探讨了各方式的服务属性变化对方式选择转换的影响和引起选择变化的临界状态．通过提出临界期望效用的概念，运用多属性决策理论，引入标量场梯度，结合空间解析几何的方法，基于 Probit 模型推导了临界值的计算公式，刻画了该临界平衡状态对各属性参数的相依性;最后以一条简单的通勤线路为例，根据所推算的临界属性，针对该线路中公交和小汽车方式选择的转换问题，提出几种策略并设计两种评价指标对其进行对比分析．研究结果对交通政策的制定和调整有一定的参考意义．

This article probes into the effects of service attribute variation on mode choice transfer and the criticalstate giving rise to mode choice transfer.Through putting forward the concept of critical expectant utility,usingmulti- attribute decision- marking theory,introducing the gradient theory into scalar field and combining the spatialanalytical geometry method,the computational formulas for solving the critical values are derived on the basis of theProbit model.Then,the dependency of the critical balance upon each attribute parameter is described.Finally,according to the computed critical properties,the transfer of public transportation mode (by bus or by car) is ana-lyzed by taking a simple commuting line as the example,with several strategies and two evaluating indicators beingproposed and compared.This research has certain referential value on the formulation and adjustment of transportpolicy.