On a technical note ... the MacAdam road (named for its engineer inventor) was composed (simpistically speaking) of layers of stone of diminishing size laid with a camber to make water run off. The impact of horses' hooves and iron wheel tyres crushed and compacted the top layer to make a fine-grained smooth water-repellant surface which was resistant to pot-holes; the more use it got, the better it became. The advent of wide rubber tyres, especially those on "high speed" motor-cars was bad news: the tyres sucked the finer particles from between the coarser stones, creating great clouds of choking dust, and causing the surface to break up. (That's why early motorists wore goggles and scarves.) Tarmacadam was the solution: the bitumen bound the stones together, giving a dust-free and more flexible surface to the road.

Steve