Sunday economics

Scarcity is not the only source of value:

Internet: 11/29/2007: Daniel Hall: The progressivity of congestion pricing

Common Tragedies Blog:
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As anyone who's ever relied on a bus transit system can attest, the value of the system is strongly related to the density of the service - both the number of routes and the frequency of service along routes. And as Leape points out, as the service becomes more valuable, more people flock to it, lowering unit costs and making it easier to provide even more and better service.

Mass transit systems are a network good with positive externalities - beyond reducing congestion, buses are a far less polluting alternative than cars - and hence should be subsidized to achieve the socially optimal level of provision. Public roads, on the other hand, are a common pool resource whose value is rapidly degraded when given away for free.
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