Many applications in vehicular ad hoc networks (VANETs) are based on broadcast to disseminate information among vehicles. In conventional broadcast protocols, only one vehicle is scheduled to rebroadcast a message at a certain time to avoid collision among vehicles. In this paper, we derive the maximum temporal displacement required by the concurrent transmissions in VANETs and propose a Concurrent Transmission based Broadcast (CTB) protocol. The CTB includes two parts, broadcast in a street and broadcast at intersections. We divide the transmission range in the broadcast direction into many segments and schedule the concurrent transmissions of the forwarders in the same segment. In our protocol, even if some selected forwarders fail to receive the message, other forwarders having received the message can still rebroadcast it, which reduces the broadcast delay and increases the broadcast reliability. Simulation results show that our protocol is much faster and more reliable, compared to conventional broadcast protocols.