http://image.wenweipo.com/2011/06/30/20110630hjf0021.jpg The bridge is 36 KM long across a bay in China; it saves _30_ KM travel distance from one side of the bay to another. What a waste!
perhaps, you are talking of Hangzhou Bay Bridge. Wikipedia says "the bridge shortened the highway travel distance between Ningbo and Shanghai from 400 km (249 mi) to 280 km (174 mi) and reduced travel time from 4 to 2.5 hours." So, it is 36 km long and saves 120 km travel distance.
Ah, yes. http://www.telegraph.co.uk/news/worldnews/asia/china/8248197/China-builds-worlds-longest-bridge.html
Billions/ (20 mintues x # of vehicles) x life of bridge in years = ? In turn, minutes can also be translated into liters of fuel.