Around 9:30 p.m. on St. Patrick's Day, Sarah Melissa Steed's car became disabled on Wadmalaw Island.

Her Toyota ended up parked perpendicular to oncoming traffic on Maybank Highway, its passenger side facing the cars traveling in her lane. When a vehicle struck her car, she was on the far side, deputies said, changing a tire.

Steed's own car then hit and critically injured the Hartsville woman.

Investigators don't know why the 29-year-old's car had stopped where it did. But because it was parked in the right of way, they haven't charged the man whose vehicle hit hers with a more serious crime than drunken driving.

Dennis Patrick O'Keefe, 59, of Anchor Watch Drive on Wadmalaw faces a misdemeanor charge of first-offense driving under the influence with less than a 0.10 percent blood-alcohol content.

Under state law, a drunken driver who causes great bodily injury to someone could be charged with felony DUI, which carries between 30 days and 15 years behind bars. The statute states that the driver must be intoxicated and that his illegal act or neglect caused the victim's injury.

In Steed's case, deputies with the Charleston County Sheriff's Office found her partially at fault for the crash because her car was in the road.

But sheriff's Maj. Eric Watson said the investigators were discussing with the 9th Circuit Solicitor's Office whether the felony charge might still be levied.

"She was blocking the road," Watson said. "That's one of the areas we're reviewing ... to make sure the charges are appropriate."

Watson said that deputies were able to speak with Steed but that they didn't learn why her 1999 Toyota was positioned pointing toward the shoulder of the southbound lane of Maybank Highway near Bears Bluff Road.

They indicated in a collision report that O'Keefe's 2008 Nissan was on a slight curve when it veered toward the northbound lane in an attempt to avoid Steed's car. But the Nissan struck the back passenger side.

The impact threw Steed to the shoulder of the two-lane highway.

The speed limit in the area is 55 mph, and deputies said O'Keefe was going about 60.

To Mount Pleasant attorney Charlie Condon, a former state attorney general, speeding or a drunken driver simply getting behind the wheel could be the illegal acts that investigators must prove for the felony DUI charge.

But he said investigators also must examine whether a crash was unavoidable even for a sober driver.

"But cars often are stalled on highways," he said. "If someone is drunk and rams into them and kills someone, I would expect an arrest for felony DUI."

It was O'Keefe's first arrest in South Carolina, according to the State Law Enforcement Division. Watson said deputies had not completed an incident report that detailed the arrest. He posted $997 bail and left the jail 10 hours after he arrived.

Steed was taken to Medical University Hospital. Her condition Friday was not immediately known.

Reach Andrew Knapp at 937-5414 or twitter.com/offlede.