In every marginal electorate, politicians promise to take revenue raised by nationwide or statewide taxes and spend it on projects that confer purely local economic benefits. This practice is corrupt and unnecessary — corrupt because a minority of taxpayers are bribed at the expense of the majority, and unnecessary because, if a project is economically justified, it can be funded out of the benefit that it confers — and, by implication, from within the area that gets the benefit.
If a project confers a benefit on a limited area, you can’t share in the benefit unless you live or do business in the area; and for that purpose you need access to real estate in the area. Therefore the market value of the benefit is manifested as uplifts in land values in the affected area. If the project satisfies a cost-benefit test, the total uplift will exceed the cost, so the project can be funded by clawing back only a fraction of the uplift through the tax system, leaving the rest of the uplift as an unearned windfall for owners of property in the affected area — and without burdening the taxpayers outside that area.