Waymo is operating its self-driving ride-hailing service in two cities: Phoenix, with some paying customers and some riding for free, and Silicon Valley, with just employees as passengers. A majority of riders leave positive feedback about their experiences riding in Waymo’s robot taxis, but there are still some notable complaints, according to internal data reviewed by The Information.

The Information reviewed feedback on 10,500 trips that took place in July and August. Those comments are left by anonymous passengers through Waymo’s mobile app. Most of the rides — 6,100 — took place in the suburbs of Phoenix, with the rest occurring in the Bay Area. Of those 10,500 trips, 70 percent received the highest rating of five stars, while 30 percent were rated four stars or less. That’s down from 40 percent negative complaints from a previous batch of data that was reviewed by The Information. (Anything less than five stars is considered “negative” by Waymo.)

The feedback provides a rare window into the progress at Waymo

The feedback provides a rare window into the progress of the company that is seen as possessing the most advanced self-driving technology on the road today. Despite using public roads, Waymo is not obligated to disclose customer feedback to local regulators. Some of their customers are required to sign nondisclosure agreements to test the vehicles, while others pay for the service and aren’t subjected to NDAs.

Passengers complained about weird drop-offs, circuitous routes, and shaky driving. Others praised the service for navigating tricky traffic situations. (The Information also published a more complete breakdown of the data it reviewed here.) A majority of trips take place with human safety drivers behind the wheel who typically keep their hands in their laps as the vehicle drives itself. Waymo has offered some passengers rides in fully driverless vehicles, with no safety driver but in limited geographic areas.

The complaint rate in Silicon Valley was 47 percent, which is higher than the total complaint rate for the two months’ worth of data. This may be because Waymo encourages its employees to be tough reviewers while using the self-driving taxi service, an unnamed employee told The Information. The terrain in Silicon Valley is tougher than suburban Phoenix, with more density, narrower roads, and more pedestrians and cyclists.

Those conditions could be making it more difficult for Waymo’s vehicles, and passengers are noticing. “That ride was shit!” one Bay Area rider (and Waymo employee) wrote, according to The Information. “Uncomfortable and downright alarming.”

The data highlights the obstacles Waymo will face as it seeks to scale its self-driving taxi service. Experts believe that it will be years before autonomous cars can compete with the convenience and reliability of human-powered ride-hailing like Uber and Lyft.