From Andrew Odlyzko’s “Pricing and Architecture of the Internet: Historical Perspectives from Telecommunications and Transportation“:
The modern canal era can be said to start with the Duke of Bridgewater’s Canal in England. Originally it was just a means of connecting the Duke’s colliery to Manchester. The parliamentary charter (which enabled him to take over private property, with appropriate compensation) obliged the Duke to carry cargo to Manchester at a maximum charge of 30 pence a ton, and to sell his own coal in Manchester for no more than 80 pence a ton, about half the price that had prevailed before [38,68]. Parliament was determined to obtain substantial benefits for the public from the grant of government powers to the Duke. …
The great financial success of the Duke of Bridgewater’s Canal led to widespread attempts to emulate it. In the early 1790s, there was a canal mania, with a burst of construction that was never to be replicated in Britain. (The U.S. had its canal mania some decades later, following on the great success of the Erie Canal.) The charters of those canals show a general trend towards greater price discrimination. …
Similar toll schedules depending on cargo were also common in the United States. As an example, when parts of the still incomplete Erie Canal were opened in 1820, there was a long list of tolls, concluding with “All articles not enumerated, one cent, per ton, per mile†(Chapter 2 of [81]). The enumerated articles (among those that were measured by the ton) were charged tolls ranging from salt and gypsum at 0.5 cents per ton per mile, to 1 cent for flour, to 2 cents for merchandise, and nothing for fuel to be used in the manufacture of salt (so that it was necessary not only to know the nature of the cargo, but its ultimate use). …
While canal operators were trying to squeeze carriers (who were trying to squeeze merchants, in ways similar to those described below for turnpikes), carriers often attempted to evade tolls. They bribed toll-collectors, misrepresented what the cargo was, or how much there was of it, and in some cases even hid cargo with high toll charges under commodities such as sand for which the fees were low. The countermeasures, just as they are today, and would likely be in the future with electronic communications, were based on both technology and law. Measurements were taken (in many cases there were books available to canal operators, listing canal boats, and the weight of cargo aboard as a function of how deeply in the water they lay), and there were punitive penalties for evasion.