Paper 1. The AASHO road test system of nuclear density determination is described, with emphasis on the source of error that has been isolated and in some cases eliminated. Some of the important considerations in the design of nuclear surface gages are discussed, as well as calibration techniques, licensing, health precautions, and cost. Paper 2. The AASHO road test includes 16 single-lane, single-span highway test bridges located in the regular traffic lanes of loops C and D, the heaviest traffic loops. With steel I-beam bridges, four designed to the yield point stress of the steel and four to 27,000 psi, are included, along with four conventional and four prestressed concrete bridges. This report summarizes the construction of the bridges, completed in 1957.