This paper focuses on the design of controllers that ensure string stability in Heavy Commercial Road Vehicle (HCRV) platoons. While dealing with controller design for HCRVs, due to the sluggish nature of a pneumatic brake actuation system, the actuator dynamics has to be considered explicitly. Sliding Mode Control (SMC), which is a widely accepted control strategy for string stability has been considered and the effects of actuator dynamics during deceleration as well as acceleration phase were analysed. It was observed that, the actuation delays caused string instability using the designed SMC controller. In this context, a Variable Time Headway (VTH) based controller redesign that is capable of ensuring string stability despite actuation delays is presented. The efficacy of the presented VTH policy has been evaluated through simulations and it was observed that this policy could make the platoon string stable while accounting for real world actuator dynamics.