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39 SURVEYS OF AIRPORTS, PLANNING AGENCIES, AND OTHER ORGANIZATIONS To better characterize the current state of practice with air- port access mode choice models, as well as to identify mod- els that may been developed for specific studies but not reported in the published literature, a survey was undertaken of airport authorities, regional and state planning agencies, federal agencies involved in airport or surface transportation planning, airport consulting firms, selected universities and other research organizations, and relevant industry associa- tions. The survey enquired about recent airport ground trans- portation studies undertaken by the responding organization and whether these involved the use of formal models of air- port ground access mode choice. The survey also enquired about respondentsâ perceptions of the usability of such mod- els, as well as their awareness of other organizations that have experience with the use of these models. A list of potential survey recipients was developed and reviewed with the Project Panel. This list was comprised of all U.S. large hub and medium hub airports in 2005 (defined by the FAA as those enplaning more than 1% and 0.25% of total U.S. enplaned passengers, respectively), as well as the eight largest Canadian airports, together with a sample of 47 MPOs and the aeronautics or aviation agencies for each state. Three of the state aviation agencies (Hawaii, Maryland, and Rhode Island) are also responsible for operating large or medium hub airports included in the sample and were not surveyed separately as state agencies. The sample of MPOs comprised all of those responsible for regions with a Metro- politan Statistical Area population in 2003 of one million or more, because those were felt to be the most likely to become involved in airport ground transportation planning. Although the hub size definition used by the FAA is based on enplaned passengers rather than originating passengers (who use the ground access system), those airports with a high proportion of connecting passengers are generally the larger airports that also generate a large amount of ground access trips. In addition, the survey recipients included 42 consulting firms involved in airport planning studies and 17 academic and other researchers who were known to have an interest in airport ground transportation studies, as well as selected key staff in four federal agencies involved in airport ground transportation issues: the FAA, FHWA, FTA, and Volpe National Transportation Systems Center. The survey was also sent to three industry organizations representing airport operators, airport consultants, and airport ground transporta- tion operators. In addition to the survey recipients on the mailing list, an e-mail request was sent to the chairs of several TRB committees with a scope relevant to airport ground trans- portation or transportation modeling issues. The e-mail de- scribed the scope of the study and asked them to forward the information to the members and friends of their com- mittees and invite any with relevant experience to partici- pate in the survey. This generated a number of additional survey responses. Four slightly different survey questionnaires were devel- oped reflecting the different concerns and needs of the various types of organizations included in the survey. In addition to the online versions of the survey, the four questionnaires were pre- pared as Microsoft Word documents that could be downloaded from the TRB website and completed off-line. Survey recipi- ents were given the option of responding to the survey by downloading the appropriate version of the questionnaire and returning it by e-mail, fax, or mail. The four questionnaires are found in Appendix A. A memorandum from the ACRP staff officer responsible for the project was sent by e-mail to each survey recipient requesting their assistance with the project by participating in the survey and providing a link to the online survey and the Word version of the questionnaire. The memorandum requested survey recipients to respond within approximately 3 weeks of the initial requests. A reminder e-mail message was sent at the end of this period to those survey recipients who had not responded and several follow-up messages were sent over the subsequent weeks. Survey Response As of July 2, 2007, 107 responses representing 105 different organizations were received. The composition of the re- sponses is shown in Table 1. The overall response rate to the survey was approximately 43%. The response rate varied across the different types of organizations, from a response rate for large hub airport au- thorities, MPOs, and airport planning consultants of around 50% to a response rate for research organizations of approx- imately 30%. The response rate for state aviation agencies CHAPTER FOUR USE OF AIRPORT GROUND ACCESS MODELS IN AIRPORT PLANNING
was approximately 35%, whereas that for medium hub air- ports and federal agencies was approximately 43%. One MPO forwarded the survey request to its state DOT, which does the transportation modeling for the MPO. The resulting response has been included with the MPO responses. The overall response to the survey was believed to be rea- sonable, given the specialized nature of the topic and the diverse composition of the sample. It is likely that those or- ganizations with the most experience with airport ground access modeling would have been more inclined to respond, and indeed many respondents provided valuable informa- tion. However, the relatively small number of responses in any category limits the ability to draw any statistically robust conclusions from the survey results for different types of organizations. Nevertheless, it is believed that the survey provides a reasonable profile of the extent to which airport ground access mode choice models are used in airport land- side planning and some indication of how this varies across different types and sizes of organizations. SURVEY FINDINGS In view of the limited number of survey responses for each type of organization, the survey findings are presented for all respondents combined, although the role of each type of organization is somewhat different. Where there appear to be significant differences between the responses to a given question across the different types of organizations this is discussed in terms of the actual count responses. Number of Airport Ground Access and Airport Choice Studies Of the 105 organizations responding to the survey, 57 (53%) reported that they had sponsored, undertaken, or participated 40 in studies over the past ten years that included some analysis of airport ground access mode choice. The proportion of dif- ferent types of organizations that reported some involvement in ground access studies varied considerably. Perhaps not surprisingly, most large hub and equivalent Canadian air- ports (13 of the 14 responding), airport consulting firms (20 of 23 responding), and researchers (6 of the 7 respond- ing) reported involvement in studies of this nature. In the case of airport consulting firms and researchers, this may reflect that those organizations with experience of this type of study would be more likely to respond to the survey. MPOs and state aviation agencies reported a much lower level of involvement in such studies, with only 8 of the 24 MPOs that responded to the survey and only one of the 16 state aviation agencies reporting any involvement. The survey responses identified 103 specific studies, to- gether with some references to other studies that were too vague to identify the specific studies in question. Some responses mentioned air passenger surveys. However, these are not considered analytical studies in the sense intended by the question and are not included in the count. Several of the respondents appeared to be referring to the same study and after eliminating duplicate references the responses identi- fied 85 separate studies, ranging from airport master planning studies through feasibility studies for improved airport ground transportation services to academic studies of air pas- senger ground access mode choice. A significant number of these studies have not previously been reported in the literature, at least in a way that would allow a typical literature search to identify them as being rel- evant to airport ground access mode choice analysis. There- fore, the survey has been very valuable in identifying a broader range of airport ground access studies than is gener- ally reported in existing bibliographic reviews of airport ground access issues. Type of Organization Sample Size Sample Responses Other Responses Total Responses Airport Authorities Large hubs Medium hubs Other (Canadian) 26 35 8 13 15 3 Subtotal 69 31 1 1 32 Metropolitan Planning Organizations 47 23 2 25 State Aviation Agencies 47 16 16 Federal Transportation Agencies 7 3 3 Airport Planning Consultants 42 21 3 24 Research Organizations 17 5 2 7 Industry Organizations 3 0 0 Total 232 99 8 107 TABLE 1 SURVEY RESPONSE
41 The survey also asked respondents whether their organi- zation has undertaken or participated in studies over the past ten years that have included some analysis of air passenger airport choice. Of the 105 organizations responding to the survey, 37 (35%) reported some involvement in such studies. Respondents identified 32 separate studies. Although it appears from the titles of the studies that several may not be airport choice studies in the sense intended by the question, the responses identified a number of studies that have not been previously reported in the literature. Use of Analytical Models Respondents were asked to state whether any of the studies involving some analysis of airport ground access mode choice made use of formal analytical mode choice models. Of the 57 respondents reporting such studies, 34 (60%) indi- cated that the studies involved such models and specifically identified 52 of the 85 separate studies previously reported. Thus, it appears that the use of formal mode choice models in airport ground access studies is quite widespread. The survey also asked whether any of the studies involv- ing analysis of airport choice made use of formal analytical models of airport ground access mode choice as a factor in airport choice decisions. Of the 37 respondents reporting such studies, 15 (41%) indicated that the studies included the use of such models and specifically identified 16 separate studies. However, three of these studies were updates of a regional transportation planning process by the same organi- zation using the same model. Respondents who indicated that airport ground access studies included the use of formal analytical models of mode choice were asked about the source of air passenger survey data used in the development of the models. Of the 34 re- spondents reporting studies involving the use of such mod- els, 23 (68%) indicated that the models utilized data from surveys performed specifically for model development and an equal number indicated that the models used data from surveys performed for other purposes. Multiple responses were possible from a given respondent, because their re- sponses could cover more than one study or a given study could use data from more than one survey. The survey asked those who reported involvement in air- port ground access studies that made use of formal analytical models of mode choice whether reports from any of these studies are available on their organizationâs website. Only five respondents indicated that this was the case, one airport authority, two MPOs, and two universities. Further investi- gation established that the airport authority website was an intranet site that is not accessible to the general public. The survey also asked whether reports on the air passenger sur- vey data used in the development of the mode choice models are available on the responding organizationâs or another organizationâs website. Only five respondents (not the same five) indicated that this was the case. Thus, it appears that the majority of the studies identified in the survey are not readily available from the Internet and direct follow-up with the sponsoring organizations would generally be necessary to obtain documentation on these studies. To determine if the use of analytical mode choice models may have increased in recent years, as well as to identify ex- perience that may not have been reported because it occurred before the ten-year period mentioned in the earlier questions, respondents from airport authorities and MPOs were also asked if their organization had undertaken or commissioned studies prior to the last ten years that made use of formal analytical models of airport ground access mode choice. Of the 55 organizations responding to this question, 9 (16%) indicated that they had and 29 (51%) indicated that they had not. A further 17 were not sure whether they had or not. Therefore, of the 38 respondents who knew whether such studies had been done, only approximately 24% reported the use of such models in earlier studies. This is not significantly different from the percentage reporting the use of such mod- els in studies undertaken during the past ten years (13 re- spondents out of 56 organizations, or approximately 23%), particularly because those who were not sure or did not answer the question may well be less likely to have under- taken such studies than those who knew either way. There- fore, there does not appear to have been a significant increase in the use of analytical models in recent years. Satisfaction with Existing Models The survey asked those respondents who reported the use of formal analytical models of airport access mode choice how they would characterize the current state of practice with such models based on their organizationâs experience. Of the 34 organizations that reported experience with the use of such models, 19 (55%) indicated that current models were adequate for their needs, 12 (35%) indicated that cur- rent models are not reliable enough, 3 (10%) indicated that current models are too complex to use, and 10 (30%) indi- cated that they are too costly to use (multiple responses were allowed). Although on its face this suggests a generally high level of satisfaction with the current state of practice, it is noteworthy that seven of the eight airport authorities and all five of the MPOs reporting the use of such models indicated that current models are adequate for their needs, whereas only 5 of the 13 consulting firms reporting involvement in studies using such models indicated that current models are adequate. Because in many cases the studies using such models are performed by consultants rather than the airport authority or MPO staff, and the consultants may well be reluctant to share any con- cerns about the adequacy of the analysis with their clients, this may suggest that the apparent confidence in the current
models by the airport authorities and MPOs could be mis- placed. It is also possible that the definition of what is con- sidered adequate varies among the different organizations. Those respondents that reported undertaking or being in- volved in airport ground transportation studies that included some analysis of airport ground access mode choice but did not make use of formal analytical models of mode choice were asked for the reasons that the studies did not include the use of such modeling. Of the 22 organizations in this cate- gory that answered the question, 15 (70%) indicated that the scope of the studies did not require it, 4 (20%) indicated that there is inadequate information and guidance on the use of such models, and 3 (15%) indicated that available models are not reliable enough or too difficult to use. An additional five respondents indicated that the decision on which analytical techniques to use either was made by those performing the study or they did not know the reason. Modeling Airport Trips in Regional Transportation Planning Process Of the 23 MPOs that responded to the question about how they modeled airport trips in their general regional travel modeling process, 15 (65%) reported that they modeled air 42 passenger trips using a special-generator sub-model, 5 (20%) reported that they treated air passenger trips the same way as other home-based non-work trips, and another 5 reported that they treated air passenger trips the same way as other non- home-based non-work trips. Six MPOs (25%) reported that they modeled airport employee trips using a special-generator sub-model, whereas 12 (50%) reported that they treated air- port employee trips the same way as other journey-to-work trips. Three MPOs reported that they modeled air passenger trips in the regional travel modeling process but not airport employee trips, whereas four other MPOs reported that they modeled airport employee trips but not air passenger trips. One MPO reported that airport automobile driver trips were modeled using exogenous trip tables that are developed from air passenger survey data. Future year trip tables are developed using a Fratar-type extrapolation technique (Fratar et al. 1954; Papacostas 1987) based on future year household and employment forecasts. In summary, this tech- nique extrapolates a base year trip table to a future year by initially applying growth factors to each zonal interchange flow based on the forecast change in the characteristics of each zone and then iteratively calculating adjustment factors and applying them to the zonal interchange flows so that the flows into and out of each zone balance.
