To address the vehicle-to-vehicle (V2V) link failure caused by severe shadowing in vehicular networks, roadside-based intelligent reflecting surfaces (IRS) were considered to assist the V2V communications, and the outage performance of the vehicular networks with such communication mode was analyzed. Under the Rayleigh fading model, the closed-form expression and asymptotic expression of the outage probability for the perfect phase-shift IRS-assisted V2V communication were derived respectively. The closed-form expression of the outage probability for the non-perfect phase-shift IRS-assisted V2V communication was derived based on an approximate transformation of the moment generating function. Meanwhile, the co-channel interference caused by IRS to the nearby vehicle-to-infrastructure (V2I) communication was considered, and it was proved that the interference signal follows a zero-mean complex Gaussian distribution. Then the closed-form expression of the outage probability of the V2I communication was derived. Simulation results verified the correctness of the theoretical derivations and it was shown that, with minor phase shift error, IRS could effectively enhance the reliability of the V2V communication while causing extremely weak co-channel interference
