One man tossed his bike over a fence and pedaled across a runway at Chicago O’Hare, stopping to knock on a terminal door. Another rammed a sports-utility vehicle through a security gate at Philadelphia International and sped down a runway as a plane was about to land.

At Los Angeles International, a mentally ill man hopped the fence eight times in less than a year — twice reaching stairs that led to jets.

Several hundred times over the last decade, intruders have hopped fences, slipped past guardhouses, crashed their cars through gates or otherwise breached perimeter security at the nation’s busiest airports — sometimes even managing to climb aboard jets.

An Associated Press investigation found 268 perimeter breaches since the start of 2004 at airports that together handle three-quarters of U.S. commercial passenger traffic. And that’s an undercount, because two airports among the 31 that AP surveyed didn’t have data for all years. None of the incidents involved a terrorist plot, according to airport officials.

“Enough is enough,” U.S. Sen. Barbara Boxer, D-Calif., said in response to the AP report, adding that since a breach last April in San Jose she’s been asking the Transportation Security Administration and airport officials to “work together and resolve this alarming situation.”

“Let’s get it done,” she said.

The TSA referred questions to individual airports, which are responsible for securing their own perimeters, typically with a mix of private security guards and airport police.

“The goal is always zero” breaches, Doug Yakel, spokesman at San Francisco International Airport, said at a news conference called in response to the AP’s findings. He outlined security upgrades the airport has made that include more patrols, better lighting and the installation of cameras that can detect body heat at night.

San Francisco’s airport had the most incidents in AP’s analysis, with 37. Philadelphia International and LAX followed, with 25 and 24 respectively.

In his regular his “Ask the Mayor” segment on KNX-AM radio, Los Angeles Mayor Eric Garcetti called the findings “disturbing.”

“It doesn’t surprise me that we’re in the top three given that we’re the second-busiest airport in the United States, but that’s disturbing to see,” he said. “All it takes is one person who can get through and do something.”

His office said LAX within the next year will begin testing an electronic perimeter intrusion detection system at a cost of $1.5 million.

The AP’s analysis was prompted by last April’s breach at Mineta San Jose International Airport. Yahya Abdi, 15, climbed a fence, hoisted himself into a jet’s wheel well and survived an almost six-hour flight to Hawaii. He had wanted to go to Africa to see his mother.

Afterward, an airport spokeswoman said breaches are more common than people realize.

Through public records requests, news archive searches and interviews, the AP created the most comprehensive public accounting of perimeter security breaches from January 2004 through January 2015 at the nation’s 30 busiest airports, plus San Jose.

Among the findings:

— At least 44 times, intruders made it to runways, taxiways or to the gate area where planes park to refuel or load passengers. In seven cases, including Abdi’s, they got onto jets.

— Seven international airports in four states accounted for more than half the breaches, although not all provided data for all years examined. In order they were: San Francisco, Philadelphia, Los Angeles, Las Vegas, San Jose, Miami and Tampa, Florida. The Port Authority of New York & New Jersey, which oversees Kennedy, LaGuardia and Newark airports, did not provide a full accounting of perimeter breaches. Boston’s Logan refused to release any information, citing security concerns.

— Few airports revealed how long it took to apprehend suspects, saying this detail could show security vulnerabilities. Available information showed most arrests happened within 10 minutes. Several people went undetected for hours or never were caught.