On the highway, with more congested (but not traffic jam
) hours with lots of cars, a lane shield is the car hovering next to you while you are trying to get into their lane. Sometimes this is even intentional by the driver because they feel you may be trying to cut them off. Usually they will tailgate the vehicle in front of them so that you have to brake hard or speed up infront of them both to get into their lane.
I missed my exit because of that stupid lane shield in the pick up truck.