design intern from Huntington Beach, said after a three-hour tour at Action Zipline Tours in the mountains near Big Bear Lake.
Other riders say they try a zip line once — just to check it off their before-you-die bucket list.
"I'm 64 years old, and I don't think I'll do it again," John Rockwood, a retiree from Buffalo, N.Y., said after joining his wife, Julia, on the Big Bear zip line.
Not everyone is thrilled by zip lines — especially in areas where critics say proposed routes can spoil scenic views or disturb wildlife. Near Big Sur, for instance, activists are fighting a proposed zip line in Jacks Peak County Park.
Some Venice Beach residents expressed concern about safety and noise from screaming patrons. The plan for a zip line has been approved for a three-month trial by the Venice Community Council, but it has yet to be scheduled for a hearing by the California Coastal Commission. Supporters hope the zip line — stretching from a 44-foot tower near the skate park to a 24-foot tower at Windward Plaza by the basketball courts — could open by July 1.
Zip lines have become such a boom industry, particularly in California, that a private group is setting new voluntary safety standards for these rides.
The guidelines are being written by Pennsylvania-based ASTM Inc., formerly known as the American Society for Testing and Materials. The group has previously drafted safety rules for helmets, medical devices and steel products. The work began two years ago, and officials estimate that the voluntary rules could be drafted in the next year or two.
In the meantime zip line operators said they are relying primarily on safety standards written by the Association for Challenge Course Technology, an Illinois group that began writing guidelines in 1994 primarily for zip lines and rope courses used by churches, Boy Scouts and schools, among other private groups.
"Everyone agrees that new standards are a good thing," Teske said.
No government agency keeps records of zip line injury rates, but zip line operators and insurance providers say injuries are typically severe but very rare. A worker was killed and another man injured last year while making modifications to a zip line in Hawaii, home to more than a dozen zip lines. In 2010, actor Hugh Jackman injured his eye when he rode a zip line for an Oprah Winfrey television special in Australia and ran into lighting gear.
But most zip line injuries, say zip line operators, take place on lines built by amateurs who ignored safety requirements.
Since the craze took off a few years ago, the number of insurance firms in the country willing to write policies for commercial zip line operations has grown from about two to 10, said Robert P. Monaghan, executive vice president at Hibbs-Hallmark & Co., a Texas insurance firm that has written zip line policies for several years.
"Insurance is reasonable if they build it properly, train their staff properly and subject themselves to third-party inspections," he said.
Construction costs for zip lines vary by the model and length of the ride and the terrain. The nine zip lines at Action Zipline Tours in Big Bear cost about $2 million to build while the two zip lines for San Diego Zoo Safari Park cost $3 million, operators said.
Zip line experts trace the birth of the trend to Costa Rica and other South American countries, where canopy tours of the rain forests used zip lines to whiz tourists from one tree to another. American tourists who rode the South American zip lines brought the craze to the U.S., where the lines first appeared at summer camps for children.
Thaddeus Shrader can attest to the popularity of zip lines. He's the chief executive of Colorado-based Bonsai Design Inc, one of the nation's largest builders of zip lines and rope courses.
His company has grown from six full-time workers in 2008 to 73 today, with offices in North Carolina and West Virginia. He estimated that his company will gross $7 million in sales this year, compared with $5 million last year.
"As North Americans have seen how much fun they are," he said, "zip lines have just taken off."