Lawmakers added a car safety provision to the infrastructure bill. But some say it still isn't enough.

Following a six-year CBS News investigation that revealed potential safety dangers in vehicle seats, legislation aimed at increasing the federal strength standard has been included in the $1 trillion bipartisan infrastructure bill. But its congressional backers say the proposed legislation needs to be stronger.

In a series of stories that began airing in 2015, CBS News revealed that when hit from behind, car front seats may collapse backwards and their occupants can be propelled — forcefully — into the rear seats where children usually sit.

Now, the proposed 2,702-page infrastructure bill includes two paragraphs that, if passed, would instruct the National Highway Traffic Safety Administration to draft a new regulation within two years that updates the decades-old standard for the strength of vehicle front seats. The secretary of transportation would then decide if it should be implemented and "establish a date for required compliance with the final rule not later than 2 motor vehicle model years after the model year during which the effective date of the rule occurs."

But some lawmakers say the language in the bipartisan bill doesn't go far enough. They argue it should, instead, mirror a version passed by the House of Representatives in July requiring the traffic safety administration to replace the current regulation within two years.

"I am pleased the Senate has included a provision requesting the Department of Transportation to finally update seat back integrity standard in the bipartisan infrastructure deal. But this change should be mandated, as it is in my legislation, the Modernizing Seat Back Safety Act," said Representative Kathleen Rice, who along with Representatives Jan Schakowsky and Diana DeGette, credited CBS News with prompting their legislative push to fix the issue. "This is a simple piece of legislation that will save lives and prevent countless tragedies."

Senator Ed Markey, who twice introduced legislation to change the safety standard that's been in place since the 1960s, agrees.

"Thankfully, there are some important reforms," Markey told CBS News. "However, we must still fight to improve this bill before it becomes law. That's why I will be offering several amendments to strengthen my existing safety provisions."

Senator Richard Blumenthal, who joined fellow Democrat Markey in re-introducing safety legislation earlier this year, also believes the current legislation isn't enough.

"I will fight to strengthen these measures during the amendment process," Blumenthal said.

CBS News identified more than 100 people, mostly children, who were severely injured or killed in alleged seat back failures over the past 30 years. The number is likely higher: In 2016, then-NHTSA administrator Mark Rosekind acknowledged that such crashes were not closely tracked. 

Some estimates have put the death toll at closer to 50 Americans a year. 

One of those killed was Taylor Warner, who would have turned 12 in June. She was 16 months old and strapped into her car seat when her family's minivan was rear-ended. The force of the crash caused her father's seat to break and collapse backward into Taylor.

Her parents, Andy and Liz Warner, have spent years advocating for a new seat strength standard.

"I've always thought of this as a way to make sure she doesn't die in vain," Andy Warner said.

Crash tests have shown the risks associated with seat back failures for decades, with problems existing in many different car makes and models. Auto safety experts blame an outdated seat back safety standard.

The National Highway Traffic Safety Administration does not comment on proposed legislation.