The Red Line serves the Airport MAX extension, which is long. This extension begins just south of Gateway Transit Center where it branches from the Eastside MAX segment, makes a 180-degree loop, and heads north along the east side of Interstate 205. Near Rocky Butte, it enters a tunnel beneath the northbound lanes of the freeway and emerges along the median. Just south of the Columbia Slough, the line bridges over southbound I-205 towards Cascade Station and proceeds northwest along the south side of Northeast Cascade Parkway. It follows this road then crosses it just before Mount Hood Avenue station. The line proceeds northwest along the south side of Northeast Airport Way until it reaches its terminus at Portland International Airport station. Beyond the Airport MAX, Red Line service travels along parts of the Westside and Eastside MAX segments, running alongside the Blue Line from Beaverton Transit Center to Gateway Transit Center and the Green Line from Rose Quarter Transit Center to Gateway Transit Center.