OK, some info first.

My commute is a mere 5 miles, with a lot of traffic stops (17 stop signs, 8 traffic lights), but not so many that I can't speed along, if I feel like it.

At 5 miles, it is a nice jaunt, which I typically complete in 19 to 23 minutes, depending on what lights I hit.
I figure my short commute would be a good way to pack in a little more exercising by ramping up the intensity.
I could change my route to be more challenging, or bike longer, but that'd take extra time, and I barely get to work on time as it is

I am familiar with HIIT in terms of calisthetics, but not sure how to translate that into cycling.
I imagine this is mostly a wattage game, but not sure if I am better served increasing cadence, or increasing force?
I currently cycle around 80-90 RPM (best estimate, as I don't have a computer to measure it)

I am leaning towards higher cadence, as I feel higher force = mashing = spontaneous knee explosions

Given the amount of stop-and-go, would learning how to sprint be a good way to crank up intensity?