Securing the driver's visual environment is a priority of tunnel lighting design. Safety in the visual environment of the tunnel is determined predominantly by the visibilities of the preceding vehicles and any on-road obstacles. This study verifies that pro-beam lighting improves the visibility in an expressway tunnel. The authors investigated the necessary luminance ratio of objects to background road surface, at which drivers can recognize objects in a tunnel. The authors also investigated other lighting factors (such as equivalent veiling luminance and horizontal and vertical illuminance) and their relationship to visibility. On asphalt and concrete roads with the same background illuminance, the silhouette view was more visible than the reverse silhouette view. The visibility of both silhouette and reverse silhouette views increased with horizontal illuminance on the asphalt road. In the multiple regression analysis, the main factors for improving visibility in the tunnel were the luminance ratio.