It was sloped at every drive-in I went to - so you'd see over the canteen/projection room.
Half the fun was queueing for burgers, chips (fries), and/or pizza, and coke between the two features. The other half was sneaking beer in. Then the other half was...... what was I talking about?
Lots of restaurants and cafes pouring their waste cooking oil down the sink instead of paying a collection service.