cost to the provides of transport services.<sup>3</sup> Collection of high-quality survey data requires well-established sampling and stratification procedures on the universe of shippers or carriers in a country. Conducting it in a comparable manner over regular intervals would help inform changes over time. Such capabilities typically fall within the purview of national statistical agencies. Examples from developed countries showcase the variation in the information that is available depending on survey design. In Canada, the Trucking Commodity Origin and Destination Survey collects information on for-hire trucking industry since 1994, targeting trucking companies with at least one establishment and a minimum annual revenue of about 1 million USD. It excludes foreign-based trucking establishments operating in Canada and private fleets of non-trucking establishments. While it contains data on the revenue of carriers on a shipment basis (including information about the commodity being shipped, weight, distance and destination), it does not report the value of goods shipped.<sup>4</sup> In contrast, the Commodity Flow Survey conducted by the U.S. Census Bureau since 1993 reports the commodity, mode (truck, rail or other modes), weight and travel distance of shipments together with the value of the goods, but does not report freight charges. In Europe, Eurostat’s Road Freight Transport Survey is conducted in EU member countries and Norway since 2012. For around 3 million shipments, it contains information on origin and destination regions, industry of the shipper, the weight of the shipment and the distance covered. While separate vehicle-related, journey-related and goods-related variables inform users about the fleet, itineraries and commodities being shipped, there is no data about freight charges or the value of the goods. For rail shipments, the Carload Waybill Sample is a stratified sample of carload waybills for all U.S. rail traffic collected by the Surface Transportation Board. It includes information about the commodity, origin and destination, weight and freight charges from the sampled shipments. Evidently, each lacking some critical variables, whether any of these surveys is helpful to the user depends on the question at hand. Yet, as will be detailed below, they can be valuable inputs to other methods for imputing or estimate freight costs.

Given the dearth of high-quality surveys conducted and disseminated by national agencies in developing countries, practitioners and researchers combine various datasets on truck fleets and trade flows within countries to get a picture of road transportation— see Allen et al. (2021) for a recent example. An alternative is to conduct a special survey from scratch, possibly with the help of a national statistical agency in sampling from

> 3In principle, balance sheets of transport providers would distinguish their revenues and costs. In practice, however, most transportation providers in developing countries are not publicly listed or even incorporated. Such owner-operators are unlikely to follow rigorous accounting principles and prepare balance sheets.

> 4Behrens et al. (2018) convert freight costs reported in this survey to a percentage ad-valorem measure by using additional information on the value of cross-border shipments by exporters in one wave of the survey.

7