For the past 12 months, hundreds of Arizonans have been helping Waymo develop and perfect its autonomous driving technology.

Dubbed the ‘Early Rider Program’ and established by Google’s self-driving car division, the project provides feedback about what consumers want from an autonomous ride-hailing service.

KTAR News reports that there are currently almost 400 residents in Arizona enjoying rides in self-driving Chrysler Pacifica minivans equipped with Waymo’s tech. Since the program launched in April 2017, more than 20,000 people have applied to be involved.

Waymo’s current early riders are aged between 9 and 69 and have been catching rides to work, school and other day-to-day activities. The company says it has been using their feedback to refine the experience before launching a large autonomous ride-hailing service in the U.S. by the end of the year.

One of the things the technology company has discovered is that passengers often want to ask questions during their rides, but don’t have anyone to ask. As such, Waymo is developing a system that offers one-on-one communication with passengers through a dedicated smartphone app. Additionally, it has started investigating ways to gently rouse passengers who’ve been napping during their journey.

While Google is pushing forward with its plans for a fleet of autonomous ride-hailing vehicles across the country, Uber has been left to play catch up after suspending tests following a fatal crash that involved one of its prototypes in March. Many automakers, such as GM, which is currently working on the technology through its Cruise Automation division, have similar self-driving car ambitions to Waymo.