Some road-pricing demonstrations use "value pricing," in which travelers ca
n choose between a free but congested roadway and a priced roadway. Recent
research has uncovered a potentially serious problem for such demonstration
s: second-best tolls may be far lower than those typically charged, and fro
m a welfare perspective, the latter map be worse than not pricing at all. T
hat research, however, assumes that all travelers are identical and it ther
efore neglects the benefits of product differentiation. Using a model with
two user groups, we find that accounting for heterogeneity in value of time
is important in evaluating constrained policies, and improves the relative
performance of policies that offer differential prices. (C) 2000 Academic
Press.