The growth of autonomous vehicles is likely to happen among users who are already comfortable with ride-hailing services like Uber or Lyft.   Generally speaking, early adopters of technology will be some of the first to embrace self-driving cars, according to findings of a recent study released by the Texas A&M Transportation Institute. The study was sponsored by Lyft, a ride-hailing service currently conducting AV research.   “If you’re one of those who lined up early on the first day that the iPhone X was available — whether you really needed one or not — you’re more likely to be among the first people lining up to use a self-driving car,” said Johanna Zmud, a senior research scientist at the Texas A&M Transportation Institute, and one of the authors of the study, in a statement. “Similarly, if you’re a frequent TNC (transportation network company) customer, you’re more likely to be among the first who routinely use a self-driving car.”   Debate has raged about how readily Americans will embrace self-driving cars. That question has become more significant in the wake of a March 2018 fatality in Arizona when an autonomous vehicle operated by Uber struck and killed a pedestrian.   The TTI study, released this week, shows that by a margin of 2 to 1, frequent users of ride-hailing or ride-pooling services were more likely than non-users of services such as Lyft, Uber or Via to climb into self-driving vehicles. The report was based on a survey of 3,275 people in Boston, Las Vegas, Phoenix and the San Francisco/Silicon Valley region of California, all areas where AV testing is currently occurring. The early adopters of AVs are more likely to be young adults in the 18 to 34 age range, equally split between men and women, childless and middle-income, the research shows.    Consistent with a number of views related to autonomous vehicles, the Texas A&M research shows their introduction into American society will likely be gradual, entering at the “mobility as a service” level where they will become part of a car-service fleet rather than as personal vehicles.   “Generally, shared mobility services were preferred to privately owned vehicles,” the report found. “Our sample was urban and the majority of respondents were current users of ride-hailing services.”   If today’s use of ride-hailing services, which has grown at a meteoric rate, is any indication of the possible growth in autonomous vehicles, then their impact on ride-hailing and car services, roads, and transportation in general could be significant.   Roughly 64.8 million ride-share trips were begun in Massachusetts in 2017, according to the state’s Department of Public Utilities. Some 34.9 million rides originated in Boston, with about 1.8 million of those coming from Logan International Airport, according to the state’s tracking statistics.   Also, as the number of residents in the 18 to 34 age group increased in Massachusetts cities, so did the number of ride-share trips, the state found.   The San Francisco/Silicon Valley and Boston areas are largely considered tech hubs, and are also considered “early adopters” of ride-hailing services, said Zmud. However, cities with a strong tech focus do not always translate into an enthusiastic embrace of ride-hailing.   “Austin, for instance, is a tech-friendly location but use of ride-hailing is low because auto ownership is high,” said Zmud. A 2015 TTI survey of Austin found that only 50 percent of respondents expressed an “intent to use” AV technology. In the latest TTI survey, “intent to use” reached 71 percent of long-term users of ride-hailing services.   The findings by TTI seem to be consistent with Lyft’s own research, which surveyed 67,000 drivers and passengers across 52 cities, and found that 83 percent of Lyft passengers would request a ride in a self-driving vehicle when the service is available, according to the company’s 2018 Economic Impact Report.   “We also found that hundreds of thousands of Lyft passengers have gotten rid of a household vehicle thanks to the availability of ridesharing,” said Gwendolyn (Belomy) Keefe, senior communications manager at Lyft, adding that 50 percent of Lyft users use their car less, and 25 percent say “owning a personal vehicle is less important to them now.”