One initial step in any new design is the selection of the applicable regulations (requirements). They will drive the design and ensure a product with the adequate level of safety.
Requirements are the result of years of experience and analysis of the products. For aircraft, as example, findings of an acident investigation may result in modification of requirements or addition of rules to ensure a safer product.
Airworthiness Requirements (or Certification Specifications) here are to be used as a reference only, as they are in a constant evolution and, in actual designs, the applicable requirements (usually the definition of the Amendment to be used) is frozen when the certification process starts.
Regulations available here:
FIA regulations can be downloaded direct from their site clicking the link above. The link redirects you to Formula 1 regulations. On the same page all other FIA categories are available.
NASCAR has also regulations for each racing series. They are released only to members and are not made available to the public.