Highway hierarchies speed up routing through a road-network graph by assigning roads levels, such as residential road, national road, and highway. The aim is to avoid exploring millions of nodes when an interactive navigation app needs a route. section 4.3.4
Road levels can be supplemented with data such as designated speed and number of turns. A modified search, using bidirectional Dijkstra’s or A*, considers both distance to the destination and the type of road it might explore next. Far from the destination, it favors highways; closer in, it also considers national roads and then residential streets. section 4.3.4
New York to Miami
A long-distance drive starts on local roads, joins a highway for the middle of the trip, and returns to local roads near Miami. The hierarchy focuses the long middle stretch on major roads rather than searching every nearby street. section 4.3.4
