Niles Canyon RD (SR84) is completely closed in both directions between Old Canyon RD and Pleasanton Sunol RD. 
Fremont PD advises that Niles Canyon RD (SR84) is closed due to large landslides, mudslides, and flooding. The closure is for both directions of travel between Old Canyon RD and Pleasanton Sunol RD and will remain indefinitely. Caltrans will reassess road conditions over the next few days.
More information from Caltrans:
Before you get on the road, go to the Caltrans website, and check QuickMap for real-time traffic information, or call 1-800-427-ROAD.
Because visibility is limited and roads will be slick, we are asking all drivers to slow down and allow themselves plenty of time to reach their destinations safely.
Move Over to allow Caltrans crews, CHP, and other emergency personnel to perform the important tasks needed to keep the roads open and quickly respond to emergencies.
Never drive through moving water. And if you see standing water, use caution; it may be deeper than it appears.
For 24/7 traffic updates, follow 511.org: https://twitter.com/511SFBAY. For real-time traffic, click on Caltrans QuickMap: http://quickmap.dot.ca.gov/.
Address/Location
Fremont Police Department (CA)
2000 Stevenson Blvd
Fremont, CA 94538
Contact
Emergency: 9-1-1
Non-emergencies: 510-790-6800