Enhanced Taxiway Centerline Markings These markings indicate that the aircraft is approaching a runway. Prior to a runway holding position marking, the taxiway centerline will be "enhanced" to include a set of yellow dashed lines. Installed at more than 500 airports throughout the U.S., these dashed yellow markings extend 150 feet from the runway holding position on either side of taxiway centerlines. Ref. AIM Para. 2-3-4-b-2