Final answer:
Cars manufactured after 1968 were required to have seat belts, and following the Clean Air Act of 1970, catalytic converters were also mandated to meet new pollution standards, leading to reduced emissions and cleaner air.
Step-by-step explanation:
The equipment required on all cars manufactured in 1968 and after, in addition to mufflers, were seat belts. In the years that followed, specifically after the Clean Air Act of 1970, which was signed by President Nixon, catalytic converters became mandatory for automakers to include on every new car. These catalytic converters are devices that use catalysts to change the chemical properties of exhaust, helping to reduce vehicle emissions by 90 percent.
The inclusion of catalytic converters and the switch to lead-free gasoline led to an increase in the price of new automobiles, which was a subject of displeasure among muscle-car enthusiasts. However, this addition played a significant role in reducing the smog that had been a problem in American cities since the 1950s.