What additional equipment is required on cars manufactured in 1968 and later beside mufflers?

Cars manufactured in 1968 and later are required to have an exhaust emission system in addition to standard mufflers. This requirement was established to control and reduce harmful emissions produced by vehicles, aligning with environmental regulations that were intensifying during that period to tackle air pollution. The exhaust emission system helps in reducing pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides through various components, such as catalytic converters and exhaust gas recirculation systems.

While noise reduction equipment might seem beneficial and could relate to vehicle operation, it does not have the same regulatory requirement as the exhaust emission systems that directly impact environmental emissions. Similarly, a second muffler and anti-lock brakes are not mandated for compliance with emissions regulations, which are specifically focused on controlling the environmental impact of vehicle exhaust. Thus, the requirement for an exhaust emission system reflects the movement toward stricter environmental standards in automotive manufacturing during this era.