Date: 201510
Local time of day: 0001-0600
Location: IAH.Tower, TX
Light: Dawn
Aircraft: Widebody; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower IAH
Second aircraft: Widebody; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach; General Flight Cancelled / Delayed
Contributing factors: Aircraft; ATC Equipment / Nav Facility / Buildings; Airport; Environment - Non Weather Related; Human Factors; Staffing
Primary problem: Human Factors

Narrative: Aircraft X landed and rolled long. I made him aware that traffic on final behind him. He rolled to the end. It then became a squeaker. I had several tugs and people calling me on ground control and another controller trying to open to take the local control position. I was keeping an eye on the runway for the Aircraft X to clear. It was going to be tight. [Another controller observing] had said they didn't think it was going [to] work; but it looked like it still may. Like I said I had tugs calling for re-position and was getting other calls on the combined frequencies. I let it ride as long as I could because I know these crews landing at that time of the morning are exhausted and just want to get on the ground and go home.  I saw that Aircraft X was across the line; but I couldn't make out if he was completely clear (tail) of the runway and nothing was impeding him. So I sent Aircraft Y around. I probably could have done it a mile before; but like I said; I really hate sending these early morning arrivals around. I watched the ASDE-X replay and couldn't tell there either if the Aircraft X was clear or not. I guess Quality Assurance will determine that. It was close. In the end I did the safe thing (subjective; thought the pilots were probably fully awake now) and sent him around. The ASDE-X never sounded.I would recommend that [airline company] wait 10-15 minutes later to start doing aircraft re-positions. Controller position relief is happening so we are conducting multiple relief briefings and we have a few arrivals opposite direction from the west coast and overseas at that time of day. 10-15 minutes later all is calm for the next half hour to 45 minutes. If you are busy on another frequency the tugs and especially the mechanics taxiing aircraft will continue to call. Not their fault; they aren't pilots or controllers. The company just needs to make it a policy not to move re-position aircraft until [15 minutes later]. Simply my opinion.Like I said; I could have sent the second aircraft around sooner but I hate to do that especially to these guys who have been up all night.




Synopsis: Landing aircraft was possibly not going to completely clear the runway onto the taxiway; so the Controller issued the subsequent arrival a go-around clearance. Reporter was not sure if required runway separation existed or not.