F.1. Organization of surveys at different border points
7.55. Airports The observation of travel flows through airports and their corresponding characteristics and expenditures should be relatively straightforward as the flows are clearly defined (various types of administrative records should be available from the airlines, customs control and airport administration) and travellers have time to answer (either upon departure, after checking in and before boarding; or upon arrival, after disembarking and before leaving the terminal). This makes it possible to interview them at the end of their trip and observe the corresponding expenditures. In some cases, it might also be possible to distribute questionnaires on board the aircraft, before arrival or just after take-off, provided that the airlines cooperate.
7.56. In the case of airports, the statistical design should take into account the information provided by the airlines on anticipated flights, their origin or destination and their capacity and expected number of passengers. On such a basis, and with some assumptions on the proportion of passengers residing abroad or in the country of reference, it is possible to define a sample. For a given flight, some countries might decide to survey all passengers, whereas others prefer selecting respondents, on a quota basis or systematically, or even allow the interviewers to select the persons they interview. For the sake of completeness and accuracy, it is preferable to interview all persons of a selected flight. Quotas, usually based on country of residence, provide skewed results, as the country of residence is not a good explanatory variable of expenditure, if not associated with others, such as duration of stay or purpose of trip. In the case of interviewers selecting informants, the skewing of the results can be all the greater. An additional difficulty may reside in interviewers who do not have access to airline lounges for the conduct of surveys and can only access potential respondents at departure gates. It is suspected that those who use the services of airline lounges have significantly different expenditure patterns from those who do not have access to the lounges, possibly resulting in a serious bias for the estimates.
7.57. Land borders (road) The situation at land borders (road) is very different from that previously described for airports since, frequently, the flows of persons over the border are not well known, either because there is no control at all, such as in the case of countries in the Schengen area, or because control is limited to a certain subset of flows (as in the case of bilateral agreements that facilitate the movements of persons living near the border post) or even because it is impossible for the border control authority to control all border-crossings, legal or illegal. Therefore, it is good practice to measure the flows of persons over the border and to qualify them subsequently as either “visitors” or “other categories of persons travelling”. Such measurement might be done automatically with counting devices that capture vehicles (private cars, buses or trucks), to which an average number of passengers can be imputed, as well as capture their licence plates, from which the country of residence of passengers in private cars can be derived. In the case of buses, a list of passengers and their nationalities is available in most countries.
7.58. Land borders (railways) In the case of land borders crossed on international railways, the case is similar to that of airports. The railway companies should be able to provide the number of passengers and, in some instances, such rough characteristics as a breakdown of passengers into first and second class. A sample could be designed on the basis, for example, of persons seated in a given part of the train, mirroring the design of the satisfaction surveys used by railway companies.
7.59. Cruise ships For some countries, such as those in the Caribbean, persons arriving aboard a cruise ship represent a very significant share of total arrivals and travel expenditure. The number of passengers aboard and their characteristics in terms of residence are known, as well as the characteristics of the crew. In the case of cruise ships, ferries, yachts and all types of recreational vessels, the captain is usually requested to provide the port authority with a list of passengers and crew on board (a manifest), indicating name, surname, nationality, passport number and any additional information that authorities might decide to request. Expenditures in the country visited occur when cruise passengers disembark, although they might also purchase packages on board to visit places of interest. Cruise ships necessarily use specific moorings, and embarking and disembarking are controlled by customs officers. It is good practice to apply a simplified questionnaire, either to all passengers or to a sample, in order to collect information on their expenditure.
Next: F.2. Border surveys and number of mode 4 trips or persons
 Note that many mode 4 persons transit through airport lounges.