Which agency is primarily responsible for setting federal highway regulations?

The Federal Highway Administration (FHWA) is the agency primarily responsible for setting federal highway regulations. Established within the U.S. Department of Transportation, the FHWA focuses on ensuring the nation's highway systems are safe, efficient, and environmentally sustainable. The agency develops policies and guidelines that govern highway design, construction, and maintenance, and it provides funding and oversight to state and local transportation agencies.

The FHWA also plays a key role in establishing safety standards, managing federal funding for highway construction, and promoting innovations in highway safety practices. This comprehensive approach aids in maintaining a consistent regulatory framework that impacts the operation of highways across the nation, ensuring that safety and efficiency are prioritized.

In contrast, the other agencies mentioned in the options have different roles. The Federal Highway Commission is not a functioning body but rather a historical reference to earlier highway governance. The Transportation Safety Board and the National Transportation Safety Board both deal with broader transportation safety issues, including investigations and recommendations across various modes of transportation, but they do not set federal highway regulations specifically. Thus, the FHWA stands out as the authoritative body for this domain.