Wireless Mesh Networks (WMNs) are broadly used recently, due to its flexibility, reliability and robust services. IEEE 802.11s defines Hybrid Wireless Mesh Protocol (HWMP) as the default routing protocol for WMNs and airtime link metric as the default path selection metric. Airtime metric can collect the channel information from both PHY and MAC layers to estimate average latency per packet transmission through a link, but it typically suffers from several shortcomings, such as ignoring the influence of traffic flow and inefficient usage of the shared wireless resources. In this paper, we propose a modified HWMP protocol with an enhanced airtime metric called as HWMP+, which can estimate the link quality in combination with traffic flow information and allocate the network resources in an efficient way. The proposed metric computation procedure has both historical and real-time perspectives of the link quality and is more sensitive to the link quality variations, especially in a dynamic topology. We also improve the routing scheme and optimally manage the shared channel resources according to the traffic flow information. Simulation results using Qualnet 5.0 show that, the proposed schemes can considerably improve the system performance, in terms of network throughput and average end-to-end delay.