Possible Clues:

• The Queen spoken to, having squashed rat that's driven over
• Bill, grabbed by impertinent girl, leaving coat on road?
• Waterproof coat found by a mother – something on road?
• Broken stone for paving
• Road surface of crushed stone mixed with tar
• It’s worn by drivers about to stop lady
• Material for road surfacing
• Broken stone used in paving
• Pavement material
• Surface of river reflected man in garden