So now, how do you pay for such a bridge? Suppose we assign the task to government and the government proposed an equal tax of $300 per person which the citizens could vote on? The vote would fail because both B and C would oppose such a tax given that their benefits are lower than the tax. What about a fee for use. You could charge $500 and only A would buy access which would not pay for the bridge. You could charge $250 and both A and B would buy access and $500 would be raised in revenue, still not enough to pay for it. At $200 all three would buy access and $600 would be raised. This is true, by the way, even if you charged it as a per use toll.
What if you asked for voluntary donations? Would A contribute $500? No, if A knew B and C's valuation, A would know that $450 is enough if the others contributed their full amounts. B would know that $200 is enough and C would know that $150 is enough and a total of $850 would be raised. This is known in economics as the free rider problem. This seems a bit contrived in a three person example, so think about a large number of citizens and the free rider problem is clearer: no one individual feels as if their single contribution will make or break the project so many do not donate (think OPB).
So you see, it becomes a real challenge to provide a specific public good. This is why we must empower government to make the purchase for us and it is also why I am generally opposed to taxes for specific goods, the more you tie taxes to specific goods the harder it generally becomes to provide the socially optimal level.
This brings us to the Sellwood Bridge, seen above, which is well past its sell-by date and desperately needs replacement (hopefully before the current one falls into the Willamette). Public good problem? Sure, the local government is struggling trying to figure out how to pay for it. Free rider problem? Yes, again, some local governments are not cooperating on a fee plan. Then there is this letter to the Editor from Eric Fox in The Oregonian today:
Collect toll for new bridge
A toll would solve every problem and argument out there concerning the problems of the Sellwood Bridge. A toll would pay for a new bridge, provide money for future maintenance and repairs and reduce traffic through Sellwood. We could even build a beautiful landmark span (like the St. Johns Bridge) instead of am ugly utilitarian cement hulk. If a Clackamas County citizen or truck driver (truck tolls should be higher) does not want to pay, he can find another route. Only the people who use the bridge would pay for the bridge.
I hate to be a naysayer, but I don' t think this will work, partly because of the theoretical example above and partly because it is pretty easy to substitute other bridges for the Sellwood.
Finally, here is an interesting new wrinkle. I guess my dad, whose old condo (not in the building in the story but in the yellow one above) can be seen in the picture above, sold at the right time: a year and a half ago.