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The experiment examined the effects of Digital taxi (D-Taxi) clearances when either 40% or 75% of the departure aircraft were data link equipped and compared these conditions to voice-only operations. Sixteen Airport Traffic Control Tower controllers used the Tower Operations Digital Data System at the ground control and local control positions to control airport traffic with a 270- degree simulated out-the-window view. The controllers worked at each position in each experimental condition, provided ratings of subjective workload, and responded to questionnaires. D-Taxi clearances for departure aircraft reduced voice communication between pilots and the ground controller when 75% of the aircraft were data link equipped, without increasing workload or heads-down time. On average, the controllers took 1.28 s to construct and issue a D-Taxi clearance, and they preferred D-Taxi to voice because it reduced their communication duties and removed the potential for readback and hearback errors.