A school bus crash Monday in Chattanooga claimed the lives of five elementary school children, and left at least twenty students injured. Police have charged the driver, and say speed was likely a factor in the crash.

Like a fatal 2014 bus crash in Knox County that killed two students and a teacher's aide, the tragedy has renewed questions and calls about the safety of buses, and particularly, why there are no seat belts on school buses.

According to the National Highway Traffic Safety Administration (NHTSA), children don't need to buckle up on school buses because the strong, closely-spaced seats with energy-absorbing backs on school buses provide crash protection.

On average, about five children die every year inside a school bus compared to 37,000 deaths inside cars, according to federal reports.

"It's kind of just natural to think you're in a moving vehicle, you should have a seatbelt," Republican state Rep. Bill Dunn told 10News in 2014. "But buses are built differently. They have the padded seats. It almost builds a little capsule around the child and protects them."

Officials also say that school bus seat belts potentially hinder children from quickly evacuating in an emergency.

“It depends on what kind of accident you have,” said Knox County interim school superintendent Buzz Thomas earlier this year.. “If a school bus catches on fire as vehicles often do when they’re in crashes kids who are in seat belts have a harder time getting out. Or if a school bus ends up in, God forbid, water (the) kids can drown.”

After the 2014 crash in Knox County, the school system commissioned a study on bus safety to make sure they were doing everything they could to keep children safe.

Despite findings that showed that Knox County had double the number of crashes it should for a district of its size in the past decade, officials still maintain the buses are safer than cars.

“They’re bright yellow, they have a known route, a trained driver, you have side wall strength, you have roof strength, there are flashing lights, they are designed to be observed,” said Kris Poland, a senior biomechanical engineer who investigates crashes for the National Transportation Safety Board (NTSB), including the one in Knoxville. “People know how to act around them in most cases.”

Thomas told 10News in August that at this point, the school system doesn’t plan to put seat belts on the buses unless the NTSB make such a recommendation.

And that’s not going to happen – at least for now.

The reason is two-fold: Officials feel buses are safe right now, and seat belts are expensive.

Poland said buses are safe from front-end and rear-end crashes, which would push a child forward and into the high, padded seat where the weight is distributed over a large surface.

“They’re kind of in this compartmentalized cocoon,” Poland said. “The problem happens in side impacts or rollovers.”

There’s no so-called cocoon to protect a child from traveling the width of a bus that’s been hit from the side. That’s where a seat belt would provide the most protection – by keeping the child in place. In Knoxville’s case, officials don’t know if seat belts would have helped the victims, since no video from the crash was available.

Still, the NTSB has not pushed for seatbelts on buses.

Poland said federal officials recognize that not all districts can afford to install seat belts on all buses.

“One of the things that we don’t want to have happen is that fewer buses are purchased and less children ride on school buses because we recognize that school buses are the safest way to go to and from school,” she said. “We’re very cautious. We don’t want to have any unintended negative consequences.”

State records suggest that each bus would cost $13,000 to retrofit. For Knox County’s 350 buses that would be $4.5 million.

And statewide, officials estimated the cost would be as much as $33 million per year for the next seven or so years, according to a fiscal report.

About half a dozen states have laws requiring safety restraints on school buses, and Tennessee's lawmakers have considered it numerous times over the years, but it has never passed.

In the wake of this most recent crash, a Chattanooga lawmaker said Tuesday he has started the process to draft legislation that would require seatbelts in all school buses in the state.

Although the details of legislation are still being considered, Rep. Gerald McCormick,said he is leaning toward a bill that would require retrofitting every single school bus in the state.

“I know it’s expensive but that’s the biggest budget item we have in the state – education – and if we can’t guarantee or do as much as we can to guarantee the safety of these kids as they go to and from school then the rest of it is pretty useless,” McCormick said.

Discussing how soon he would like to see the school buses retrofitted, which McCormick admitted would likely cost somewhere in the millions, he said he would like to see it done by next fall.