How to evaluate the comprehensive costs and benefits of urban light trains is a critical issue. The difference-in-differences technique is widely used in the literature. However, the conventional approach assumes the project does not affect the control group, which might be violated in real life due to social and economic interactions. We refine the DID approach and relax the no-spillover assumption. Through an example of impacts of a new light rail transit on house prices in Edmonton, Canada, we illustrate how the approach can be used to calculate three different treatment effects. The results indicate that the train system has negative impacts on values of single-detached houses nearby the train stations, and the negative effects also spill over to properties outside the treatment zone. Our findings show that the direction and magnitude of project impacts depend on the city size, the design of the train system, and relevant neighborhood characteristics.

如何评估城市轻轨的综合成本和收益是一个关键问题。差异差异技术在文献中得到了广泛的应用。但是，常规方法假定项目不影响对照组，而在现实生活中，由于社会和经济的相互作用，该组可能会受到侵犯。我们完善DID方法并放宽无溢出假设。通过一个新的轻轨交通对加拿大埃德蒙顿房价的影响的例子，我们说明了如何将该方法用于计算三种不同的治疗效果。结果表明，火车系统对火车站附近的单栋房屋的价值产生了负面影响，并且负面影响还蔓延到治疗区以外的物业。