We are living in the 21st century in which technological advances have greatly improved the quality of human lives. However nature keeps presenting its challenges in the form of tsunamis, floods, wild fires, hurricanes, volcanoes, etc. Excellent evacuation route planning is of paramount importance to reduce loss of lives during such disasters. The parameters of finite time lined capacity of evacuation paths and thousands to millions of evacuees for the problem of evacuation route planning makes it more complex than the problem of finding the shortest path which has been studied extensively in graph theory. Computation time (execution time hereafter) and evacuation time are two key properties which determine the efficiency and effectiveness of evacuation routing algorithms. This paper proposes a graph theory based evacuation routing algorithm called Forward Backward Shortest Path (FBSP). FBSP uses a novel idea to determine multiple routes by combining multiple paths at a time unlike other evacuation routing algorithms such as Shortest Multiple Path (SMP) that uses just the shortest paths between the source nodes and destination nodes. The experimental analysis on simulated graphs showed that FBSP improves evacuation time over SMP without significantly increasing execution time.