  Recent research in the social sciences has identified situations in which
small changes in the way that information is provided to consumers can have
large aggregate effects on behavior. This has been promoted in popular media in
areas of public health and wellness, but its application to other areas has not
been broadly studied. This paper presents a simple model which expresses the
effect of providing commuters with carefully-curated information regarding
aggregate traffic "slowdowns" on the various roads in a transportation network.
Much of the work on providing information to commuters focuses specifically on
travel-time information. However, the model in the present paper allows a
system planner to provide slowdown information as well; that is, commuters are
additionally told how much slower each route is as compared to its uncongested
state. We show that providing this additional information can improve
equilibrium routing efficiency when compared to the case when commuters are
only given information about travel time, but that these improvements in
congestion are not universal. That is, transportation networks exist on which
any provision of slowdown information can harm equilibrium congestion. In
addition, this paper illuminates a deep connection between the effects of
commuter slowdown-sensitivity and the study of marginal-cost pricing and
altruism in congestion games.
