The spectator behind one of the biggest pile-ups in Tour de France history appeared in court charged with injuring dozens of riders but seemed set to avoid jail after prosecutors demanded a suspended sentence.

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" for causing what some dubbed the "worst crash ever seen" in the famous race.

Wearing a blue sweater, she fled the scrum of journalists waiting at the courthouse in Brest, in western France.

But the presiding judge rejected a request by her lawyer to have the trial held behind closed doors.

While jail time was a real possibility, the prosecution requested that she be given a four-month suspended sentence on the charges of endangering lives and causing unintentional injuries.

Bryan Coquard of France after the crash. Photo / Getty

Under French law she could have faced a fine of up to 15,000 euros ($AUD23,00) and a year in prison for the charges.

Prosecutor Solenn Briand acknowledged that she had recognised "how dangerous" her conduct had been and had expressed regret.

The trial was adjourned for a verdict on December 9.

The woman, who has no criminal record, had attended the opening Tour stage on June 26 with the goal of getting a sign noticed by TV cameras. It read "Allez, Opi-Omi", 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 organisers, especially when they realised 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.

But the woman's lawyer Julien Bradmetz said his client had had "a fragile personality for many years".

"This fragility has now increased tenfold so today my client is living through hell," he said.

The trial opened the same day as organisers unveiled the route and stages for next year's race, which will start in Copenhagen and also includes routes in Switzerland and Belgium.

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

Christian Prudhomme, director of the Tour, adopted a conciliatory stance over the case as he announced the new route in Paris.

"She did something daft, she's no terrorist. We just want people to take care when they come to the Tour and remember they are there to see the champions and not to get on television," he told reporters.

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 behaviour 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."