Transportation in Philadelphia involves the various modes of transport within the city and its required infrastructure. In addition to facilitating intracity travel, Philadelphia's transportation system connects Philadelphia to towns of its metropolitan area and surrounding areas within the Northeast megalopolis. The city is crossed by the Delaware Expressway (Interstate 95 or I-95) and the Schuylkill Expressway (I-76), which are the principal thoroughfares for intercity traffic. The Vine Street Expressway (I-676) travels between I-76 and I-95 in Center City Philadelphia, and the Roosevelt Boulevard (U.S. Route 1) carries crosstown traffic in northern Philadelphia. Philadelphia's public transit system is mainly operated by the Southeast Pennsylvania Transportation Authority (SEPTA), which maintains an extensive system utilizing buses, rapid transit, commuter rail, trolleys, and the Philadelphia trackless trolley (trolleybus) system. The main rail station of Philadelphia is 30th Street Station, which has access to 13 SEPTA Regional Rail routes and 11 Amtrak intercity rail routes. Philadelphia International Airport, the primary airport of Philadelphia, is a hub for domestic and international aviation. Roads Streets Grid plan The streets of Philadelphia mainly follow a grid plan, one of the first such lay-outs used in a North American city. The grid plan originated in 1682, when William Penn founded Philadelphia and appointed Thomas Holme as his surveyor. Using , Penn planned a system of organized streets to facilitate future growth. Since Penn survived the Great Fire of London and wanted to avoid similar catastrophes, he laid out streets wider than usual. Penn planned the city to stretch between the Delaware and Schuylkill Rivers, and his grid plan of present-day Center City followed a 22-by-8-block pattern. The plan included a large square in the center of the town (present day location of Philadelphia City Hall), and four public squares near each corner of the city. Since the initial grid covered only the area of present-day Center City, other settlements such as Kensington developed using different grids. The grid system was gradually extended to other regions of present-day Philadelphia, although several roads predating a grid system still exist. Certain neighborhoods of Philadelphia, such as those in the Far Northeast, do not use grid systems. Names When the street grid was designed by Penn, he named the east-west streets after trees (although four have since been renamed), and assigned the north-south streets numbers, starting with Front Street by the Delaware River. Market Street, running east-west, and Broad Street, running north-south, are