A passage can be useful enough to become unavoidable. The bridge saves a long journey; the network brings users together; the exchange makes a dispersed market possible. The very achievement that justifies a charge can make refusal expensive. At that point the question changes. The issue is how a society should govern a useful route when the owner's terms cannot readily be checked by another route. The work must still be paid for. The power to decide who may use it, and on what terms, requires an account of its own.
Competition has force where a rival can offer an effective alternative. It is more difficult where duplication consumes resources without adding a comparable benefit. Joskow's account of natural monopoly begins with this cost comparison: over the relevant demand, supplying the service through one undertaking can cost less than dividing it among several. The condition concerns technology, costs and the scale of demand. One large firm is not sufficient evidence of it. Nor does the condition confer a general right to exclude; it identifies a difficulty that any proposed arrangement has to address.
Imagine a passage that costs sixty per period to maintain and another two for each use, including all relevant economic costs. One hundred people each value a single crossing at five. Serving them costs two hundred and sixty and creates a total benefit of five hundred, leaving a net gain of two hundred and forty. If two identical passages divide the same users while each incurs the sixty, total cost rises to three hundred and twenty. Without an improvement in quality, convenience or resilience, duplication has consumed sixty. The obstacle to competition in this example is real, even though nothing in it determines who should own the passage.
A toll equal to the additional cost of a crossing would be two. At one hundred crossings it raises two hundred, leaving the sixty unpaid. Insisting on that toll without specifying how the remainder is financed can make a valuable service impossible to sustain. An equal access charge of sixty cents from each of these hundred identical users, followed by the toll of two, covers the cost. Each user still gains two point four. The arrangement separates the cost of keeping a route available from the cost of using it once more. That separation is a possible solution under the example's assumptions, rather than a reason to ignore the first cost.
Unequal needs make the solution harder. Suppose the hundred users have already financed the passage, and an additional visitor values a crossing at two point three. The crossing would create a gain of thirty cents over its additional cost. Charging that visitor the same sixty-cent access fee as well as the toll would prevent it. A fee that leaves use undistorted among identical participants can deter participation by a person with less to gain. Financing the common cost therefore asks who pays to keep the service available, not merely whether the posted toll matches the cost of the next crossing. A subsidy, a differentiated charge or some other arrangement has consequences and information requirements of its own.
There is also a distributional question even when every original user continues to cross. At a toll of four, the passage receives four hundred and keeps one hundred and forty above its two hundred and sixty in costs. The users retain one hundred in total benefit after payment. Under the cost-covering arrangement they retained two hundred and forty, and the provider retained no economic surplus. Total net gain is two hundred and forty in either case because the service and its use have been held fixed. Reducing this toll would transfer a substantial gain to users without saving that amount in resources. The transfer can be the public purpose; it need not be mislabeled to matter.
Once the charge deters valuable uses, quality deteriorates or resources are spent defending exclusion, more enters the account. So does the return needed to induce a new investment before the passage exists. A rule that takes away every prospective gain from improving the route can change what is built, while a rule that merely reallocates an already available return need not have that effect. Joskow treats pricing, production, investment, quality and distribution as distinct regulatory concerns. A low tariff is therefore one observation about an arrangement, not a complete measure of its performance.
The choice need not be between duplicating an entire system and granting its owner unrestricted control. One can ask which parts of the service need a common facility and which could be supplied by competing firms using it. Opening access then requires terms: a price that contributes appropriately to the shared cost, standards that keep the service reliable, and a way to prevent the owner from favoring its own use. Separation does not eliminate the need for governance. It relocates it to the boundary between the common passage and the activities conducted through it.
Public ownership changes the identity of the claimant, but does not cancel the resource constraint. The publicly owned route still needs maintenance and judgment about investment; its managers still need information about demand and performance. Private ownership under a price rule presents a different set of incentives and information problems. A cooperative places control with a specified group of users, who may disagree about the service and the burden of paying for it. These alternatives should be compared as arrangements people can operate, with costs and purposes made explicit. Calling one of them a market or a public service does not complete the comparison.
Control must also answer to the people whose passage is at stake. An appeal against refusal, a published account of charges, an obligation to explain discrimination between users or a credible alternative route can constrain different abuses. Each proposal needs a mechanism connecting it to the problem. Publishing an account does not itself make entry possible; reducing a charge does not ensure equal treatment; transferring title does not ensure competent operation. These are reasons to specify the remedy carefully. They do not turn the owner's convenience into the measure of the public interest.
The comparison remains open to changes in the underlying costs. A new technology may make a second route economical. Growing demand may support two systems where one formerly served most cheaply. An apparent natural monopoly may instead be an incumbent whose scale is protected by rules or whose costs are above what another provider could achieve. Conversely, opening a route without preserving incentives to maintain it can injure the people it is intended to help. The case for a particular arrangement has to survive these changes, with the quality of the service and the distribution of its gains both in view.
The passage must be sustained; the right to use it must be justified.
The spread ends as a question about the terms of meeting. The middleman may create a route, maintain it and make exchanges possible that would otherwise fail. He may also acquire the ability to decide how much of their gain the parties can keep. A society can recognize the first achievement while governing the second power. What belongs to the builder, what belongs to the users and what must be shared cannot be read from the existence of the toll alone. The next volume turns to the margin at which a further act becomes worthwhile. Here the act has been a meeting, and the price has been the price of arriving. The argument remains open.