This paper explores how to build an efficient regional alert system by using bidrectional traffic and maintaining a perimeter intelligently for a single alert. We demonstrated that our protocol BiPP is efficient in propagating an alert. For practical purposes, BiPP’s overhead is independent of the safety radius and car density. BiPP also performs superbly in notifying cars of the alert even when the communication range is very small. Moreover, BiPP’s overhead is within a small constant factor (typical within a factor of
C
) of IVG’s overhead while providing much stronger guarantees and tolerance for limited communication ranges.