The objective of this paper is to estimate the PCE(Passenger Car Equivalents) of various vehicle types on expressway work zones. Headway samples of 5,359 vehicles were collected in 6 work zones in the Kyungbu Expressway between September and November of 1995. Average headways of 8 vehicle types based on the vehicle classification method of the Department of Construction and Transportation were calculated. A statistical test of effects of the types of the preceding vehicles were performed for the average headways between a vehicle type preceded by other vehicle types. The results show that the effects of the type of preceding vehicles are significant (exceeded 5% and 10% significance levels) and the PCEs of heavy vehicles on expressway work zones are higher than that of basic expressway section. Therefore, different adjustment factors should be applied for heavy vehicles in estimating saturation flow rates of expressway work zones. The study also derives an equation to determine PCEs of these vehicle types.