Originally Posted by OneIsAllYouNeed

I've been a 20+ mph commuter at times, but also a 17mph commuter and 15mph commuter. Almost all of my bike commuting from 2006 to present has been on a fixed gear with 28mm tires, like the OP. First I used a Redline 925 with drop bars, 42x15 gearing, typically a Chrome Citizen messenger bag. Currently I have a Voodoo Agwe with 45x15 gearing, TT bars, and behind-the-seat bag that's pretty aerodynamic. There have been a whole bunch of other setups in the mix - geared bikes, studded tires, panniers, etc.

I commuted from Billerica to Cambridge daily for 9 months back in 2011. The route mostly included the Middlesex Turnpike and Minuteman bike path, which has an infuriating number of stop signs. Other parts of my route were chosen to minimize traffic lights. I'd estimate I averaged 17mph most of the time. I think I may have topped out at 19mph average once or twice on that route. It was during the dark days before Strava, but after I kept a ride log notebook .

Since 2011, I've had rural/subuarban commutes in the NH seacoast area. The routes generally avoid traffic lights and stop signs to the greatest extent possible -- approximately 5 traffic lights in 19 miles. About 600ft elevation gain in that distance, which is fairly flat. The roads are a mix of town-maintained paved back roads with a couple of busier state roads. I've always lived northwest of my office. In the winter time, the prevailing winds are such that it's really hard to average 15mph at 200W on a road bike. I refined my aero commuter bike setup during those torturous winter commutes. Come summer time, those same ~200W were good for 20mph average door-to-door. There were a few weeks during summer time with a 20+mph average. Now most of my bike commutes on a geared cross bike with a toddler seat, I'm back down to 18-19mph average.

So you want a faster bike commute? This is the order I'd recommend.
1. Avoid stopping as much as possible.
2. Pedal steadily.
3. Reduce your transition times (time to park bike, get your gear on/off the bike)
4. Train to get faster.
5. Get more aero.
6. Get tires that aren't slow.