The macadam road, with a clean crushed aggregate wearing course, is mechanically interlocked by rolling and linked together with a mixture of filler material (sand or clay) and water that is deposited on a prepared base course. The abbreviation is "WBM Road." The first macadamized roads were built in Pennsylvania in 1815. Macadamization was originally invented by John McAdam (1756-1836), an Irish civil engineer who spent most of his career working in Scotland. He is considered the father of modern highway engineering. John McAdam's invention involved replacing dirt roads with gravel ones to make them more durable. He also suggested using large stones as traffic markers so drivers would not have to stop constantly to check maps or guideposts. His ideas were very popular in Scotland at the time and many towns there started building macadamized roads. When they were done, these roads were found to be much easier to drive on than grassy or muddy paths. They were also much safer because of the lack of potholes and other obstacles that could cause accidents. In America, the first macadamized road was built by Benjamin Franklin Butler in 1815. It was a military road between Philadelphia and New York City for use by American soldiers returning from war. After this trial run, other governments began adopting the new technology for their own roads.