Another glider pilot, who was thermal soaring about 1/2 mile from the accident site, observed the glider approach a field at low level. It circled the field in a wide radius turn, then moved about a quarter mile away. It then began to circle in a tight radius turn. The observing pilot looked away for about 30 seconds, and when he looked at the glider again, it was in a steep turn. The glider aligned with a two lane road then swerved abruptly left into a line of trees. A ground witness said that the glider appeared to attempt a landing in the field. The pilot overran the field and a go-around was made because of obstacles. The landing was aborted by pulling up. The glider nearly stalled and turned to land on the road. The left wing hit a road sign, veered left, and struck a tree. Paint transfer marks were found on the road which correlated with scrapes on the underside of the glider's fuselage. Examination of the glider, after the accident, did not reveal any flight control malfunctions.