Safe Highways Act of 1998 - Directs the Secretary of Transportation to carry out a program to improve commercial motor vehicle safety in the vicinity of the borders between the United States and Canada and the United States and Mexico.

Authorizes the expenditure of funds for: (1) the employment by the Department of Transportation or a border State of additional personnel to enforce commercial motor vehicle safety laws; (2) the training of personnel to enforce such laws; (3) the development of databases and communication systems to improve commercial motor vehicle safety; and (4) education and outreach initiatives.

Sets forth provisions regarding: (1) criteria for selecting activities and projects for funding; (2) the Federal share of funding for such activities; and (3) maintenance of effort requirements with respect to State expenditures for the employment of such personnel. Authorizes appropriations.