Training as a commuter... for what goals? Racing? Weekend Warrior? Fitness?

A few things you might do.

• Bump it up to 5 days a week if possible.
• Are you using Strava? Choose a couple of segments to hammer, or perhaps a few hills to conquer. If no appropriate segments have been defined, then define your own. BE SAFE
• Are there hard and easy routes? Don't shy away from the more challenging rides?
• Do you have time to add a few extra loops to your ride? Perhaps 9 miles in the AM and 20 miles in the PM?
• I'm a slow rider, but I've made a goal of hitting 20 miles at 20 MPH. I'm halfway there with about 10 miles at 20 MPH (with small hills). Nonetheless, choose some goals that will be a challenge for you, and work on them. Maybe a little at a time. For example, hold 20 MPH as long as you can. 1 mile. A couple of miles.