Sensor technology plays a critical role in the operation of the Automated Highway System (AHS). The proposed concepts depend on a variety of sensors for positioning, lane- tracking, range and vehicle proximity. Since large substations of the AHS will be designed and evaluated in simulation before deployment, it is important that simulators make realistic sensor assumptions. Unfortunately, the current physical sensor models are inadequate for this task since they require detailed world state information that is unavailable in a simulated environment. In this paper, we present an open-ended, functional sensor hierarchy, incorporating geometric models and abstract noise characteristics, which can be used directly with current AHS tools. These models capture the aspects of sensing technology that are important to AHS concept design such as occlusion, and field of view restrictions, while ignoring physical-level details such as electromagnetic sensor reflections. Since the functional sensor models operate at the same level of granularity as the simulation platform, complete integration is assured. The hierarchy classifies sensors into functional groups. The models at a particular level incorporate characteristics that are common to all sensors in its subgroups. For example, range sensors have a parameter corresponding to a maximum effective range, while lane-trackers include information pertaining to lateral accuracy.