WASHINGTON — The normally weekday-only Virginia Railway Express is set to offer special Sunday service on Aug. 23 for fans attending an auto racing around Washington’s National Mall. But VRE says it will also be significant as the agency explores the possibility of regular weekend service, currently expected to begin following the completion of major infrastructure projects including the second Long Bridge over the Potomac River. “VRE is thrilled to provide weekend service to our community and visitors on August 23,” VRE CEO Katie Choe said in a press release.