It is a wrought-iron trestle 1,112 feet long and 137 feet high. On the sides of the ridges at either end of the viaduct, the number of tiers decreases to match the slopes.
Abutments are mortared ashlar masonry of brownstone blocks.
The embankment containing the viaduct is fine sand with a skin of packed cinders. The Air Line, which opened its complete route in 1873, was promoted by business interests from the Middletown area, which had been without direct rail service until that time. The ambitious plan never overcame the serious topographical and economic obstacles that had delayed railroad development in the area. Hoping to establish a reputation for reliability and technical superiority, the Air Line promoters built all their bridges of iron. Lyman Viaduct, the longer but otherwise similar Rapallo Viaduct, and the swing bridge over the Connecticut River at Middletown were the most expensive structures.