Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Human Factors
I was working the log while Local Control 1 was issuing a 'low approach only' instruction to Aircraft Y on short final. Aircraft X called from RWY 25R north side run-up area requesting right closed traffic; however; because the pilot over-keyed the Local Control Controller; the beginning of the transmission (call sign and position) was clipped. Local Control 1; realizing that his transmission may have been blocked; restated his instructions to Aircraft Y. Aircraft X then stated 'Right closed traffic RWY25R; Aircraft X'. I saw Aircraft X move forward; however; I did not recognize that he was passing the hold short lines. I did watch to make sure the aircraft came to a complete stop; which it did; still clear of the runway; just before Aircraft Y crossed the threshold. While there was no time to have sent Aircraft Y around; I should have recognized that Aircraft X was passing the hold short lines as I watched it move forward. It wasn't until Aircraft X asked for verification that he was cleared for [Runway] 25R and other controllers stated that he had crossed the lines that I realized this was the case.Because of the low height of our Tower; it's difficult for us to see our hold short lines. The lines are also closer to the runway on the north side than they are on the south side. I've been at this facility for several years now however; so I'm used to this being an issue and have caught mistakes like this before. Traffic volume was very heavy and there was some complexity due to the fact that we were split; training on Local Control 2 and a relief briefing had just occurred on Ground Control. I may have been trying to multi-task too much; dividing my attention between Local Control 1; Local Control 2 and Ground Control; rather than giving each of them all my attention at different times. I will be more careful in the future to give all my attention to one position at a time.
Livermore Tower Controller reported a runway incursion.