A vehicle may determine that it is stopped and detect a perimeter-modification event predefined as correlating to a changed vehicle perimeter. The vehicle may further, responsive to the perimeter-modification event, define an expanded vehicle perimeter, larger than a perimeter predefined as representing the vehicle in travel. The perimeter expansion may be done in accordance with a predefined modification associated with the detected perimeter modification event. The vehicle may additionally wirelessly share the expanded vehicle perimeter with at least one other vehicle.