AODV routing protocol can not take full advantage of the multi-interface technology to balance load and reduce flow interference since it uses hop counts as routing metric. To solve this problem, we propose a novel routing metric for multi-interface wireless mesh networks in this paper, which is named Cumulative Load Transmission Time (CLTT) metric. This metric can capture the load interference, packet loss ratio and transmission rate. Based on the AODV protocol, we present a new routing protocol, called AODV-CLTT, which uses the CLTT metric to select routes with lower interference. The simulation results show that the AODV-CLTT protocol outperforms the AODV protocol in terms of the average throughput and the end-to-end delay.