  Understanding the long-term impact that changes in a city's transportation
infrastructure have on its spatial interactions remains a challenge. The
difficulty arises from the fact that the real impact may not be revealed in
static or aggregated mobility measures, as these are remarkably robust to
perturbations. More generally, the lack of longitudinal, cross-sectional data
demonstrating the evolution of spatial interactions at a meaningful urban scale
also hinders us from evaluating the sensitivity of movement indicators,
limiting our capacity to understand the evolution of urban mobility in depth.
Using very large mobility records distributed over three years we quantify the
impact of the completion of a metro line extension: the circle line (CCL) in
Singapore. We find that the commonly used movement indicators are almost
identical before and after the project was completed. However, in comparing the
temporal community structure across years, we do observe significant
differences in the spatial reorganization of the affected geographical areas.
The completion of CCL enables travelers to re-identify their desired
destinations collectively with lower transport cost, making the community
structure more consistent. These changes in locality are dynamic, and
characterized over short time-scales, offering us a different approach to
identify and analyze the long-term impact of new infrastructures on cities and
their evolution dynamics.
