For years I rode fixed 48x15 w/a 550 foot drop into work w/a 550 ft climb homeward. Most of the vert was on one hill. To climb it I just did shallow switchbacks. Then as I got stronger I extended the vertical until I was only doing 4 turns. This was very rural and at night as I worked 2nd shift. So no traffic worries.

My r/t daily commute was 42 miles. For 6 years my mileage averaged 12,000+. It seems crazy now, but it seemed normal at the time. So, there really are no rules. Find a gearing that works best for you on your commuting terrain. In retrospect I should have used ss to save on my knees, but I just loved riding fixed. lol