Trucks and cars share the same type of infrastructure, i.e. highways. The presence of trucks on highways, in addition to negative environmental impacts, may result in the reduction of the highway's capacity. In recent years, platooning trucks has been considered as a potential approach to mitigate such negative impacts. In spite of this, platooning trucks is not deployed in a large scale. This paper, develops a traffic evaluation building block for studying the effect of truck platoons on the system-wide traffic operations on highways using variational theory. The results of some representative scenarios show that the effectiveness of platooning strategies highly depends on the initial traffic state, as well as the characteristics of the platoon, i.e. its speed and length. Then, it proposes an event-based Decision Support System for realtime platooning of trucks on highways, based on the traffic evaluation building block.