My ten mile round trip commute can be either 90 percent on a busy shared use path or 100 percent on city streets with some bike lanes. This is an inner suburb of DC. I've been doing this year round in all weather on a daily basis for six years. For the past four years I have extended this to a 25 mile round trip commute, 95 percent on shared use trail. The shorter route is rolling hills, the longer route is a slight downhill going to work and a slight uphill coming home.