This paper considers the modeling of road congestion subject to peak-load demand. The standard model contains ambiguities and is poorly specified. These problems can be eliminated by working with a structural model that explicitly treats the congestion technology and drivers' behavioral decisions. The paper provides a detailed analysis of a particular structural model--William Vickrey' s model of bottleneck congestion in the morning rush-hour auto commute extended to treat elastic (i.e., price-sensitive) demand--and examin es some economic implications of the structural approach.

Factors display strong cross-sectional momentum that subsumes momentum in industries and other portfolio characteristics. The profits of all these momentum strategies—based on factors, industries, and other characteristics—significantly correlate with each other and therefore likely emanate from the same source. If factors display momentum, so will any set of portfolios with cross-sectional variation in factor loadings. Consistent with factors being at the root of momentum, we find that momentum in industry-neutral factors explains industry momentum, but industry momentum explains none of the factor momentum. Cross-sectional factor momentum concentrates in the first few highest-eigenvalue factors and is distinct from time-series factor momentum.