Directional broadcast was proposed in VANETs in order to disseminate data to other vehicles efficiently. However, traditional directional broadcast protocols cannot provide good enough efficiency for VANETs, especially in the urban area. In this paper, we propose an efficient road-based directional broadcast protocol for VANETs in urban environment. We avoid misclassification problem that traditional directional broadcast protocols have by selecting relay nodes based on which roads they are on. In addition, due to obstacles in urban area, the inter-vehicle communication at an intersection is unreliable. To increase the chance of propagating data toward all directions at an intersection, our protocol classifies vehicles into groups based on road, and selects a relay node with the best line-of-sight for each group. Simulations show that our approach has better efficiency and reliability than existing broadcast protocols.