Willys made a variety of Hi-rail vehicles - trucks and wagons - for use on both highway and railroad tracks. These were US manufactured and titled by Fairmont and referred to as Hi-rail vehicles. Hy-rail is short for Highway-railroad.
Fairmont Railway Motors Inc, located in Fairmont, MN, developed road-rail technology in the 1940s to improve flexibility of vehicle use for railroad maintenance. Fairmont was bought by Harsco in the late 1980s. Hy-rail is still a trademark of Harsco Track Technologies and they still sell conversion kits called Hy-Rail Guide Wheel Attachments.
Hy-rail Production Notes:
A Pictorial History of Willys Hy-rail Vehicles
A special THANKS to Paul Barry for sharing these pictures and production notes