  Urban transportation systems are vulnerable to congestion, accidents,
weather, special events, and other costly delays. Whereas typical policy
responses prioritize reduction of delays under normal conditions to improve the
efficiency of urban road systems, analytic support for investments that improve
resilience (defined as system recovery from additional disruptions) is still
scarce. In this effort, we represent paved roads as a transportation network by
mapping intersections to nodes and road segments between the intersections to
links. We built road networks for 40 of the urban areas defined by the U.S.
Census Bureau. We developed and calibrated a model to evaluate traffic delays
using link loads. The loads may be regarded as traffic-based centrality
measures, estimating the number of individuals using corresponding road
segments. Efficiency was estimated as the average annual delay per peak-period
auto commuter, and modeled results were found to be close to observed data,
with the notable exception of New York City. Resilience was estimated as the
change in efficiency resulting from roadway disruptions and was found to vary
between cities, with increased delays due to a 5% random loss of road linkages
ranging from 9.5% in Los Angeles to 56.0% in San Francisco. The results
demonstrate that many urban road systems that operate inefficiently under
normal conditions are nevertheless resilient to disruption, whereas some more
efficient cities are more fragile. The implication is that resilience, not just
efficiency, should be considered explicitly in roadway project selection and
justify investment opportunities related to disaster and other disruptions.
