Abstract

In many emerging economies, callers may abandon ambulance requests due to a combination of operational (small fleet size), infrastructural (long travel times) and behavioral factors (low trust in the ambulance system). As a result, ambulance capacity, which is already scarce, is wasted in serving calls that are likely to be abandoned later. In this article, we investigate the design of an ambulance system in the presence of abandonment behavior, using a two-step approach. First, because the callers’ actual willingness to wait for ambulances is censored, we adopt a Maximum Likelihood Estimator estimation approach suitable for interval censored data. Second, we employ a simulation-based optimization approach to explicitly incorporate customers’ willingness to wait in: (i) tactical short-term decisions such as modification of dispatch policies and ambulance allocations at existing base locations; and (ii) strategic long-term network design decisions of increasing fleet size and re-designing base locations. We calibrate our models using data from a major metropolitan city in India where historically 81.3% of calls were successfully served without being abandoned. We find that modifying dispatch policies or reallocating ambulances provide relatively small gains in successfully served calls (around 1%). By contrast, increasing fleet size and network re-design can more significantly increase the fraction of successfully served calls with the latter being particularly more effective. Redesigning bases with the current fleet size is equivalent to increasing the fleet size by 8.6% at current base locations. Similarly, adding 29% more ambulances and redesigning the base locations is equivalent to doubling the fleet size at the current base locations and adding 34% more ambulances and redesigning base locations is equivalent to a three-fold increase. Our results indicate that in the absence of changes in behavioral factors, significant investment is required to modify operational factors by increasing fleet size, and to modify infrastructural factors by redesigning base locations.

摘要

在许多新兴经济体中，呼叫者可能由于操作（车队规模小），基础设施（旅行时间长）和行为因素（对救护车系统的信任度低）的组合而放弃了救护车请求。结果，已经稀缺的救护车容量浪费在服务呼叫上，而这些呼叫以后可能会被放弃。在本文中，我们使用两步方法研究了存在遗弃行为的救护车系统的设计。首先，由于对呼叫者等待救护车的实际意愿进行了审查，因此我们采用了适合间隔审查数据的最大似然估计器估计方法。其次，我们采用基于仿真的优化方法来明确纳入客户的等待意愿：（i）战术上的短期决定，例如修改派遣政策和在现有基地的救护车分配；（ii）增加机队规模并重新设计基地位置的战略性长期网络设计决策。我们使用来自印度一个主要大城市的数据校准模型，该城市在历史上成功地为81.3％的呼叫提供了服务而没有被放弃。我们发现，修改调度策略或重新分配救护车在成功服务的呼叫中获得的收益相对较小（约1％）。相比之下，增加机队规模和重新设计网络可以更显着地增加成功服务呼叫的比例，后者尤其有效。重新设计具有当前机队规模的基地相当于将当前基地位置的机队规模增加8.6％。同样，增加29％的救护车并重新设计基地位置，相当于使当前基地的机队规模增加一倍；增加34％的救护车和重新设计基地位置，相当于增加三倍。我们的结果表明，在没有行为因素变化的情况下，需要大量投资来通过增加机队规模来修改运营因素，并通过重新设计基地位置来修改基础设施因素。