1. 1,400 Michigan bridges need fixing; spans rated 13th worst BY MATT HELMS Detroit Free Press http://www.freep.com/article/20110329/NEWS06/103290345/1-400-Michigan-bridges-need-fixing-spans-rated-13th-worst?odyssey=mod|newswell|text|FRONTPAGE|p

2. Michigan’s deficient bridges More than 13% of Michigan's highway bridges are structurally deficient, a number that will only grow as thousands of spans statewide approach their 50-year life expectancy, transportation leaders warned Monday. With about 1,400 bridges labeled structurally deficient by federal standards, Michigan ranks 13th worst in the nation in the number of bridges in poor condition, according to a report released Monday by Transportation for America, a transportation advocacy group. The national average is 11.5%.

3. Structurally deficient Michigan's nearly 11,000 highway bridges are, on average, 41 years old. About 185,000 U.S. bridges are 50 or older, and that number could double by 2030. A label of "structurally deficient" doesn't mean a bridge is unsafe, but rather that it's showing wear and tear, and needs repair. Michigan Department of Transportation Director Kirk Steudle said during a news media briefing Monday that bridges in that category are inspected more frequently and would be closed immediately if they posed a risk to drivers. "If the bridge is open, the bridge is safe," Steudle said. "We take that very seriously.

4. Sources of revenue Supporters have tried for years to boost highway spending in Michigan, but the effort hasn't gained traction in the recession-battered state. Gas taxes and vehicle registrations are the primary source of road funding in Michigan. The state's gas tax, 19 cents a gallon, was last raised in 1997. Michigan is hardly alone in being too broke to keep up with bridge repairs. Transportation for America said a broader national study it will release Wednesday found one in nine U.S. bridges in poor condition. Michigan was one of 23 states with more structurally deficient bridges than the national average.

5. Depreciation Loss of economic value. 50 year life expectancy  depreciation rate of 2% per year. What do we do to address impacts of depreciation?

6. Tolls Collected Optimal Size Look at # of cars/hour. # of cars/hour demand $ Demand … and supply. AC MC Why is MC > AC at some times of day? Optimal quantity is Q*. Optimal toll is t*. t* Q*