During a solo instructional glider flight, the student pilot released from the tow airplane at a planned altitude of 4,250 feet mean sea level (msl). Upon the release, the pilot was not able to locate any up-currents, and the sink rates the glider encountered varied between 200 to 600 feet per minute. The pilot stated that his plan was to try and gain altitude, cross a ridge, and drop back down into the valley and glide back to the airport. However, there was insufficient lift to clear the ridge safely, so he selected two open fields for a possible off-field landing. The pilot stated that on final approach to the field, he observed some signs between the glider’s current position and the intended landing site that he had not seen during his fly-by inspection. He maneuvered around the obstructions and decided to land on a road, which was his second landing site. The glider landed on the road, and the right wing collided with a previously unseen mailbox post, which caused substantial damage to the wing. The glider spun in a clockwise direction and hit trash cans before coming to rest in a shallow ditch.