Contents lists available at ScienceDirect Transport Policy journal homepage: www.elsevier.com/locate/tranpol Long-term lessons on the effects of post-9/11 border thickening on cross- border trade between Canada and the United States: A systematic review Matthew J. Smith, Sayan Basu Ray, Aaron Raymond, Micah Sienna, Meredith B. Lilly * Associate Professor and Simon Reisman Chair in International Affairs, Norman Paterson School of International Affairs, Carleton University, 5109 Richcraft Hall, Ottawa, ON K1S 5B6, Canada ARTICLE INFO Keywords: 9/11 Border thickening Canada-US Trade flows Border security ABSTRACT Following the terror attacks on the United States in September 2001, the country briefly closed all borders. The consequences for cross-border trade with Canada were swift and immediate. Following more than a decade of efforts by trade and transportation policymakers in both countries to facilitate greater economic integration and cross-border trade since 9/11, the US administration under Donald Trump may again seek to thicken its border with Canada. This systematic review evaluates 13 years of research on the consequences of post-9/11 border thickening on Canada-US trade and commercial relations. Applying rigorous methods for the conduct of sys- tematic reviews, 19 studies were included in the final analysis and grouped into four analytic themes: aggregate trade, sector, region, and passenger flows. We find that overall bilateral trade was negatively impacted following 9/11 but Canadian economic interests were harmed more seriously than those of the US. We also find differing consequences for cross-border flows according to region, sector and firm size. In addition, efforts focused on border transport policies to mitigate these consequences were effective but underutilized, especially in regions and sectors that did not depend on cross-border integration. Our findings offer important long-term lessons for policymakers on both sides of the border. 1. Introduction The Canada-United States (US) border is both the world's longest and most economically active. Every day, upwards of $2.4 billion USD in goods and services and 400,000 people cross the Canada-US border (Government of Canada, 2017). The Canadian government estimates that trade with the US supports 3.3 million jobs in Canada and as many as 9 million jobs in the US (Government of Canada, 2017). Despite having a balanced bilateral trading relationship valued at approxi- mately $628 billion (USD) annually, Canada is much more dependent on trade with the US than vice versa. For example, the $308 billion (USD) in Canadian exports to the US in 2016 accounted for three- quarters of all Canadian exports globally, while the $320 billion (USD) in American exports to Canada represented only 16% of total US ex- ports (USTR, 2016). Thus, although smooth and efficient cross-border trade is important to both economies, Canada is uniquely vulnerable to border slowdowns and closures. The terrorist attacks of September 11th, 2001 dramatically altered US policy on border security for a generation. Following the terror at- tacks on September 11th, the United States closed all airports, seaports, and land ports with Canada and Mexico. This reverberated throughout the Canadian economy since, in one fell swoop, Canada's largest trading partner had shut off access. Upon reopening of the border several days later, passenger cars, travellers, and transport trucks seeking to enter the United States were subject to lengthy inspections and border delays. In some instances, transport trucks were delayed for up to 18 h (Globerman and Storer, 2008). Hale (2011) has outlined how increasing cross-border efficiency resulting largely from expanded trade under the North American Free Trade Agreement (NAFTA) suddenly became a secondary goal to se- curitization following 9/11. For instance, Hale documents how the pre- 9/11 policy emphasis on “shared borders” (28) and the “facilitative” (29) functions of border management shifted following 9/11 toward an American-led “sovereign” approach to border “control” (34). Hale goes on to emphasize how this securitization policy permeated all areas of government policy making from environmental management to cultural policy (Hale, 2011). The risks to business and trade associated with border delays arising from such securitization efforts quickly became apparent. To address these trade disruptions, the Canadian and US governments signed the https://doi.org/10.1016/j.tranpol.2018.03.013 Received 10 October 2017; Received in revised form 9 February 2018; Accepted 29 March 2018 * Corresponding author. E-mail addresses: MattJSmith@cmail.carleton.ca (M.J. Smith), SayanBasuRay@cmail.carleton.ca (S.B. Ray), AaronRaymond@cmail.carleton.ca (A. Raymond), micahsienna@cmail.carleton.ca (M. Sienna), @lillyresearch, Meredith.lilly@carleton.ca (M.B. Lilly). Transport Policy xxx (xxxx) xxx–xxx 0967-070X/ © 2018 Elsevier Ltd. All rights reserved. Please cite this article as: Smith, M.J., Transport Policy (2018), https://doi.org/10.1016/j.tranpol.2018.03.013