transcontinental route of I-80. Just as I-5 leaves Sacramento, SR 99 splits off and continues north while I-5 turns due west past Sacramento International Airport and crosses the Sacramento River into Yolo County. In Woodland, the SR 113 freeway merges with I-5 before exiting to the north. The Interstate heads northwest again toward Dunnigan, where it converges with I-505. I-5 skirts north along the western edge of the Sacramento Valley, bypassing the larger cities of the region, including Yuba City, Oroville and Chico, before reaching Red Bluff. From Dunnigan, I-5 enters Colusa County, passing through the city of Williams and intersecting SR 20. In Glenn County, I-5 intersects SR 162 in Willows and SR 32 in Orland. I-5 then crosses into Tehama County, passing through Corning before entering Red Bluff and intersecting SR 36, which connects to the northern end of SR 99. I-5 crosses the Sacramento River twice before entering Shasta County. Cascade Region I-5 then enters the Shasta Cascade region, intersecting SR 273 in Anderson before passing through Redding and intersecting SR 44 and SR 299. The freeway then continues through the city of Shasta Lake, intersecting SR 151, before crossing over Shasta Lake on the Pit River Bridge and climbing up to near the foot of Mount Shasta. Just north of the bridge over Shasta Lake, I-5 also boasts the second-largest median in California after I-8's In‑Ko‑Pah grade. In Siskiyou County, I-5 passes through Dunsmuir before intersecting SR 89 near Lake Siskiyou and entering the city of Mount Shasta. North of here, US 97 intersects I-5 in Weed, providing access to Klamath Falls, Oregon. The Interstate then continues to Yreka, intersecting SR 3 and SR 96 before crossing the Klamath River and reaching the Oregon border and the Siskiyou Summit. North of Redding, I-5 regularly gets snow at higher elevations from fall to spring. Caltrans sometimes requires vehicles to use snow tires, snow chains, or other traction devices in the mountains during and after snowstorms. Checkpoints are often set up to enforce chain restrictions on vehicles bound for icy or snowy areas. When chain restrictions are in effect, vehicles must have chains on the driving wheels, except 4WD vehicles with snow tires. Additionally, during the winter season, trucks are required to carry chains whether or not controls are in force. History Historical naming The portion of this highway from Los Angeles to San Diego was also co-signed