The latest developments in vehicle-to-infrastructure (V2I) and
vehicle-to-anything (V2X) technologies enable all the entities in the
transportation system to communicate and collaborate to optimize transportation
safety, mobility, and equity at the system level. On the other hand, the
community of researchers and developers is becoming aware of the critical role
of roadway infrastructure in realizing automated driving. In particular,
intelligent infrastructure systems, which leverage modern sensors, artificial
intelligence, and communication capabilities, can provide critical information
and control support to connected and/or automated vehicles to fulfill functions
that are infeasible for automated vehicles alone due to technical or cost
considerations. However, there is limited research on formulating and
standardizing the intelligence levels of road infrastructure to facilitate the
development, as the SAE automated driving levels have done for automated
vehicles. This article proposes a five-level intelligence definition for
intelligent roadway infrastructure, namely, connected and automated highway
(CAH). The CAH is a subsystem of the more extensive collaborative automated
driving system (CADS), along with the connected automated vehicle (CAV)
subsystem. Leveraging the intelligence definition of CAH, the intelligence
definition for the CADS is also defined. Examples of how the CAH at different
levels operates with the CAV in the CADS are also introduced to demonstrate the
dynamic allocation of various automated driving tasks between different entities
in the CADS.
