Project h. e.r.o. 259 The evacuation order will be given at least 24 to 26 h prior to the arrival of a hurricane. This is based on the timeline of the 1999 evacuation [Intergraph 2001l Boats, trailers, and other large vehicles will be limited from entering the main evacuation routes. Being able to evacuate people should have a higher priority than evacuating property If we can get everyone on a road within 24 h and keep traffic moving at a reasonable speed, everyone should be at a safe zone within 25 to 26 h. This is based on our assumption of what a safe zone is and our assumption of average speed Developing the Mode Abstracted Flow Modeling Upon inspecting the evacuation route map, we decided that there are only nine evacuation routes. There appear to be more, but many are interconnected and in fact merge at some point. By identifying all bottlenecks, we separated out the discrete paths Using this nine-path map in combination with the county map, we con- structed an abstracted flow model with nodes for each county, merge point, and destination so as to translate our model into a form for computer use a Brief discussion of flow The flow F is equal the product of density and speed: F= ks [Winston 1994]. We can find the density k of cars per mile by dividing 1 mi=5, 280 ft by the sum C+hd, the length of a car plus headway distance(in ft),so 5280s F=k Using the fact that headway distance hd is speed s(ft/s)times headway time h(sec),we 5280s 5280 +ht Increasing s increases F. This result is exciting, because it shows that max- imizing flow is the same as maximizing speed. The graph of F versus s gives even more insight(Figure 1). Increases in speed past a certain point benefit F less and less. So we might sacrifice parts of our model to increase low speeds but not necessarily to increase high speedsProject H.E.R.O. 259 • The evacuation order will be given at least 24 to 26 h prior to the arrival of a hurricane. This is based on the timeline of the 1999 evacuation [Intergraph 2001]. • Boats, trailers, and other large vehicles will be limited from entering the main evacuation routes. Being able to evacuate people should have a higher priority than evacuating property. • If we can get everyone on a road within 24 h and keep traffic moving at a reasonable speed, everyone should be at a safe zone within 25 to 26 h. This is based on our assumption of what a safe zone is and our assumption of average speed. Developing the Model Abstracted Flow Modeling Upon inspecting the evacuation route map, we decided that there are only nine evacuation routes. There appear to be more, but many are interconnected and in fact merge at some point. By identifying all bottlenecks, we separated out the discrete paths. Using this nine-path map in combination with the county map, we con￾structed an abstracted flow model with nodes for each county, merge point, and destination, so as to translate our model into a form for computer use. A Brief Discussion of Flow The flow F is equal the product of density and speed: F = ks [Winston 1994]. We can find the density k of cars per mile by dividing 1 mi = 5,280 ft by the sum C + hd, the length of a car plus headway distance (in ft), so F = ks = 5280s C + hd . Using the fact that headway distance hd is speed s (ft/s) times headway time ht (sec), we have F = 5280s C + sht = 5280 C s + ht . Increasing s increases F. This result is exciting, because it shows that max￾imizing flow is the same as maximizing speed. The graph of F versus s gives even more insight (Figure 1). Increases in speed past a certain point benefit F less and less. So we might sacrifice parts of our model to increase low speeds but not necessarily to increase high speeds