sentences: a runway is a kind of pathway for airplanes & as the number of pathways increases , the traffic congestion in that area usually decreases ->  as the number of runways increases, the traffic congestion in that area usually decreases  as the number of runways increases, the traffic congestion in that area usually decreases & airports have runways for airplanes -> as the number of runways increases, the traffic congestion at the airport usually decreases