As a remedial measure for the congestion in rush hours in metropolitan areas, we developed a "Wide-Body Car" of which the floor area is increased up to 11% larger than that of traditional commuter trains without interfering with wayside ground facilities. The floor width of this car is slightly smaller than that of traditional cars, but the width for one passenger line is generated at the center of floor by devising a new car-body profile. The maximum width of this car exceeds the limit of rolling stock gauge by 50mm on each side. We measured the gap between car-body and structure clearance in running tests, and inspected it for safety. In addition, the running stability and the performance of elastic suspension system were checked by the lateral vibration tests on a vehicle plant.