Preclearance allows all necessary customs and immigration inspections to be completed before departure, while the traveller is still in Canada, and the powers that U.S. border officers exercise under Canadian law are governed by the Canadian Bill of Rights, the Canadian Human Rights Act and the Canadian Charter of Rights and Freedoms.
Proponents say preclearance will facilitate the flow of people and goods between the US and Canada. Under preclearance, a traveller passes through US customs in Canada, so they do not need to do so once they enter the US, and vice-versa. There are US preclearance areas in eight Canadian airports, along with some train and ferry crossings in BC, and plans to expand this to more Canadian airports and train stations. Canadian preclearance zones would also be established for the first time in the United States.