A Glasair II pilot reported that in turbulent flying conditions he was unable to accurately determine either wing tank's fuel quantity and mistakenly selected an empty tank. The engine quit and he made a safe off airport landing.

Narrative

I was enroute with a planned fuel stop. I had recently switched from my right fuel tank to my left fuel tank. The turbulence was such that my mechanical fuel gauges were bouncing and very hard to read and it appeared that I had less fuel in my left than my right so I switched back to the right tank. As I approached the planned fuel stop area at 4500 FT MSL; I attempted contact with Approach/Departure with no response so I tried the Tower also with no response although I was receiving clearly. I switched radios and repeated the process while maintaining 4500 FT MSL altitude and remaining outside the Class B airspace. While continuing to diagnose my communication problem the engine sputtered and died. I positioned for the best glide while switching to the left fuel tank; running through my checks for circuit breakers popped; etc.; and attempted to restart with no success. The engine sputtered once for a moment and died again. Although I could not transmit; I had been listening and looking for airborne traffic as well as on the nearby highway. It soon became apparent that I would not make the airport. There was no northbound traffic on the highway and only three vehicles southbound a considerable distance away; no high lines in my path and no road signs or obstructions; so I elected to land on the highway. The landing was without incident. I rolled out breaking normally and turned onto a culvert access to the highway so I would not block traffic. No damage or injuries were incurred. Corrective actions: 1) Upon inspection I found that my I had run my right fuel tank dry which caused the engine to die and that I did indeed have 14.1 gallons of fuel onboard (left tank). The following morning I was able to restart the engine with no problem. I had not properly managed my fuel. I have resolved to rely less on the mechanical gauges and to monitor my fuel burn; calculated with time; supported with detailed note keeping and timely switching of fuel tanks. 2) My communication problem was found to be a small cut in my headset wire. The headset has been replaced with a completely new headset. 3) Overall I intended to give more consideration to a layover in hopes of a less gusty atmosphere.