Vehicular Ad Hoc Networks (VANETs) necessitate secure and seamless authentication across administrative domains in the era of intelligent transportation systems. In dynamic systems characterized by substantial vehicle mobility, conventional cross-domain authentication methods typically exhibit single points of failure, elevated communication and computation costs. We propose a Blockchain-based Cross-Domain Authentication Protocol for decentralized, tamper-resistant, immediate vehicle authentication to address these limitations. To ensure the security and computational efficiency of our protocol, we utilize the Elliptic Curve Digital Signature Algorithm (ECDSA) for the formulation and verification of digital signatures, and Elliptic Curve Cryptography (ECC) for efficient key generation. The proposed solution allows direct authentication via blockchain during cross-domain transitions. A consortium blockchain is essential for enabling cross-domain authentication for vehicles and other domain Roadside Units (RSUs). This approach reduces communication cost by 14.97 % and computation costs relative to existing solutions. The Scyther tool facilitates formal verification to ensure the protocol’s correctness and it is resilient against common threats such as replay attacks, man-in-the-middle attacks, and impersonation attacks.