It might be worth it to check out the NerdFitness “how to become The Flash” superspeed routine here. It’s got some good science behind its sprinting ideals (and how it also helps create endurance for long distance running too). It also provides information on how to train your speed up correctly so you don’t end up injured or overexerted to the point of needing too much time to recover.

If you’re mostly sticking to the treadmill, I used to do a variation of the 60/120s on treadmills to get my 2-mile time down. I’d warm up for a few minutes then jog for 5 minutes, crank up the speed and sprint for one minute, bring it back down to a jog for 5, crank back up for another one minute sprint, etc. It took longer than 60/120s but it was safer to increase the 120s to five minutes on the treadmill. (If that’s something you try, make sure to find what’s most comfortable for you to prioritize safety, as reaching the controls to turn down the speed when you start getting worn out and sweaty can get slippery.)

Nowadays I mostly work out indoors in a home gym setup. Because of that, I rely a lot on a combination of plyometrics, cardio routines, and martial art drills to increase endurance, breath control, etc. Try a few things, take what you like and mix it up, maybe substitute one of your running sessions with plyometrics or shadow boxing, find what keeps you interested and keeps you pushing in a way that brings progress.