Winter driving conditions have arrived on some Northstate mountain roads. Interstate Five was subject to chain restriction near the Oregon border Monday, leading to severe freeway backups. On Tuesday morning there are some restrictions in Lassen and Modoc Counties, as well as on Highway 36 in Tehama, Trinity and Humboldt. At least 2 big rigs jackknifed in icy conditions on Southbound I-5 at the Klamath River Bridge at around 6:30AM Tuesday morning, blocking the fast lane. A number of other spin outs have been reported on I-5 this Tuesday morning.