Wireless vehicular ad hoc networks are characterized by multi-hop transmission, where a key problem is the design of routing, e.g., how to efficiently direct the information flow from the source to the destination via available intermediate nodes. In this paper, cross-layer routing is studied by applying cooperative transmission and a new strategy of path selection is proposed to achieve a better tradeoff between the transmission power consumption and end-to-end reliability. The influence of cooperative transmission to the wireless link cost is first studied, which shows that the quality of wireless links could be improved significantly. Then we focus on formulating the objective functions for the addressed cross-layer optimization problem. Specifically, according to different quality of service requirements, two different types of routing optimization are investigated to understand the effects of improved link cost to the routing decision. The closed-form expressions of the optimal solutions for two addressed optimization problems are developed and later used as quantitative criteria of the routing decision. Our developed analytical and simulation results show that the criteria using cooperative transmission typically yield more efficient routes than the comparable schemes in terms of end-to-end reliability and total transmission power.