Transportation in New Jersey utilizes a combination of road, rail, air, and water modes. New Jersey is situated between Philadelphia and New York City, two major metropolitan centers of the Boston-Washington megalopolis, making it a regional corridor for transportation. As a result, New Jersey's freeways carry high volumes of interstate traffic and products. The main thoroughfare for long distance travel is the New Jersey Turnpike, the nation's fifth-busiest toll road. The Garden State Parkway connects the state's densely populated north to its southern shore region. New Jersey has the 4th smallest area of U.S. states, but its population density of 1,196 persons per sq. mi (462 persons per km2) causes congestion to be a major issue for motorists.