U.S. Dept. of Transportation investigators have opened a criminal inquiry into the use of federal funds for four downtown Seattle transportation projects. The USDOT, which is also auditing Seattle’s oversight of federal transportation grants, subpoenaed contract solicitations, awards, purchase orders, invoices, wire transfers and other documents related to the now-complete Mercer Street corridor reconstruction; management and operation of a limited-stop bus service; and the repeatedly delayed $286-million Center City Streetcar, which has doubled in cost since it was proposed in 2015.