Western Hemisphere Travel Initiative Improvement Act of 2018 This bill establishes certain standards for U.S. passport applications. The Department of State shall adjudicate U.S. passport applications in an individualized, evidence-based manner based on an assessment of individual circumstances and evidence. An applicant's race, ethnicity, or ancestry may not be considered in such adjudicatory process. The bill requires that: an applicant establish U.S. citizenship or nationality by a preponderance of the evidence, and a determination that an applicant has not met such evidentiary burden state in writing the reasons for the determination and be provided to the applicant in a timely manner. A birth certificate signed by a person authorized under state law to sign such a document, or a previously-issued U.S. passport, shall constitute prima facie evidence of U.S. citizenship or nationality and, absent individualized evidence that a birth did not take place in the United States, shall satisfy the preponderance of the evidence standard.