Jeep 2013 Grand Cherokee - Manual (Page 134)

The BSM system is designed not to issue an alert on
stationary objects such as guardrails, posts, walls, foliage,
berms, etc. However, occasionally the system may alert
on such objects. This is normal operation and your
vehicle does not require service. The BSM system will not alert you of objects that are
traveling in the opposite direction of the vehicle in
adjacent lanes.
Stationary Objects
Opposing Traffic
132 UNDERSTANDING THE FEATURES OF YOUR VEHICLE