In 1938, several major innovations were introduced by the company to its school bus design, including its first steel-bodied school bus. While Perley Thomas streetcars had adopted steel construction in 1918, school bus design had slowly evolved from farm wagons, with wooden body construction continuing into the 1930s. Although not the first to construct an all-steel body, Thomas introduced one-piece roof bows, internal roll bars welded to each side of the floor/frame structure. While the design has been updated for added strength, the one-piece roof bow is in use in all school buses manufactured in North America today. In another innovation, Thomas introduced an outward-opening entry door, designed to aid egress in emergency evacuation situations.