outer ring road; orbital road
A road that encircles the outer part of a city or metropolitan area, often part of an expressway network.
The Tokyo Outer Ring Road is an important arterial road connecting areas away from the city center.
環状道路 is a general term for any ring road, while 外郭環状道路 specifically refers to an outer ring road encircling the periphery of a city.
Compound of 外郭 (がいかく, 'outer enclosure') + 環状 (かんじょう, 'ring-shaped') + 道路 (どうろ, 'road').