This morning commenced fixed gear experiment number 2. It went OK this time. The bike is an old steel road bike conversion. Gears are 39x15 (70 gear inches). Cranks are 165mm long. Pedals have Power Grips (straps).
There are a couple of factors which caused this second experiment to be more successful than the first. One is bike fit. The second is that I used the brakes to slow myself on the descents. In the first experiment, I tried to regulate my speed with my legs. No sore knees this time.
The only issue I had was trying to get my feet in the Power Grips when starting from a dead stop. I hit all the lights red too. So I got to fiddle around trying to get my feet in the straps while pedalling several times. I think the answer is to learn how to track stand at the stoplights.