Connected vehicles extend the capability of information collection, and thus open more opportunities for innovative advanced driver assistance systems (ADAS). In this paper, we propose a Lane Speed Monitoring (LSM) application based on vehicle-to-vehicle (V2V) communication. This application takes advantage of Basic Safety Messages (BSM) transmitted from equipped vehicles via dedicated short range communication (DSRC), to estimate the real-time traffic states at the lane level. It then provides the driver with a recommendation on the optimal lane selection in terms of traffic conditions. A comprehensive simulation study has been conducted to evaluate the performance of this application, including safety, mobility, and environmental impacts, under various scenarios. Results indicate that the LSM application is beneficial to the individual user even under a low market penetration rate. Vehicles equipped with the application demonstrate up to 11% average speed improvement.