partly because of the grid street patterns now absent in newer developments farther from the urban core, where suburban style arterial roads are much more common. As a result, the majority of cycling is recreational. In 2006, San Diego was rated the best city (with a population over 1 million) for cycling in the U.S. San Diego is served by the San Diego Trolley light rail system, by the SDMTS bus system, private jitneys in some neighborhoods, and by Coaster and Amtrak Pacific Surfliner commuter rail; northern San Diego county is also served by the Sprinter light rail line. The trolley primarily serves downtown and surrounding urban communities, Mission Valley, east county, and coastal south bay. A mid-coast extension of the Trolley operates from Old Town to University City and the University of California, San Diego along the I-5 Freeway since November 2021. The Amtrak and Coaster trains currently run along the coastline and connect San Diego with Los Angeles, Orange County, Riverside, San Bernardino, and Ventura via Metrolink and the Pacific Surfliner. There are two Amtrak stations in San Diego, in Old Town and the Santa Fe Depot downtown. San Diego transit information about public transportation and commuting is available on the Web and by dialing "511" from any phone in the area. The city has two major commercial airports within or near its city limits. Downtown San Diego International Airport (SAN), also known as Lindbergh Field, is the busiest single-runway airport in the United States. It served over 24 million passengers in 2018, and is dealing with larger numbers every year. It is located on San Diego Bay, from downtown, and maintains scheduled flights to the rest of the United States (including Hawaii), as well as to Canada, Germany, Mexico, Japan, and the United Kingdom. It is operated by an independent agency, the San Diego Regional Airport Authority. Tijuana International Airport has a terminal within the city limits in the Otay Mesa district connected to the rest of the airport in Tijuana, Mexico, via the Cross Border Xpress cross-border footbridge. It is the primary airport for flights to the rest of Mexico, and offers connections via Mexico City to the rest of Latin America. In addition, the city has two general-aviation airports, Montgomery Field (MYF) and Brown Field (SDM). Recent regional transportation projects have sought to mitigate congestion, including improvements to local freeways, expansion of San Diego Airport,