From Los Angeles and Orange counties: Interstate 10 east to the Running Springs Highway 30 exit in Redlands. Follow Highway 30 to Highway 330. #330 later turns into #18 and bring you all the way up the hill. Alternative route from I-10: I-10 East to Orange Street North in Redlands. Follow signs to Highway 38.
From San Diego County: Interstate 15 North to Interstate 10 East and follow above directions.
From Palm Springs: Interstate 10 West and follow above directions.
From the High Desert: Interstate 15 to Victorville. Exit at Bear Valley Road East to Lucerne Valley, Right on highway 18.
From Las Vegas: Interstate 15 South into Barstow. Take the 247-Big Bear exit to Lucerne Valley. Left on Highway 18.
Once you are on the mountain:
If you come up # 330 from San Bernardino: Once you see the dam stay on the right side of the lake and follow the road to Big Bear Lake.
If you come up #38 from Redlands: The #38 will bring you automatically onto the Big Bear Boulevard. Follow this road through Big Bear City into Big Bear Lake.
If you come up #18 from Victorville: Once on top of the hill you will see the "Dry Lake". Just follow the road and you will stay to the right of it. Turn left onto Greenway. At the light turn right onto Big Bear Boulevard. Follow this road through Big Bear City into Big Bear Lake.