I'm a delivery driver and I deliver food (frozen, chilled and ambient) to premises (pubs, burger vans, hotels, restaurants etc.) and sometimes the vans a packed full.
Some drivers have trays of bread placed on the passenger seat and when this happens more than one tray, often three or four trays.
When the need comes to brake urgently, there is a danger that the driver will be concerned that the trays could topple off the seat. He or she may not brake hard enough, and an accident may ensue.
However, I suspect a policeman may consider them an insecure load.