Key takeaways
- Underride defeats the safety systems in your car. When the point of impact is the trailer deck rather than your bumper, the sensors that fire airbags and the structure that absorbs energy are both bypassed.
- The rear guard rule was upgraded in 2022. NHTSA amended FMVSS 223 and 224 so guards must prevent passenger compartment intrusion at 35 mph rather than the previous 30 mph design point.
- Side guards remain unregulated. Congress directed NHTSA to research them and convene an advisory committee. As of 2026 no federal side underride guard requirement is in force.
- The trailer is a separate defendant. Tractor and trailer are often owned, maintained, loaded, and insured by different companies, and the one at fault may not be the one whose name is on the door.
This guide is written and reviewed by our editorial team to be accurate and current. It is general information, not legal advice, and reading it does not create an attorney-client relationship. Federal safety rulemaking on underride protection is active and changing, so confirm the current position with a licensed attorney in your state. If you are facing an emergency, call 911.