Baltimore Police Officer Teresa Rigby was handling the most routine call on one of the city's most treacherous roads.

Just three years out of the academy, the officer was watching a tow truck driver hook up a disabled car on the northbound Jones Falls Expressway — an elevated, curving highway with narrow breakdown lanes and lined with Jersey barriers marred with scrapes from cars whose drivers veered out of their lanes.

It's a stretch of road where, a former police official says, officers hesitate to pull over speeders because it's too dangerous to stop.

At 9:20 a.m., a black Saab struck the back of Rigby's cruiser just south of Cold Spring Lane, hitting or forcing her off the highway and onto the parking lot of a Pepsi plant some 30 feet below.

"All you seen was her going over," said Butch Dews, 63, who was working at a nearby construction site and looked up when he heard a car braking and tires screeching.

The 27-year-old officer was rushed to Maryland Shock Trauma Center, where she was listed in critical condition with injuries that included multiple leg fractures.

Dr. Thomas Scalea, physician-in-chief of the trauma center, told reporters before 1 p.m. that Rigby was on life support and would be going into surgery. Rigby had "arrived arousable but not awake," Scalea said.

She was "still in a very dynamic stage of care," and doctors needed to stabilize her before surgery, the doctor said. Hours later, the city police union president, Robert F. Cherry, visited the hospital and said that Rigby was "going to be fine."

Mayor Stephanie Rawlings-Blake said she spoke with the officer's family and said they were "remarkably calm." Relatives and fellow police officers visited her at the hospital. "Everybody's praying for a speedy recovery," the mayor said.

The crash that closed the busy highway for four hours was a reminder that the greatest danger for police officers is cars, even in a city fraught with gun crime.

For the past decade, auto-related accidents were the leading cause of death for police, said Chris Cosgriff, executive director of the Officer Down Memorial Page Inc., a nonprofit that honors fallen officers nationwide. Baltimore Police lost two officers to traffic-related fatalities last fall.

Cherry said he has asked the Police Department's new chief of patrol, Col. Dean Palmere, to require multiple officers to respond to traffic stops or accident scenes on the highway. "It's another example of how dangerous I-83 is," he said. "We've got to make sure that there's multiple cars to assist. Teresa was on her own."

Legislators have been tweaking laws in response to officer safety concerns. Several jurisdictions banned policies that had officers step into roads to flag down speeding motorists, and in October, a state law took effect requiring drivers to move over one lane or to slow down when passing emergency vehicles on the side of the road with flashing lights.

"The intent of the 'move over' law is to provide that barrier of safety for any emergency responders," said Maryland State Police spokeswoman Elena Russo.

"Anybody who's distracted behind the wheel, on their cellphone or just not paying attention, they all put our emergency responders, our police officers, put them all in harm's way," she said.

Despite several pushes to get the word out, officials say few motorists are aware of the law. Violators face a $110 fine and one point on their licenses. If the violation causes a crash, the penalty increases to $150 and three points. The fine for fatal crashes, or those that cause serious injury, is $750 and three points, Russo said.

Cosgriff said he frequently sees people violating move-over laws. "There's a lot of room for enforcement here," he said. "Not only is it the law, but to me it's common sense."

Maryland State Police troopers take officer survival skills and traffic safety courses at the academy, Russo said.

Troopers are taught alternative approaches to traffic stops and are urged to approach on the passenger side, she said. "It's a safer approach than hugging the edge line," she said.