This document discusses challenges and opportunities in smart transportation research under smart cities. It outlines how transportation is a major issue impacting environment, safety, and public health. Smart cities and transportation big data can help address key issues of efficiency, sustainability and safety through data analytics. The document presents examples of extracting transportation data from mobile networks and DRIVE Net, a system for data sharing, visualization, and analysis to support e-science investigations in transportation. Research needs include developing methods to utilize spatial and temporal big data to support analysis and decision making in transportation.