The growing penetration of electric vehicles (EVs) and the popularity of fast charging stations (FCSs) have greatly strengthened the coupling of the urban power network (PN) and traffic network (TN). In this paper

a potential security threat of the PN-TN coupling is revealed. Different from traditional loads

a regional FCS outage can lead to both the spatial and temporal redistribution of EV charging loads due to EV mobility

which further leads to a power flow redistribution. To assess the resulting potential threats

an integrated PN-TN modeling framework is developed

where the PN is described by a direct current optimal power flow model

and the TN is depicted by an energy-constraint traffic assignment problem. To protect the privacy of the two networks

an FCS outage distribution factor is proposed to describe the spatial-temporal redistribution ratio of the charging load among the remaining FCSs. Moreover

to protect the security of the coupled networks

a price-based preventive regulation method

based on the spatial demand elasticity of the EV charging load

is developed to reallocate the charging load as a solution for insecure situations. Numerical simulation results validate the existence of the PN-TN coupling threat and demonstrate the effectiveness of the regulation method to exploit the spatial flexibility of EV loads.