List of Interstate Highways
There are 70 primary Interstate Highways in the Interstate Highway System, a network of controlled-access freeways in the United States. They are assigned one- or two-digit route numbers, whereas their associated "auxiliary" Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south-north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west-east, with lower numbers in the south and higher numbers in the north. Highways whose route numbers are divisible by "5" usually represent major coast-to-coast or border-to-border routes (ex. I-10 travels from Santa Monica, California, to Jacksonville, Florida, traveling from the Pacific to Atlantic oceans). Additionally, auxiliary highways have their numbering system where a different number prefixes the number of its parent highway.
Transportation in Dallas
The city of Dallas is at the confluence of a large number of major interstate highways—Interstates 20, 30, 35E, and 45 all run through the city. The city's freeway system, as it has no major geographical inhibitors surrounding it, is set up in the popular hub-and-spoke system, much like a wagon wheel. The center of the system is the downtown freeway loop, made up of Interstate 30 on the south, Interstate 35E on the west, Spur 366 on the north, and Interstate 345 on the east. (Interstate 345 is a short spur of Interstate 45 that connects Interstate 45 with US 75.) The next major freeway loop is the Interstate 635/20 Lyndon B. Johnson loop, and the outermost is the tolled President George Bush Turnpike. Inside these freeway loops are other partially limited-access and parkway-style loops including Loop 12 and Belt Line Road. Another beltway around the city is planned upwards of from downtown in Collin County. Radiating out of downtown as the spokes of the system are Interstates 30, 35E, and 45, US 75, US 175, Spur 366, the tolled Dallas North Tollway, and further out SH 114, US 80 and US 67. Other major highways within the city that do not serve primarily as spokes include SH 183 and Spur 408.