The "Stop Underrides Act 2.0" seeks to significantly reduce fatalities and injuries resulting from underride crashes involving commercial motor vehicles. It addresses a critical public safety concern by mandating enhanced underride protection systems on trailers, semitrailers, and single unit trucks, aiming for more survivable truck crashes and improved safety for all road users. A core provision of the bill requires the Secretary of Transportation to finalize regulations within 18 months for new or updated motor vehicle safety standards. These standards will mandate the installation of side underride guards on new trailers, semitrailers, and single unit trucks. The guards must prevent intrusion into passenger vehicle occupant survival space during perpendicular impacts up to 40 miles per hour, impede vulnerable road users from sliding underneath, and incorporate aerodynamic designs for fuel efficiency. The legislation also strengthens the Advisory Committee on Underride Protection by requiring its reconvening, expanding its membership to include underride crash victims' families, and increasing its meeting frequency. Furthermore, it directs the creation of a publicly accessible website to serve as a comprehensive repository for underride research, reports, and victim stories, updated quarterly. To improve data and understanding, the bill mandates two key studies. The National Academies of Sciences, Engineering, and Medicine (NASEM) will study the prevalence of front underride crashes and recommend prevention strategies. Concurrently, the Government Accountability Office (GAO) will assess the implementation of existing rear impact guard regulations and suggest improvements. Finally, the bill requires the National Highway Traffic Safety Administration (NHTSA) to conduct a review of the Fatality Analysis Reporting System (FARS) to identify underreported underride crashes and recommend improvements for incident reporting. NHTSA must also develop free, web-based training for State and local law enforcement to properly identify and document underride crashes, ensuring more accurate data collection.