Uber has announced that it will begin selling train and bus tickets through its app for its customers in Denver, Colorado. It’s the first step in the ride-hailing giant’s high-stakes quest to become the de facto smartphone app for all modes of transportation, not just cars. It’s Uber’s chance to blunt some of the negative effects its rising popularity has had on public transportation.

Following a staggered rollout, residents of Denver will be able to use Uber’s app to purchase tickets for the Regional Transportation District (RTD), which operates the city’s buses and trains. Purchasing transit tickets via Uber will cost the same amount as through existing options, the company said.

Uber’s app will let users purchase and redeem a range of tickets, including three-hour, day, and monthly passes. Users activate tickets, which are stored in the “Transit tickets” section of the app, when boarding a bus or train. Once purchased, tickets are available even when your phone is offline.

Uber’s new transit feature is powered by Masabi, a London-based tech company that builds mobile ticketing software for public transportation. This is the first incarnation of Uber and Masabi’s partnership since the two companies first struck a deal last year to integrate the latter’s mobile ticketing platform into the former’s app. Uber riders in Denver have been able to see real-time bus and rail information when they open the app since January, courtesy of transit data firm Moovit.

The news comes just days before Uber’s hotly anticipated IPO at a record-breaking valuation of $90 billion. For years, the company has faced criticism for its negative effects on public transportation in the US. Declining bus and subway ridership has been pegged to the rise of Uber’s popularity in dozens of cities. The company hopes to blunt that criticism by giving transit equal footing in its app.

The problem is that many experts see Uber as being in direct competition with public transportation. In fact, the company admitted as much in its S-1 filing with the US Securities and Exchange Commission that is required as part of Uber’s IPO. The company described public transportation as part of its “total addressable market,” a term it defined as how it can make money over the long term. Under the section listing “risk factors,” Uber outlines its many competitors, including “public transportation, which typically provides the lowest-cost transportation option in many cities.”

The language was a shift from how Uber had talked publicly for years about being a complement to public transit. After an uproar among transit advocates, Uber updated its filing to largely eliminate references to competing with public transportation.

For now, Uber is taking its first foray into public transportation slowly, one city at a time. Earlier this week, the company added real-time subway and bus schedules, time and cost comparisons, and point-to-point directions for customers in London. A ticket-purchasing option is expected to launch in the weeks to come.