Route Overview
The Okutadami Silver Line is a 22 km mountain road in Niigata Prefecture, connecting the city of Uonuma to the Okutadami Dam. Originally built for dam construction, it is now open to the public and is part of National Route 352.
This road is unique in that around 18 km of it runs through tunnels, offering a thrilling, cave-like riding experience for motorcycle enthusiasts.
Recommended Section
The full route from Koide Interchange to the Okutadami Dam is recommended.
Riders pass through a series of long, dimly lit tunnels. When you finally emerge, you’re greeted by stunning views of the Okutadami Lake and surrounding beech forests.
Road Conditions and Safety
- Fully paved with relatively wide lanes
- Over 20 tunnels, some with minimal lighting
- Moisture inside tunnels can cause slippery surfaces
- Always ride with headlights on
- Closed in winter (late November to around May)
Points of Interest
- Okutadami Dam: One of Japan’s largest power-generating dams with panoramic lake and mountain views
- Okutadami Lake Cruise: Scenic boat ride on the reservoir
- Ginzandaira Onsen: A quiet hot spring village surrounded by nature
- Okutadami Electric Power Museum: Learn about hydroelectricity and dam construction
Local Foods
- Mountain vegetable dishes and grilled river fish served at mountain huts
- Local soba noodles and dishes made with fresh spring water from the area
Fees and Access
- No tolls on the Okutadami Silver Line
- Nearest expressway exit: Koide IC on the Kan-Etsu Expressway (about 40 min to the entrance)
- No gas stations near the dam — refuel in the Koide area
Best Season and Climate
- Best time to visit: June to mid-October
- Enjoy lush greenery in summer and vibrant fall foliage in autumn
- Tunnel sections remain cool even in summer — bring warm layers
Sample Touring Plan
Day Trip from Niigata (Koide area)
Koide IC → Okutadami Silver Line → Okutadami Dam & Lake → Boat cruise or hot spring visit → Return to Koide (approx. 5–6 hrs)
Overnight Plan
Stay in Ginzandaira Onsen and ride further to the Okutadami Jukai Line or toward the Tadami area the next day