The Capital Region First Ring Expressway (Formerly as Seoul Ring Expressway) (Expressway No.100) (Korean: 수도권제1순환고속도로; RR: Sudogwon Je1sunhwan Gosokdoro) is an expressway, circular beltway or ring road around Seoul, South Korea. It connects satellite cities around Seoul, Ilsan, Namyangju, Hanam, Pyeongchon, Jungdong, Bundang, Pangyo, Sanbon and Gimpo. The expressway runs 127.6 km. Seoul Ring Expressway is currently under construction to widen the expressway between Anhyeon Junction to Seongnam which is expected to be finished in 2016.

Expressways in South Korea, officially called as National expressways, are owned by the government, and operated mostly by the Korea Expressway Corporation, and to a less extent by the private sector. They were originally numbered in order of construction. Since August 24, 2001, they have been numbered in a scheme somewhat similar to that of the Interstate Highway System in the United States; the icons of the South Korean Expressways are notably similar to those in the United States because they are shaped like U.S. Highway shields and colored like Interstate shields with red, white, and blue, the colors of the flag of South Korea.Arterial routes are designated by two-digit numbers, with north–south routes having odd numbers, and east–west routes having even numbers. Primary routes have 5 or 0 as their last digit, while secondary routes end in other digits. Branch routes have three-digit route numbers, where the first two digits match the route number of an arterial route. Belt lines have three-digit route numbers where the first digit matches the respective city's postal code. Route numbers in the range 70–99 are not used in South Korea; they are reserved for designations in the event of Korean reunification. The Gyeongbu Expressway kept its Route 1 designation, as it is South Korea's first and most important expressway.