Schmid Verena, Doerner Karl F
Department of Business Administration, University of Vienna, Bruenner Strasse 72, 1210 Vienna, Austria.
Eur J Oper Res. 2010 Dec 16;207(3):1293-1303. doi: 10.1016/j.ejor.2010.06.033.
how and where to locate vehicles in order to cover potential future demand effectively. Ambulances are supposed to be located at designated locations such that in case of an emergency the patients can be reached in a time-efficient manner. A patient is said to be covered by a vehicle if (s)he can be reached by an ambulance within a predefined time limit. Due to variations in speed and the resulting travel times it is not sufficient to solve the static ambulance location problem once using fixed average travel times, as the coverage areas themselves change throughout the day. Hence we developed a multi-period version, taking into account time-varying coverage areas, where we allow vehicles to be repositioned in order to maintain a certain coverage standard throughout the planning horizon. We have formulated a mixed integer program for the problem at hand, which tries to optimize coverage at various points in time simultaneously. The problem is solved metaheuristically using variable neighborhood search. We show that it is essential to consider time-dependent variations in travel times and coverage respectively. When ignoring them the resulting objective will be overestimated by more than 24%. By taking into account these variations explicitly the solution on average can be improved by more than 10%.
如何以及在何处定位车辆，以便有效地满足未来潜在的需求。救护车应停在指定地点，以便在紧急情况下能及时到达患者身边。如果患者能在预定义的时间限制内被救护车送达，则称该患者被一辆车辆覆盖。由于速度变化以及由此产生的行驶时间不同，仅使用固定的平均行驶时间一次性解决静态救护车定位问题是不够的，因为覆盖区域本身会在一天中发生变化。因此，我们开发了一个多时段版本，考虑到随时间变化的覆盖区域，我们允许车辆重新定位，以便在整个规划期内维持一定的覆盖标准。我们针对手头的问题制定了一个混合整数规划，试图同时优化不同时间点的覆盖情况。该问题使用可变邻域搜索以元启发式方法求解。我们表明，分别考虑与时间相关的行驶时间和覆盖区域变化至关重要。忽略这些变化时，最终目标将被高估超过24%。通过明确考虑这些变化，平均而言，解决方案可提高超过10%。
