Double Spiral Bridge

A fascinating bridge in Japan.

Many innovations seem only to appear where there is a really unusual need, warranting an unusual solution. The Kawazu-Nanadaru Loop Bridge in Japan is one such example: How do you build a bridge from one mountainside to another when the sides of the mountain are so steep that it is not possible to build a road at the same elevation on both sides? This double spiral brings cars up and down a full 45 meters (148 feet) while being seemingly suspended in a valley between two mountainsides.

Some other stats:
- 1.1 km long
- 80 meters in diameter
- speed limit: 30 km/h

Coming upon this bridge in the middle of this mountain road is quite an experience. The bridge was finished in 1982 and has become a popular landmark on route 414 heading south from Tokyo towards the hot spring resorts of the Izu peninsula.

The only way for traffic to get down the mountainside into the valley, too steep for any other usual road-building solutions.

The busy Route 414 serves the weekend crowd from Tokyo, intent to wind down at the hot springs resort of the Izu Peninsula. The “winding down” bit obviously starts at this bridge. The double-spiral structure demands careful driving – the speed limit on the bridge is only 30 km/h, which also helps to better enjoy.