plank road

The plank road was a road surface made by laying wooden planks across two lines of timber, introduced in the United States as an answer to the rutted local roads that isolated rural communities from markets. It offered real, immediate gains: travel between towns could take half as long, the surface remained usable in different weather, and farmers could reach customers farther away. But its commercial promise rested on a mistaken estimate of its durability. As plank-road companies multiplied, their apparent success helped spread the belief that the system worked; when the planks wore out after roughly four years, the investment proved unsustainable. The rise and failure of the plank road became a telling example of an information cascade, in which people treat others’ choices as evidence even as the decisions they imitate cease to reflect independent knowledge.

A road for rural communities

Canals and railroads linked major towns and cities, but they did little for most Americans living beyond those routes. Local public roads, maintained in separate stretches by villages, were often poorly drained and badly surfaced. In wet weather they became muddy ruts; in dry weather, dusty ones. Travel was slow and hard on both vehicles and the animals pulling them. The plank road promised a direct improvement to this everyday bottleneck: a built surface that could connect smaller places to one another and to larger markets.

The idea had arrived from Canada, where plank roads had been introduced in the early 1840s. After seeing evidence of their success there, engineer George Geddes became convinced they could work in the United States. The construction was straightforward in principle: wooden planks laid over two lines of timber. The key uncertainty was not whether this surface was better than a muddy track, but whether it would last long enough to justify the cost of building and maintaining it. Since most roads would be privately owned and supported by tolls, durability determined whether the improvement could also be a viable business.

Geddes’s forecast and the boom

In 1846, Geddes persuaded fellow townsmen in Salina, New York, to charter a company to build the state’s first plank road. He expected a typical road to last eight years, a lifespan he considered long enough to provide a reasonable return on investment. The road proved a roaring success, and roads built soon afterward also appeared to confirm the model. Their benefits were tangible: they cut travel time between towns in half, could be ridden on in any kind of weather, and allowed small farmers to extend the markets for their goods.

The success in Salina helped turn a local construction project into a national enthusiasm. Plank-road fever spread through New York, then the mid-Atlantic states and the Midwest. Geddes became a spokesman for the industry, while promoters in other states helped advance the same cause. Within a decade, New York had 352 plank-road companies, and the United States had more than a thousand. Each new road offered a visible demonstration of the idea and made the next one appear more credible. The roads solved a real problem, and that real usefulness made the optimistic claims about their longer-term prospects easier to believe.

The durability failure

The central commercial assumption was wrong. Plank roads did not last the eight years Geddes had forecast, nor the twelve years some other enthusiasts suggested. Their actual lifespan was closer to four years. At that rate, maintaining them cost too much for the companies responsible for them, undercutting the economic rationale for the toll-supported roads.

By the late 1850s, it had become clear that the plank road was no transportation panacea. A few survived for decades longer: a thirteen-mile stretch along what is now Route 27A in Jamaica, Queens, remained in operation until the 1880s. But such exceptions could not rescue the system as a whole. By the end of the Civil War, almost all plank roads had been abandoned. The contrast between rapid expansion and widespread failure turned the roads’ short working life into more than a construction defect: it was the fact that the movement’s early successes had not established the durability on which its investment case depended.

An information cascade

The plank-road boom illustrates an information cascade: people making decisions in sequence infer from the choices of those before them, and may set aside their own private information as a result. The mechanism does not require simple conformity or a desire to copy a fashionable neighbor. In the cascade account, people imitate because they believe earlier choices carry useful information. The first roads seemed to offer precisely that evidence. Every new road could be read as another sign that the model had been tested and found worthwhile, while the growing number of roads made alternative solutions seem less plausible.

The account’s restaurant example clarifies how a cascade can produce a mistaken collective choice. Suppose a group must choose between a better Indian restaurant and an inferior Thai restaurant, while each person receives imperfect information about which is best. If the first few diners happen by chance to receive misleading information and choose the Thai restaurant, later diners may see its crowd as evidence of quality. Even someone whose own information favors the Indian restaurant may conclude that the Thai restaurant is more likely to be better. The group can therefore choose incorrectly, not because nobody has information, but because later choices are based on an interpretation of earlier choices rather than on each person’s own signal.

The same logic explains both the appeal and the weakness of plank-road fever. Early roads produced visible benefits, so the confidence they inspired was not baseless: faster journeys and access to wider markets were genuine improvements. Yet those immediate gains could not establish how long the planks would last. As construction spread, people had increasing reason to suppose that others had already resolved the unanswered question. After enough people stopped relying on their own knowledge, the cascade ceased to aggregate independent information. Each person assumed the earlier builders had evidence; later builders followed the apparent consensus, although that consensus increasingly reflected imitation of presumed evidence rather than fresh knowledge. The result was a collective decision to spend heavily on roads whose true lifespan made them too costly to maintain.

Competing accounts of how ideas spread

The cascade model is not the only explanation of how new ideas gain momentum. In The Tipping Point, Malcolm Gladwell emphasizes particular kinds of influential people—mavens, connectors, and salesmen—and describes the spread of ideas in terms of social ties. In the model associated with Sushil Bikhchandani, David Hirshleifer, and Ivo Welch, by contrast, individuals are assumed to have equally good private information. Early adopters become influential not because they are unusually connected or knowledgeable, but because their decisions happen first and are therefore visible to everyone who follows.

These accounts distinguish two routes by which people seek guidance: observing the choices of those who came before, or relying on people believed to possess a special kind of information. In the plank-road case, the widening network of roads made the technology look increasingly established, while the roads’ visible advantages helped explain why that judgment seemed reasonable. The later abandonment exposed what the cascade had obscured: widespread adoption was not proof that the original eight-year forecast was sound. The plank road thus stands both as a short-lived transport improvement and as a case in how a group can mistake the accumulated appearance of confidence for the independent confirmation of a claim.