Regulatory approval for new equipment required?

[SouthernRailway]

Given all of the government regulations about what type of brakes, horns, safety equipment, etc. a locomotive, piece of rolling stock or other equipment must have:

When a manufacturer has a new product, does the manufacturer typically obtain government certification that the product meets all regulatory requirements? Do railroads require government certification that a product meets all government requirements? Or does a manufacturer just do its best to make sure that the product meets all government requirement, but without seeking an official government "seal of approval"?

Does the AAR give a "seal of approval" to new equipment, evidencing that it meets all government requirements?

Thanks.

[Cowford]

In the case of tank cars, each design must be approved by the AAR (which would incorporate all FRA requirements). Once built, the manufacturer must submit a "certificate of construction" to the AAR indicating the car or car series was built in conformance with the approved design. This is actually stated in FRA regs with the AAR acting as FRA's proxy.