A crash in December grabbed headlines – a school bus swerving out of control and flipping on a winding road, the driver arrested on charges she was under the influence of multiple prescription drugs.

But while it was unusual to have an allegedly intoxicated school bus driver in an injury accident, the fact that a Colorado school bus had been in a wreck was not – since 2011, they’ve been involved in more than 1,500 crashes in the state.

That’s an average of two bus crashes a day – every day – during the school year.

“That’s absolutely surprising,” said Rebecca Matheson, whose son was injured in a 2011 crash in Adams County. “It’s scary. It’s very scary.”

And that doesn’t include numbers for the last half of 2015, which aren’t expected to be available until late April.

The 9Wants To Know investigation, conducted with Rocky Mountain PBS News, began with a detailed examination of accident data compiled by the Colorado Department of Transportation. The data included school bus crashes between Jan. 1, 2011, and June 30, 2015 – covering four full school years and half of a fifth.

That data provided an unprecedented look at school bus crashes in Colorado:

More than 700 of the crashes were deemed by police investigators to be the fault of the bus drivers.

More than 70 of those crashes caused by the bus drivers resulted in injuries – 377 people in all were hurt, including children on buses and motorists and passengers in vehicles they smashed into.

Two of the accidents resulted in the deaths of pedestrians – both older people who were hit by buses, one in Loveland, one in Westminster.

All but one of Colorado’s 178 school districts provide bus transportation to students in some form. According to Jennifer Okes, director of school finance at the Colorado Department of Education, more than 363,000 students ride buses on the average day.

“It is a very safe mode of transportation, but clearly we need to continue to do everything we can to review the procedures and policies and rules so that it gets even safer,” Okes said.

Two frightening crashes that occurred in late 2015 illustrated that crashes can happen any time – and that the consequences can be serious.

The first was Nov. 17 outside Durango. A driver who was a week out of training was reaching for a whistle to quiet noisy students when he lost control. The bus drifted off the road, ran down an embankment and rolled over, injuring 10 students. The driver, William Farley, was also injured and was cited with careless driving causing bodily injury.

Then came the Dec. 7 crash outside Lyons involving a driver, Elizabeth Burris, who faces multiple charges amid allegations that she was under the influence of as many as six prescription drugs and unable to pass a roadside sobriety test. Five of the eight students on her bus were hurt, and Burris suffered minor injuries.

She now faces multiple charges – driving while under the influence, two counts of vehicular assault and eight counts of child abuse.

Corbyn Fillweber, 12, and his brother, Tyler Fillweber, 10, were on the bus that day.

After those two crashes, 9Wants To Know set out to find out just how often school buses get into wrecks in Colorado. The investigation was focused on the more than 700 crashes in which the school bus drivers were deemed by investigators to be at fault.

The data provided a detailed look at those incidents.

At least one in five of the wrecks was a result of a serious factor affecting the driver. For instance, in 69 cases a driver who crashed was preoccupied or distracted by passengers, and in 47 accidents a driver’s inexperience played a major role, according to the data.

At the same time, weather conditions – while playing a role in a number of crashes – accounted for only about a quarter of the wrecks.

Buses hitting parked cars accounted for the largest number of the wrecks – but the data also showed that rear-end crashes were the source of the most injuries.

That’s exactly what happened in the accident when Matheson’s son, Will, was injured on Oct. 5, 2011. He was 14 at the time and riding on a bus driven by Sheryl Ritchey, a driver for Adams County School District 12 since the mid-1990s.

Ritchey declined a request from 9NEWS for an interview.

According to the Westminster Police Department report on the crash, her bus was traveling 46 mph in a 40 mph zone when she slammed into the back of a Mitsubishi Eclipse that was sitting at a red light. The Mitsubishi’s driver, Alan McCrea, saw the bus in his mirror and hit the accelerator, but he was too late.

The Mitsubishi was knocked almost 100 yards, and McCrea suffered head and neck injuries.

The bus skidded 64 feet after the crash, and Matheson’s son suffered a gash to his lip and back injuries.

Matheson said she was told the bus had “bumped” a car. Now, 4½ years later, after she was shown photos from the accident, she was angry.

“I don’t know what to do about it now, but yeah, I feel slightly deceived – not slightly – I feel deceived,” she said.

Mark Hinson, chief human resource officer for Adams 12 Five Star Schools, said he could not speak to what Matheson had been told.

Hinson said the district has drug and alcohol testing requirements and training regiments that exceed requirements and that it takes other steps, such as forcing drivers to check in face-to-face with a supervisor each day, in the effort to ensure safe transportation.

“We’re transporting about 8,800 kids a day,” he said. “Our buses will complete somewhere between 1.3 and 1.6 million miles on the road a year. And when you think about traffic conditions, congestion, road conditions, weather conditions, it’s not surprising that there are going to be accidents.”

Ritchey, the driver in the case of Matheson’s son, had been written up six times over her time with the district.

According to paperwork in her file, she was disciplined for speeding, for picking up a student who wasn’t at a bus stop and failing to use her emergency lights, for getting into a confrontation with parents in a loading zone outside a school, for stopping at a McDonald’s with a student on her bus, for failing to perform a pre-trip safety check, and for allowing a student to crawl up the steps of her bus rather than boarding him in his wheelchair.

For the crash, she was subject to additional training and monitoring, said district spokesman Joe Ferdani.

Matheson said the lack of discipline surprised her.

““There should be something,” she said.

Hinson said that Ritchey has now been with the district more than 20 years.

“This driver has any number of periods of time in employment – two years, three years – with no policy violations or infractions and consistently does a good job,” he said.

Although bus drivers can lose their licenses in certain circumstances – too many tickets in a short period of time, for instance – discipline is left up to each district.

So how many accidents are too many?

“I think our goal needs to be no accidents,” said the Department of Education’s Okes. “Obviously that is everybody’s ideal goal, that there would be no accidents. And we continue to evaluate our procedures and our policies and our rules and our regulations, to make sure they are the most safe – they provide the safest transportation.”