A Mount Prospect, Illinois school bus driver who smelled of alcohol to a co-worker managed to drop off 50 children before she was arrested Tuesday for being nearly three times over the legal limit for alcohol, police said.

A transportation supervisor in Mount Prospect School District 57 tracked down the driver and called police, but allowed her to continue on her route until authorities arrived, school officials said Wednesday.

Lisa Black and Carlos Sadovi of the Chicago Tribune report that Betty Burden, 54, was arrested after police received a call around 3:45 p.m. Tuesday from the supervisor, Vincente Ramirez.

School board President Joseph Leane said another driver had smelled alcohol on Burden’s breath around 2:30 p.m. but did not report it to Ramirez until 3:30 p.m.

Officials said Ramirez immediately set out and caught up with Burden along her route from Lions Park Elementary School, where she was scheduled to pick up students being released at 3:35 p.m. Ramirez boarded the bus, but because he could not verify that she had been drinking, he followed Burden along her route and called police within 15 minutes, officials said.

"There were children on the bus during the time she was under the influence," Superintendent Elaine Aumiller said. "Thank God nothing happened."

Aumiller said that because of legal restrictions, Ramirez did not confront Burden or ask if she had been drinking. Because he could not smell alcohol or detect physical signs that she was intoxicated, he instead called police and followed her along her bus route, Aumiller said.

Aumiller stood behind Ramirez, calling it a "tough administrative call." She said Ramirez might have waited to call police until the children were off the bus "so they don’t become witness to an arrest."

"It’s such a delicate decision, to make an accusation of this nature against somebody," she said. "You have to have compelling evidence that it is there, and it wasn’t there for him."

During Burden’s appearance in bond court Wednesday, Assistant Cook County State’s Attorney Mark Javier said Ramirez observed Burden driving erratically, though school officials denied that. Ramirez could not be reached for comment.

On Wednesday, Burden was charged with felony aggravated driving under the influence of alcohol because she was transporting passengers under age 18 at the time, officials said. She has been suspended from the school district without pay. School officials will recommend that Burden be fired during the next school board meeting, Aumiller said.

Police said they "immediately smelled the odor of an alcoholic beverage on Burden’s breath," noticed other physical signs of alcohol impairment, then administered field sobriety tests, which she failed. Burden consented to a breath test, which registered her blood-alcohol level at 0.226, officials said. The legal limit is 0.08.

Burden admitted drinking vodka and orange juice before driving, prosecutors said. She drove for the district from 1991 to 1999, then again starting in August 2008.

Leane, the school board president, said Ramirez was following federal transportation regulations that indicate that a supervisor must have "actual knowledge" that a driver has been drinking to stop that person from driving.

Many parents angrily questioned why Burden had been allowed to drive her route but declined to comment on the record.

Parent Dawn Byrne, who learned of the incident Wednesday through an automated message, said she was surprised to hear that regulations would keep an administrator from stopping a suspected drunken driver.

"I wouldn’t appreciate that as a parent only because if someone’s questioning it, you would think they have to take full responsibility at that time to make sure our children are safe," said Byrne, who has two children in the district. "It’s all about the kids’ safety, not how he’s following procedure."