Physical Layer Security (PLS) presents a potential solution to secure and reliable communication in next-generation vehicular networks. This work investigates the impact of redundancy on PLS performance in short-packet transmissions, focusing on its interplay with blocklength allocation. Building on the concept of trading reliability for security, we propose a joint optimization of redundant bits and blocklength, aiming to optimize the secure-reliability performance. We provide the globally optimal solutions for the integer problem by deriving the boundary of the feasible set. To derive a more efficient solution, we offer analytical insights for efficiently solving the relaxed version of this problem by reformulating the problem into a convex one. The numerical results offer guidance in resource allocation, revealing the trade-off between reliability and security in the context of redundant bits.