As steam came to a close in America there were still a few wooden cars running in backwater railroads.
All wood passenger car ‘Royal Blue’ B&O RR, 1890 (Wikipedia)
Most of those had been replaced by steel cars of much greater strength. By 1960 most of the old steel cars had been replaced by modern ‘streamliner’ type cars.
Streamlined Pioneer Zephyr, 1934 now at Museum of Science & Industry, Chicago (Wikipedia)
Several train wrecks had shown that high-speed crashes were devastating as the new cars were of light construction and not very crashworthy. On Wikipedia you will find a list of train accidents across the globe by decade. This lead to regulations that governed car and locomotive construction. In Europe, cars and locomotives became lighter to allow higher speeds. Often, aluminum and composite construction reduced weight and added speed by streamlining the shape. New wheel and suspension arrangements along with roadbed improvements increased speed even more. It soon became obvious that these new structures were not very passenger friendly in the event of a derailment or collision. The ICE train derailment at Eschede, Germany is an example of the problem with the newer design and construction. This crash was at 125 mph and the remains of the coaches are reminiscent of train wrecks of 100 years ago. The lightweight coaches telescoped and were splintered, killing more than 100 and injuring about the same. The derailment was due to a wheel fracture that was undetected. The wheel was a composite design, a type of wheel that was outlawed in America in the 1930s.
There is a huge difference in how lightweight cars respond to an accident at high speed when compared to current American car construction. American passenger cars have a collision post at the ends that prevent telescoping at the expense of extra weight. Amtrak bought some passenger cars from Bombardier for use on short and medium length routes. Once in the US, they needed conversion to AAR standards as corner steps and handrails were not installed, as in the regulations. The cars were aluminum, and soon they became damaged in car/train collisions due to the ‘soft’ skin. They were very pretty when new, but soon were scared and hard to repair. Additionally, they did not do well in train crashes.
Amtrak Superliner Dining car (Wikipedia)
Other new Amtrak equipment, the ‘Superliner’ cars, were manufactured with German suspension systems that incorporated leaf springs that doubled as wheel alignment bars. The system worked well in Europe, but the constant pounding from crossing the rail joints on North American railroads led to frequent failure due to cracking that resulted from the vibration.
Building rail equipment to American safety standards adds lots of weight and cost. It does result in a safer product and saves lives.