Recent advances in cooperative driving hold the potential to significantly improve safety, comfort and efficiency on our roads. An application of particular interest is platooning of trucks, where it has been shown that keeping a minimum inter-vehicle distance results in considerably reduced fuel consumption. This, however, puts high requirements on timeliness and reliability of the underlying exchange of control messages between platoon members. The European profile of IEEE 802.11p, recently adopted by ETSI, defines two message types to this end, periodic beacons for basic cooperative awareness (CAM) and event-triggered decentralized environmental notification messages (DENM), both of which will use one common control channel. IEEE 802.11p employs a random medium access protocol, which may experience excessive delays during high network loads. To mitigate these effects, ETSI standardizes a decentralized congestion control algorithm to, e.g., lower the CAM update frequency during high loads. However, this may prevent proper functionality of a platooning application. In this paper we propose a solution that instead uses a dedicated service channel for platooning applications and compare its performance to standard-compliant IEEE 802.11p inter-platoon communication on the control channel. Service channels typically have less strict requirements on send rates, data traffic types and medium access methods. Our service channel solution combines a random access phase for DENM with a centralized, scheduled access phase for CAM. Using a service channel enables us to guarantee timely channel access for all CAM packets before a specified deadline while still being able to provide a reasonable DENM dissemination delay.