The expansion of 802.11 AP deployments provides opportunistic Wi-Fi access in underground Mass Rapid Transit (MRT) system. However, such vehicular network faces the challenge of limited time for the MS on the train to connect the base station at the station. Therefore, to maximize the throughput within these several tens of seconds becomes crucial to the network. To achieve this goal, the authors propose Accelerometer-Assisted Rate Adaptation (AARA), a mechanism utilizes the out-of-band information of a train's acceleration to improve the conventional rate adaptation scheme. AARA consists of two parts: First, AARA divides a train's movement into four phases and performs real-time estimation on the train's current movement phase.