The National Environmental Policy Act (NEPA) of 1970 requires federal agencies to assess the environmental impact of proposed federal actions. NEPA thus affects delivery of a wide range of infrastructure projects. NEPA requires the completion of an Environmental Impact Statement (EIS) for environmentally impactful federal actions. For infrastructure projects this can entail significant delays. A typical EIS now takes about four and one-half years and is over 600 pages long. Some EIS’s take over a decade to complete. We provide the first detailed analysis of project approval times under NEPA by examining 1269 EIS permitting processes. We analyze empirically the well-defined interval from Notice of Intent to file to Record of Decision (ROD). We use a Cox proportional hazard model to estimate the impact of several factors on EIS duration. Factors include permits featuring major construction, those including private investment, those for projects located in states with restrictive environmental laws, those using the federal permitting “dashboard,” and those publishing a Supplemental EIS prior to the ROD. We find that privately financed projects receive faster permitting, while projects involving major construction, those undertaken in restrictive states, and those utilizing the federal permitting dashboard, face slower permitting times. We also explore links between EIS page counts and permitting time. Greater EIS page counts are associated with longer permitting times. We conclude by examining EIS completion during economic stimulus programs such as the American Recovery and Reinvestment Act (ARRA), as well as the frequency of EIS completion by the federal government.