  The concept of resilience can be realized in natural and engineering systems,
representing the ability of system to adapt and recover from various
disturbances. Although resilience is a critical property needed for
understanding and managing the risks and collapses of transportation system, an
accepted and useful definition of resilience for urban traffic as well as its
statistical property under perturbations is still missing. Here we define city
traffic resilience based on the spatio-temporal clusters of congestion in real
traffic, and find that the resilience follows a scale free distribution in
two-dimensional city road networks and one-dimensional highways, with different
exponents, but similar exponents in different days and different cities. The
traffic resilience is also revealed to have a novel scaling relation between
the cluster size of the spatio-temporal jam and its recovery duration,
independent of microscopic details. Our findings of universal traffic
resilience can provide indication towards better understanding and designing
these complex engineering systems under internal and external disturbances.
