The deregulation of the taxicab industry has largely been debated for perceived customer benefits resulting from lower wait times and fares. More often than not, the negative externalities, i.e. traffic congestion and tailpipe emissions, are ignored in discussions related to deregulation. This report focuses on the possible adverse impacts (traffic congestion and tailpipe emissions) resulting from an increase in taxicab fleet size in a post-deregulated taxicab industry. Research on taxicab deregulation shows that an increase in the number of motorized vehicles on a congested road network is likely to worsen traffic congestion and increase tailpipe emissions. In this regard, Toronto, a heavily congested city, is likely to experience increased traffic congestion resulting from increased motorization. These outcomes are a function of total vehicle travel and fuel efficiency and are related to the size of the vehicle fleet and availability of transportation alternatives. Higher vehicle ownership rates have historically been associated with both higher transportation energy consumption per capita (Newman and Kenworthy, 2006) and greater emissions from vehicle production: there were nearly 17 million new vehicles sold in the U.S. in 2018, each generating nearly 8 metric tons of GHGs from the manufacturing process (Davis et al., 2019) (Figure S1). The introduction of TNC services could disrupt the relationship between vehicle ownership and transportation energy consumption and emissions not only in the U.S. but also globally, including in countries like China and India, where vehicle registration numbers are climbing more than 10% each year (Davis et al., 2019).