<p>The communication based train control (CBTC) systems is now facing multiple threats of cyber attacks. Intrusion detection systems (IDS) are deployed to deal with the increasing number of attack scenarios by analyzing system behavior and generating alerts. However, a single IDS may suffer a single point of failure and cannot cope with complex cyber attacks. Therefore, collaborative intrusion detection systems (CIDS) are introduced to address these weaknesses. The key challenges in the research of CIDS are how to establish trust and build consensus among the participating CIDS nodes. In this paper, we propose an enhanced blockchain-based collaborative intrusion detection systems to protect train control systems from cyber attacks, especially against insider attacks like betrayal attacks and Sybil attacks. Specifically, a three-step trust evaluation mechanism is designed to deal with the trust challenge caused by insider attacks, which consists of the response to attacks, the node importance weight assignment and the trust score aggregation. Then, a hybrid consensus algorithm based on the accuracy of attack detection and the trust score of the CIDS node is proposed. Specifically, the real-time performance and historical performance of CIDS nodes are used to control the difficulty of consensus reaching among nodes, with the purpose of improving the efficiency of block generation. The simulation experiments show that our enhanced blockchain-based collaborative intrusion detection approach has great advantages in improving the sensitivity of trust evaluation and the efficiency of consensus reaching.</p>