Abstract: A vehicle for traversing rough terrain, such as is commonly found in open mining operations and highway construction work. The vehicle is characterized by a movable frame structure. The frame includes a pair of elongated side members which are joined in a spaced apart relationship near the rear of the frame members by a first crossmember which is provided with a pivotal joint to permit the side members to rotate or pivot relative to each other. The front ends of the side members are connected by second and third crossmembers, each of which is pivotally connected at both ends to the side members to provide lateral restraint to the side members while the vehicle is traversing rough terrain. The second and third crossmembers are vertically displaced to prevent relative rotation of the side members about their longitudinal axes while permitting up and down movement of the forward ends of the side members as the side members rotate about the pivot point in the first crossmember.