Passenger Value of Time, Benefit-Cost Analysis and Airport Capital Investment Decisions, Volume 2: Final Report (2015) / Chapter Skim
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3 DATA COLLECTION AND MODELING RESULTS This chapter summarizes the Research Team's process of data collection through the development and administration of a stated preference (SP) survey of airline travelers who had made recent domestic air trips within the U.S.
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each respondent by presenting questions and modifying wording based on respondents' previous answers. These dynamic survey features provide an accurate and efficient means of data collection and allow presentation of realistic alternative scenarios that correspond with the respondents' reported experiences.
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The complete set of survey questions as they appeared on-screen is included in Appendix B.1. Trip Characteristics Questions After being presented with basic instructions about how to navigate the computer-based survey questionnaire, respondents were asked a set of screening questions to ensure that they qualified for the survey.
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• Time from security screening to reach the gate area • Time spent in gate area before boarding commenced • Activities performed at the gate • Delay (if any) in departure and arrival of the flight • Scheduled local departure and arrival times • Preferred arrival time • Number of flight connections or stop-overs • Connection airport(s)
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• Air carrier • Departure and arrival time • Type of aircraft • On-time performance of the flight(s) • Average amount of delay for delayed flights Factors related to airport access, time spent in the airport terminal, or other non-flightrelated factors were intentionally excluded to focus the respondent on the attributes relevant to the choice between different flight itineraries, in particular airfares, flight time, the number of connections, and expected delay.
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2) [Base flight time *
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These levels were chosen to fall within the range of typical flight connection times, but also to present differences large enough to encourage respondents to trade-off against the attribute. Air Carrier.
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groups were flights less than two and a half hours, flights between two and a half and four hours, and flights greater than four hours. Flights with a base flight time of less than two and a half hours were presented with the following aircraft types: 1)
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Table 6 summarizes the attributes and levels used to generate the alternatives in the flight itinerary choice experiments.
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Table 6. Stated Preference Attribute Levels– Flight Itinerary Choice Experiments Attribute Level Calculation Airport-to-airport timea 1 [Base flight time *
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b Arrival time and departure time were validated to ensure that flights were not shown to arrive or depart between the hours of 12:00 AM and 6:00 AM. If a calculated departure or arrival time did fall within this period, the flight itinerary was shifted earlier or later to avoid this period.
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with waiting to check-in would be different from the disutility for waiting for security screening. • Time to Reach the Gate Area: The time spent traveling to the gate area after clearing security.
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4) 15 + reported access time *
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The final design was evaluated by the Research Team, checked for correlation, and adjusted to eliminate stated preference experiments where one alternative would be clearly dominant over the other, which would result in little useful information obtained from that experiment. Table 7.
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Attitude and Air Travel Background Questions After completing the two sets of stated preference choice experiments, respondents answered a series of attitude questions that asked the level to which they agree or disagree with five statements related to how they buy air tickets and their general air travel attitudes. Next, they were asked about the number of round trips they have made by air within the U.S.
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These differences can then be reflected in the structure and coefficients (value of time estimates) of the resulting choice models.
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3.3 Survey Results A total of 1,260 respondents completed the online survey, including 105 responses from the soft-launch in February and 1,155 from the full launch in April. The number of records was reduced to 1,171 after completing data checks and outlier analysis during the model estimation work, which is described in more detail in Section 3.4 (Model Estimation)
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Figure 4. Ticket Acquisition Method by Market Segment Overall, the majority of respondents reported that they personally paid for the air ticket (77%)
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Figure 6. Distribution of Reported Airfare Overall, respondents reported 172 distinct origin airports and 148 distinct destination airports throughout the country.
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Figure 7. Location of Origin Airports by Number of Reported Trips Figure 8.
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Table 10. Comparison of Top 5 Origin Airports with DB1B Data Airport Sample Originating Passengers Sample % DB1B Originating Passengers DB1B % Chicago O'Hare International (ORD)
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Figure 10. Length of Stay by Market Segment Table 12 shows respondents' access modes to the airport.
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origin and origin airport were used to calculate the airport ground access distance using a Google Maps driving directions algorithm. Respondents also reported their ground access time to the airport.
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Figure 12. Distribution of Reported Time to Security Screening from Entering the Terminal Figure 13 shows the distribution of the time it took respondents to clear security, including time spent waiting in line, placing hand baggage and other items on conveyer belts, and progressing through any mechanical and/or personal screening systems.
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Figure 14. Distribution of Reported Time to Reach the Gate Area from Security Finally, Figure 15 shows the distribution of the time that respondents reported spending after reaching the gate area until flight boarding commenced, termed the gate time.
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encountered delays and the actual time that it took them to reach the gate, which is generally less. Airlines commonly advise passengers to arrive at the airport at least an hour before their flight, although it often takes much less than that to reach the gate area.
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to arrive more than an hour earlier than their actual arrival time, whereas only 6% would have preferred to have arrived more than an hour later than the actual arrival time. The distribution is somewhat similar for both business and leisure travelers.
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Table 14. Respondents' Airline Preference Airline Survey Respondents Including Airline in Set of Preferred Airlines Southwest Airlines 602 Delta Airlines 597 United Airlines 464 American Airlines 381 JetBlue Airways 244 US Airways 233 Alaska Airlines 139 Continental Airlines 139 AirTran Airways 135 Frontier Airlines 107 Virgin America 101 Hawaiian Airlines 84 United Express 54 Delta Connection 50 Allegiant Air 35 Air Canada 34 US Airways Express 20 Sun Country Airlines 19 America West Airlines 17 Horizon Air 17 American Eagle 16 Spirit Airlines 13 Express Jet 4 SkyWest Airlines 3 WestJet 3 Atlantic Southeast Airlines 1 Cape Air 1 Questions on Attitudes to Air Travel and Recent Experience Upon completing the stated preference experiments, respondents were asked to answer a series of questions related to their attitudes about flight itinerary selection and their general level of experience with air travel.
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likely to fly less for environmental reasons, as shown in Figure 20. Respondents also indicated they generally shop for the cheapest flights and do not consider other factors (48%)
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standard memberships for their preferred airlines. For the respondents' most preferred airline, approximately 85% of business travelers and 80% of leisure travelers were members of a frequent flier program.
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nationwide, current demographic distributions for air passengers making domestic air trips to use as a point of comparison. There are also pronounced longitudinal trends in the air travel passenger mix that will not be apparent from current demographic data.
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(MNL) model20 for the two traveler market segments of those making business and those making personal trips.
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After completing the data cleaning and outlier analysis, a total of 1,171 survey responses were used to conduct the discrete choice model estimation and specification testing for the flight itinerary choice experiments and 1,072 survey responses were used to conduct the discrete choice model estimation and specification testing for the airport time components choice experiments.21 Multinomial Logit Model Estimation and Specification Using the cleaned dataset, several discrete choice model specifications were tested to explain the respondent choices in both the flight itinerary and the airport time components choice experiments. The statistical estimation and specification testing were completed using a conventional maximum likelihood procedure that estimated a set of coefficients for a multinomial logit (MNL)
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It is not immediately obvious why someone in a multiple-person party would have a higher WTP than someone traveling alone, other factors being equal. However, it is possible that some respondents making an air trip with others were paying the airfare for the other members of the travel party as well as their own and took this into account in making tradeoffs between airfare and travel time.
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carrier) if this was not either of the three most preferred airlines.
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specific and the units must be accounted for when comparing coefficients (units are specified in Tables 15-22, below)
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Table 15. MNL Model Results – Flight Itinerary SP Experiments (Business Trips)
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Table 16. MNL Model Results – Flight Itinerary SP Experiments (Leisure Trips)
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Table 17. MNL Model Results – Airport Time Components SP Experiments (Business Trips)
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Table 18. MNL Model Results – Airport Time Components SP Experiments (Leisure Trips)
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Table 19. MNL Model Results with Individual Income – Flight Itinerary SP Experiments (Business Trips)
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Table 20. MNL Model Results with Individual Income – Flight Itinerary SP Experiments (Leisure Trips)
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Table 21. MNL Model Results with Individual Income – Airport Time Components SP Experiments (Business Trips)
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Table 22. MNL Model Results with Individual Income – Airport Time Components SP Experiments (Leisure Trips)
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are consistently higher for each time component as compared to the corresponding values for leisure travelers. Additionally, there are considerable differences in WTP values for various time components.
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Table 24. Willingness-to-pay Values (in $/hour)
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3) Higher WTP values found for savings of time spent in the airport terminal compared to time spent in ground access.
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The following sections of this chapter summarize the findings of the additional analysis undertaken to address the foregoing issues: • Comparison of survey respondent reported flights to national data • Comparison of survey respondent air party characteristics to airport survey data • Further analysis of survey results and model estimation • Comparison of ground access coefficients estimated from survey data with ground access mode choice model coefficients in prior studies A more detailed discussion of the analysis undertaken to address each of these topics is included as Appendix B.3 to this report. Comparison of Reported Flights by Survey Respondents to National Data Since the objective of the SP survey was to obtain a representative sample of air travelers who had made a recent domestic air trip, the extent to which the reported air trips in the survey correspond to the distribution of domestic air travel across different markets has important implications for how representative the survey results are for domestic air travel in general.
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reported trips. Only 10% of the markets that were included in the survey trips were over-sampled by more than one reported trip and the largest over-representation was only four survey responses.
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characteristics in an intercept survey will therefore reflect a higher presence in the survey sample of travelers who make more frequent air trips, since they have a higher likelihood of being surveyed. This will affect the observed distribution of those characteristics (such as household income)
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year without any further breakdown by purpose, so it is unclear how the lower proportion of non-business trips reported by the SP survey respondents relates to the various trip purpose categories in the LAX survey. The lower proportion of business trips in the LAX survey may also reflect the timing of the survey, which was conducted in two waves with the first wave in late August, as well as the importance of Southern California as a vacation destination.
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Further Analysis of Survey Results and Model Estimation The Research Team undertook additional analysis of the survey results and model estimation. Some of the issues were resolved while others will require further research beyond the current project to fully address.
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this analysis. An attempt to estimate WTP values for flight delay using a non-linear function of expected delay also gave inconclusive results, suggesting that further research with a larger survey sample size may be needed in order to capture any such effects.
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8) Pending the results of future research to clarify and extend these findings, the estimated relationships provide a basis for incorporating a continuous function of income into air traveler choice models in order to account for differences in income when exploring the effect of other variables, as well as adjusting WTP values in airport BCA studies to account for changes in income distribution.
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Since these models were estimated on data collected at different points in time, adjustments were made so that the resulting estimates of WTP were expressed in consistent dollars to the values estimated from the SP survey data, allowing for both inflation and changes in real household income over time using the national consumer price index published by the Bureau of Labor Statistics. In comparing the WTP values given by the SP survey experiments with those given by the prior studies, it should be borne in mind that the five metropolitan regions covered by the prior studies had an average income in 2012 (weighted by population)
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obtained from the SP survey experiments. Lastly, it must be recognized that air passenger surveys and mode choice modeling primarily concerned with airport ground access can address a wider range of factors, including ground access modes not considered in the SP survey experiments, than a survey that spans the range of travel time components associated with an air travel trip.
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travelers have a higher average income than travelers in general, it could be expected that the VTTS for airport ground access trips would be higher than for local travel in general. • The values for business travel in the U.S.
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or revealed preference (RP) methods.
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The value for flight time (which includes in-aircraft time and time spent making any flight connections) is estimated to be the highest among all the time components ($51 per hour for business travelers and $35 per hour for leisure travelers)
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income in the prior year to the survey) may not have significantly affected the resulting WTP values.
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