In Vehicular Ad-hoc NETwork (VANET), a Modified Decentralized Adaptive Time Division Multiple Access (TDMA) Scheduling mechanism (MDATS) is proposed by combining distributed TDMA and Space Division Multiple Access (SDMA) in order to solve the problem of contention collision when multiple nodes access channels simultaneously. The nodes with MDATS protocol, obtain the time slot allocation of two-hop neighbors through Frame Information (FI), which can determine the available time slot set. Then, the competition zone will be divided into several logical sections based on the number of available time slots. The nodes competitively select their time slots based on the mapping between the logical sections and the available time slots. This protocol reduces the contention collision among the nodes which access the channel simultaneously by the spatial dispersion of the available time slots. The simulation results show that MDATS protocol can achieve higher channel access success rate, lower access delay, and higher time slot utilization rate when it is compared with other similar MAC protocol.