In Taiwan, more than 400,000 new autos are sold every year. Thus distributing these new autos from manufacturing centers to dealers in an efficient manner is an important issue. In real world, the auto carrier uses tractors and trailers to distribute new autos to dealers. The distribution planning process includes three stages: first, planning on the new auto distribution route; next, planning on the loading of new autos into trailers; finally, planning on the tractors' route. If the new autos are unable to be completely loaded into the trailer based on route planning of the first stage, the auto carrier will need to reroute to improve the loading of autos. The process of rerouting will increase the operation time and cost. Therefore, this paper integrates the loading factors into the route planning process and this problem is called the new auto distribution routing problem with same trailer loading constraints. An integer programming model was constructed for solving this problem. Besides, since using the proposed model to solve large-scale problems can be difficult, a heuristic algorithm was developed. The results by applying the model and heuristic algorithm to solve the test problems are conforming to all problem factors. Therefore, the result of this paper can be referenced for future research and by autocarriers.