The spectator behind one of the biggest pileups in Tour de France history goes on trial Thursday charged with injuring dozens of riders on the cycling race's first day in June.

The 31-year-old French woman, whose identity was withheld after she was targeted by a torrent of online abuse, has already told prosecutors of being ashamed at her "stupidity."

She was hoping to get a sign noticed by TV cameras saying "Allez, Opi-Omi," using the German terms for "grandpa and granny," a nod to her family's German roots.

But she stepped out too far in front of the tightly packed peloton as it sped along a narrow road toward the finish at Landerneau in western France.

German rider Tony Martin was unable to avoid bumping into her and fell, forcing dozens of riders to crash while others swerved into the crowds of onlookers.

Video footage of the collision and ghastly scenes of medics tending stunned or grimacing victims sparked outrage among fans and race organizers, especially when they realized the woman had fled the scene instead of ­staying to help.

She remained in hiding for four days before turning herself in to police. Several riders had to pull out of the race, including Spain's Marc Soler, who had both arms broken.

Charged with endangering lives and causing unintentional injuries, she risks a fine of up to 15,000 euros ($17,300) and a year in prison. It seems unlikely that she will spend time behind bars, however, as the public prosecutor of Brest noted after her arrest on June 30 that she had some "personal vulnerabilities."

The Tour's organizers, the Amaury Sport Organization (ASO), had originally planned to sue but later said it wanted to "calm things down" and would not be a plaintiff.

But the Switzerland-based International Association of Riders (CPA) has maintained its complaint and is seeking a symbolic one euro in damages to send a message against dangerous fan behavior during stages.

"The damage suffered by the riders is physical, moral and economic," CPA president Gianni Bugno said in a statement Wednesday.

"An athlete prepares months for a grand tour and it is not acceptable that all his hard work, that of his family, his staff and his team, should be shattered in an instant by the quest for popularity."

A source close to the case said the lawyer could argue that race organizers had failed to take sufficient security measures, citing the series of accidents that marked the 108th edition of the Tour.