Highway traffic characteristics are shaped by the presence and dynamics of various vehicle classes, ranging from light vehicles to multi-class vehicles, sharing the roadway under diverse traffic conditions. Vehicle movement in heterogeneous traffic is affected by the interaction between different vehicle classes. Traffic density is typically used to determine the level of service provided to drivers. However, the concept of occupancy has been identified as a more suitable measure for describing traffic concentration when vehicles in a traffic stream exhibit significant variation in length and speed. This is because occupancy calculations take into account differences in vehicle lengths and speeds. Managing congestion in heterogeneous traffic situations characterized by mixed vehicle types and weak lane discipline remains a challenging task. This literature review aims to explore the effects of the fluctuating proportion of light vehicles to multi-class vehicles on highway speed, passenger car unit (PCU), capacity, and level of service (LOS). The paper first introduces the challenges arising in heterogeneous traffic and discusses the concept of area occupancy and its determination methods. Subsequently, the paper presents an estimation of traffic volume (PCU/h) using the area occupancy concept. The paper concludes by recommending the calculation of the correlation coefficient (R) to evaluate the variability of area occupancy and PCU per hour for vehicles.