Mode Substitution
A number of studies that assess the impact of TNC services on modal shift have found that passengers are either: 1) substituting a trip they formerly made with another transportation mode (public transit, driving, walking, biking, etc.) or 2) making a new trip they otherwise would not have made without the availability of TNC services (i.e., induced demand). There are conflicting conclusions regarding the extent to which TNCs compete with public transit. While some studies conclude that TNCs are largely not substituting public transit trips (Feigon and Murphy, 2016; Hampshire, Simek, Fabusuyi, Di, & Chen, 2017; Feigon and Murphy, 2018), several others suggest that a significant portion of travelers substitute TNCs for public transit, biking, and walking (Rayle, Dai, Chan, Cervero, & Shaheen, 2016; Henao, 2017; Clewlow and Mishra, 2017; Gehrke, Felix, Reardon, 2018; NYCDOT, 2018). Past surveys show that the degree to which TNCs substitute for other travel modes varies by city and the built environment. Denser cities like New York City, Boston, and San Francisco exhibited some of the highest proportions of passengers who would have used public transit for their last TNC trip, had TNCs been unavailable. It is important to note that aggregated cross-city studies may obscure city-specific differences in TNC impacts. Also, studies frame questions aimed at parsing modal shift differently. Some ask in a more general manner what transportation mode travelers might have taken instead of a TNC, while others may ask what mode travelers would have used for their last TNC trip. Depending on how this question is presented, responses may be less representative. Additionally, one study (Alemi, Circella, Handy, & Mokhtarian, 2017) allowed respondents to select for more than one mode for how they would have completed their last trip if TNCs were not available. This method allows the percentages of the modes to add up to more than 100%, which makes it challenging to compare results across the studies. The results of existing studies on modal shift are shown in the table on the following page, along with the survey question asked in each study.
Table 7.2 TNC Mode Substitution Impacts Study Authors/ Location/Survey Year of Study Rayle et al.* San Francisco 2014 Henao* Denver and Boulder, CO 2016 Gehrke et al.* Boston 2017 Clewlow and Mishra† 7 U.S. Cities†† Two Phases, 2014–16 Feigon and Murphy‡ 7 U.S. Cities†† 2016 Hampshire et al.** Austin, TX 2016 Alemi et al. ‡‡ California 2015 NYCDOT ‡‡ New York City 2017 Drive (%) 7 33 18 39 34 45 66 12 Public Transit (%) 30 22 42 15 15 3 22 50 Taxi (%) 36 10 23 1 8 2 49 43 Bike or Walk (%) 9 12 12 23 18 2 20 15
Would Not Have
Made Trip (%) 8 12 5 22 1 - 8 3 Carsharing/Car Rental (%) - 4 - - 24 4 - - Other/ Other TNC (%) 10 7 - - - 42 (another TNC) 2 (other) 6 (van/ shuttle) -
* Survey question: “How would you have made your last trip, if TNC services were not available?”
† Survey question: “If TNC services were unavailable, which transportation alternatives would you use for the trips that you make using TNC services?”
‡ Survey crosstab and question, for respondents that use TNCs more often than any other shared mode: “How would you make your most frequent (TNC) trip if the TNC was not available?”
** Survey question: “How do you currently make trips like the last one you took with Uber or Lyft, now that these companies no longer operate in Austin?”
†† The impacts in these studies were aggregated across Austin, Boston, Chicago, Los Angeles, San Francisco, Seattle, and Washington, D.C. ‡‡ These studies allowed multiple responses to the question: “How would you have made your most recent TNC trip (if at all) if these services had not been available?” Therefore, the percentages add up to more than 100 percent, making it challenging to directly compare to the other studies
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Public Transportation
Study findings on TNC impacts on public transportation ridership vary, possibly due to local differences in transit service, urban density, and the built environment. A few studies have investigated the effect that TNCs have on aggregate public transit ridership in U.S. metropolitan areas. Hall, Palsson, & Price (2018) examined the impact of Uber’s entry on public transit ridership between 2004 and 2015 across the 196 U.S. Metropolitan Statistical Areas (or MSAs) where Uber was operating. This study found that Uber is a complement for the average public transit agency, increasing ridership by five percent after two years. A similar study by Feigon and Murphy (2018) examined TNCs and public transit ridership trends in Chicago, Washington, D.C., Los Angeles, Nashville, Seattle, and San Francisco from 2010 to 2016. The authors concluded there was no relationship between the peak-hour TNC trip share and changes in public transit ridership in these cities.
In contrast, Graehler, Mucci, & Erhardt (2019) found that the entry and presence of TNCs cumulatively decreased heavy-rail ridership by 1.29 percent per year and bus ridership by 1.70 percent per year in a study examining data from 2002 to 2018. Gehrke et al. (2018) found that passengers with lower incomes and those who possess a weekly or monthly public transit pass were more likely to have substituted TNC services for public transit. In addition, relatively low TNC service costs, low TNC trip times, poor weather, and unavailability of public transit were also predictive of public transit substitution. Additional research is needed to assess TNC impacts on public transportation ridership, and it is important to account for both aggregate trends and individual modal choices when assessing TNC impacts on public transit.