A Legend Cub pilot landed on a paved road after encountering Unforecast fog with no airports in his vicinity.

Narrative

I was flying in VFR with 5 mile visibility or better when visibility started to decrease; but visibility was still 3 miles or better. Scud appeared under me which I had never experienced before and immediately I was in IMC and in a lot of trouble. Have calculated I was in IMC for at least 20-21 minutes with only a GPS HSI heading bug and small rate of turn indicator. Not instruments for flying IFR. In a protracted time (20 minutes) I decided I could no longer fly under the above circumstances. GPS showed no towns; airports; or towers in the area ahead. I let down at approximately 200 FT per minute until I broke out at approximately 200 FT AGL. I tried to fly to the nearest airport 18 miles distant; visibility and altitude made that impossible; so I landed on a blacktop two-lane highway; which turned out to be State Route 1. Human performance on my part was poor; although I had checked weather twice before flight and VFR was indicated; although obviously not present. However; I was the one who did not pick up changing conditions fast enough to react with a 180 degree turn when still in VFR conditions.