Static traffic models, in the tradition of Walters (1961), typically feature a ‘‘demand curve’’ giving the vehicle flow demanded for each unit travel time (inverse speed). Traditionally, the demand curve declines because people want to drive more as travel times fall. This paper proposes that the vehicle flow demanded can, instead, plausibly rise with unit travel time (a phenomenon we call ‘‘hyperdemand’’), if congestion somehow induces some people to switch from high-to low-occupancy modes. To illustrate, we present a model of travel in an isotropic downtown where people choose among not traveling, a low-occupancy mode called ‘‘Alone’’ and a high-occupancy mode called ‘‘Pool.’’ Pool trips detour to pick up and drop off passengers en route, so congestion delays them more than Alone trips. Consequently, multiple equilibria can arise even in ‘‘light congestion,’’ and small toll increases can have dramatic impacts by eliminating equilibria.

按照沃尔特斯（Walters，1961）的传统，静态交通模型通常具有“需求曲线”，给出了每个单位行驶时间（倒车速度）所需的车辆流量。传统上，需求曲线会下降，因为人们希望随着出行时间的减少而开车更多。本文提出，所需的车辆流量反而可能上升如果单位交通时间（一种我们称之为“超需求”的现象）出现，则交通拥堵会导致某些人从高占用模式切换到低占用模式。为了说明这一点，我们提出了在各向同性的市区旅行的模型，人们在其中选择不旅行，即低占用模式“ Alone”和高占用模式“ Pool”。泳池旅行绕道而行并在途中下车，所以交通拥堵比单独旅行延迟更多。因此，即使在“轻度拥堵”中也可能出现多重均衡，通行费的小幅增长可能会消除均衡而产生巨大影响。