A woman died on a San Francisco stretch of freeway Monday, in a crash investigators say involved no vehicles besides her own.

It was 12:06 p.m. Monday when a woman piloting a Harley-Davidson motorcycle crashed on northbound Highway 101 near the Ninth Street off-ramp, California Highway Patrol spokesperson Officer Vu Williams says.

The woman "apparently failed to negotiate a curve in the roadway and struck a barrier," Bay City News reports. She died at the scene, Williams says. The San Francisco Medical Examiner's Office has since identified the motorcyclist as 51-year-old SF resident Macshell McIlvenna.

The wreck and subsequent investigation blocked lanes of 101 until just after 2 p.m., causing a significant traffic backup in the area.

A caller who reported the crash said that the motorcyclist had been in a collision with a black Honda Accord, the Chron reports. However, investigators "later determined the [Honda driver] merely witnessed the crash and was not involved," BCN reports.

“It looks like it was a solo collision,” Williams told the Chron “Early indications are, it may have just taken that curve a little too fast — speed is probably going to be a factor here.”