I ride the Black Diamond section of the D&L Rail Trail system, and I start at the bottom and ride to the top. Very gentle grade. It is gravel, so you do have to pedal at least occasionally.

The trail is about 8.5 miles long and gravel. I pedaled about as many times on the way back as I did in each of the miles on the outbound portion. I usually soft pedal and ride at 14 mph or so on the way back, but I was with someone who really wanted to take it slow and enjoy the scenery, so I coasted most of it and probably averaged 8-10 mph.