Scott Seyfarth (Ph.D. 2016) and Marc Garellek published an article in LabPhon entitled “Physical and phonological causes of coda /t/ glottalization in the mainstream American English of central Ohio.”
In this paper, Scott and Marc claim that voiceless stops in American English involve glottal constriction to produce voicelessness in coda position. The distribution of glottalized coda /t/ in the Buckeye Corpus can be explained by phonetic conditions which either favor reduction of the oral closure, or else reinforce the irregular voicing associated with the glottal constriction gesture. However, they find evidence that glottalization is also phonologically planned, especially before sonorants.
Seyfarth, S., & Garellek, M. (2020). Physical and phonological causes of coda /t/ glottalization in the mainstream American English of central Ohio. Laboratory Phonology: Journal of the Association for Laboratory Phonology, 11(1), 24. DOI: http://doi.org/10.5334/labphon.213