258 The UMAP Journal 22.3 (2001) Headway distance hd: the space between the back of the leading car and the front of the immediately trailing car(ft).(Note: This is not a standard defi nition of headway distance.) Headway time h: the time required to travel headway distance Car Length C: length from front bumper to rear bumper of a single car( feet) G oals Our first priority is to maximize the number of people who reach safety; in terms of our model, we must maximize the flow of the entire system. A secondary goal is to minimize the total travel time for evacuees; this means that we must maximize speed. As we establish, these goals are one and the same Assumptions Vehicles hold 2 people on average. This seems reasonable, based on the percentage of the population who would be unable to drive themselves and those who would carpool Vehicles average 17 ft in length. This is based on a generous average fol lowing a quick survey of car manufacturers Web sites Vehicles have an average headway time of 3 s. This is based on numbers for driver reaction time, found in various driving manuals 50 mph is a safe driving spee Merging of traffic does not significantly affect our model. See the Ap- pendix for justification Highways 26, 76/328, and 501 are 4-lane. [Rand McNally 1998 Safety is defined as 50 mi from the nearest coastal point. Counties that lie beyond this point will not be evacuated [SCAN21 20011 Only the following counties need to be evacuated: Allendale, Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Hampton, Horry, Jasper, Marion, Williamsburg, and a minimal part of Florence County(based on the previous assumption) Myrtle Beach will not be at its full tourist population during a hurricane warning. This seems reasonable because tourists do not like imminent bad weather.258 The UMAP Journal 22.3 (2001) Headway distance hd: the space between the back of the leading car and the front of the immediately trailing car (ft). (Note: This is not a standard defi- nition of headway distance.) Headway time ht: the time required to travel headway distance. Car Length C: length from front bumper to rear bumper of a single car (feet). Goals Our first priority is to maximize the number of people who reach safety; in terms of our model, we must maximize the flow of the entire system. A secondary goal is to minimize the total travel time for evacuees; this means that we must maximize speed. As we establish, these goals are one and the same. Assumptions • Vehicles hold 2 people on average. This seems reasonable, based on the percentage of the population who would be unable to drive themselves and those who would carpool. • Vehicles average 17 ft in length. This is based on a generous average fol￾lowing a quick survey of car manufacturersí Web sites. • Vehicles have an average headway time of 3 s. This is based on numbers for driver reaction time, found in various driving manuals. • 50 mph is a safe driving speed. • Merging of traffic does not significantly affect our model. See the Ap￾pendix for justification. • Highways 26, 76/328, and 501 are 4-lane. [Rand McNally 1998] • Safety is defined as 50 mi from the nearest coastal point. Counties that lie beyond this point will not be evacuated [SCAN21 2001]. • Only the following counties need to be evacuated: Allendale, Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Hampton, Horry, Jasper, Marion, Williamsburg, and a minimal part of Florence County (based on the previous assumption). • Myrtle Beach will not be at its full tourist population during a hurricane warning. This seems reasonable because tourists do not like imminent bad weather