With the emergence of intelligent transportation, VANETs have received more and more attention. The dynamic topological structure of VANETs changes sharply, which makes high demands on network performance, such as the throughput rate and transmission rate. We propose an adaptive multichannel dual clock NPCSMA random multiple access protocol with RTS/CTS mechanism. We first define two kinds of PCSMA protocols. The RTS/CTS mechanism solves the hidden terminal problem, the dual clock mechanism reduces average idle time, and the multichannel mechanism increases channel number, identifies priorities of users and improves the throughput rate. The adaptive mechanism enables the system to maintain stable throughput rate under high load. We also analyze transmission rate, which is proved to be relatively high. The calculation formulas of throughput rate and transmission rate are derived through the average period method, and the simulation results are consistent with the theoretical derivation.