Narrative:

I was working local control. We had recently changed from south flow to north. I controlled one departure runway and one arrival runway. Due to some weather build ups in the airspace we were instructed to depart aircraft using radar vectors instead of RNAV departures. In this configuration; most aircraft are issued a 010 heading and an altitude of 10;000 ft. This can add a lot of phraseology to every transmission and you must pay close attention as read-backs are often incorrect due to the sequence of numbers in the heading and the altitude.aircraft X landed and indicated they were parking on the west side of the airport when questioned. I issued instructions for the aircraft to taxi and to hold short of the left runway. The aircraft gave a good read-back and indicated this on my scratch pad as per our SOP. I cleared aircraft Y for takeoff on the left runway and then instructed aircraft X to line up and wait on the same runway. I believe I then cleared an aircraft to land and ensured the arrival runway was clean. During my scan; I saw aircraft X moving pretty quickly and starting to cross the runway. I immediately checked for the progress of departing aircraft Y but they were too fast and committed to becoming airborne. I thought the best option would be to expedite the crossing of aircraft X to prevent overflight. The aircraft complied. I told the pilot they crossed without authorization and issued the brasher warning. He came back quite confident that I told him to cross; which really threw me off and made me question what just happened. I was spending more time than I should've needed in watching my final as aircraft were too close on final and compressing. The traffic management coordinator called down to the approach control on at least one occasion to ask them to provide us with the minimum 5 miles in trail on that runway due to construction. We were seeing 3.5 to 4 miles pretty regularly which then requires a lot of extra prompting to ensure the aircraft can clear the runway in time; taking your focus off of other areas.with the already increased phraseology in using radar vectors; multiple crossings; land and hold short instructions; etc. And having to work the aircraft on final due to compression and improper spacing; [it] made the situation a bit more complicated and an incursion easy to miss. Assist was not open at the time; but when it is; their focus is typically on the same area as yours and they are helping to ensuring proper read-backs. I don't believe assist would have prevented this specific situation.the pilot gave a good read-back and then simply just didn't do what they said they would. I think proper spacing on final may have helped allow me to focus somewhere else during my scan; but [with how] fast aircraft X was moving I still don't know if I would have caught the illegal crossing in time. I don't know if pilots use memory aids in the flight deck for crossing situations; but that could be potentially helpful. It would also be helpful for pilots to know when they are given a phone number; the frequency isn't the place to make their case. It's just notifying them of a potential deviation and nothing has been determined yet. It becomes more difficult to reset and refocus after a situation like that when the pilot wants to defend themselves on frequency. It's a stressful time for everyone involved.

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Original NASA ASRS Text

Title: Tower Local Controller reported not observing in a timely manner that an aircraft taxied across a runway that another aircraft was taking off from.

Narrative: I was working Local Control. We had recently changed from south flow to north. I controlled one departure runway and one arrival runway. Due to some weather build ups in the airspace we were instructed to depart aircraft using radar vectors instead of RNAV departures. In this configuration; most aircraft are issued a 010 heading and an altitude of 10;000 ft. This can add a lot of phraseology to every transmission and you must pay close attention as read-backs are often incorrect due to the sequence of numbers in the heading and the altitude.Aircraft X landed and indicated they were parking on the west side of the airport when questioned. I issued instructions for the aircraft to taxi and to hold short of the left runway. The aircraft gave a good read-back and indicated this on my scratch pad as per our SOP. I cleared Aircraft Y for takeoff on the left runway and then instructed Aircraft X to line up and wait on the same runway. I believe I then cleared an aircraft to land and ensured the arrival runway was clean. During my scan; I saw Aircraft X moving pretty quickly and starting to cross the runway. I immediately checked for the progress of departing Aircraft Y but they were too fast and committed to becoming airborne. I thought the best option would be to expedite the crossing of Aircraft X to prevent overflight. The aircraft complied. I told the pilot they crossed without authorization and issued the brasher warning. He came back quite confident that I told him to cross; which really threw me off and made me question what just happened. I was spending more time than I should've needed in watching my final as aircraft were too close on final and compressing. The Traffic Management Coordinator called down to the Approach Control on at least one occasion to ask them to provide us with the minimum 5 miles in trail on that runway due to construction. We were seeing 3.5 to 4 miles pretty regularly which then requires a lot of extra prompting to ensure the aircraft can clear the runway in time; taking your focus off of other areas.With the already increased phraseology in using radar vectors; multiple crossings; land and hold short instructions; etc. and having to work the aircraft on final due to compression and improper spacing; [it] made the situation a bit more complicated and an incursion easy to miss. Assist was not open at the time; but when it is; their focus is typically on the same area as yours and they are helping to ensuring proper read-backs. I don't believe Assist would have prevented this specific situation.The pilot gave a good read-back and then simply just didn't do what they said they would. I think proper spacing on final may have helped allow me to focus somewhere else during my scan; but [with how] fast Aircraft X was moving I still don't know if I would have caught the illegal crossing in time. I don't know if pilots use memory aids in the flight deck for crossing situations; but that could be potentially helpful. It would also be helpful for pilots to know when they are given a phone number; the frequency isn't the place to make their case. It's just notifying them of a potential deviation and nothing has been determined yet. It becomes more difficult to reset and refocus after a situation like that when the pilot wants to defend themselves on frequency. It's a stressful time for everyone involved.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.