Heavy vehicles and cars have different manoeuvrability and acceleration characteristics. Heavy vehicles thus influence a traffic stream in a different manner to passenger vehicles and cause different levels of traffic instability. The increasing number and proportion of heavy vehicles on the road may result in quite different traffic flow characteristics. Over the last half a century many studies have modelled car drivers’ car following behaviour. However, the existence of heavy vehicles in the traffic stream has not received the same attention. This paper investigates the different car following behaviour of drivers in heterogeneous traffic conditions. It explicitly considers the existence of heavy vehicles in general traffic and their interaction with other vehicles. Four types of passenger car and heavy vehicle combinations were considered. These were car-car, car-heavy vehicle, heavy vehicle-car, and heavy vehicle-heavy vehicle. A real world data set from a freeway in USA was used to show the different car following behaviour of drivers for each combination. This study analyses the space and time headways, driver’s reaction times and vehicle accelerations. It also introduces different Weidemann car following thresholds for each car following combination. It was found that the presence of heavy vehicles causes larger space and time headways, longer reaction time and more robust car following behaviour. It also shows that the car following threshold’s are different for each combination. The findings of this paper indicate that further research is required to develop a car following model that incorporates these behavioural differences.