John McAdams was a scottish engineer who modernized the way we built roads.
He is important to transportation because of the changes he made to roads. At the time, roads were dirt paths, and were susceptible to damage and wear, breaking down fast after much use.
He changed the roads by making sure the roadbeds were raised to make sure there was adequate drainage. The roadbeds were then laid with broken stones in symmetrical patterns, and covered with small stones to make a hard surface. McAdam discovered that the best stone or gravel for road surfacing had to be broken or crushed, and then graded to a constant size of chippings.
This revolutionized roads, and helped a lot in regards to transportation, making it easier, faster, and more comfortable.