When a railroad corporation has constructed a railroad across a public highway by passing over the traveled path thereof, the corporation shall keep in good and sufficient repair and rebuild when necessary, its bridges and abutments; however, construction of new bridges and abutments, and rebuilding and reconstruction of existing bridges and abutments, made necessary by reason of highway improvement incident to increased load, usage, or speed of motor vehicular traffic, shall be made by the railroad at State expense. (Added 1969, No. 76, § 4.)