Four months after a fatal crash forced Uber to halt testing of its self-driving cars nationwide, the company announced Tuesday that it is resuming testing on Pittsburgh streets. But the announcement comes with an important caveat: initially, the cars will only be driven in "manual mode" with human drivers—not Uber's software—controlling them.

"We're starting with cars in manual mode, with a Mission Specialist sitting behind the wheel and manually controlling the vehicle at all times," writes Eric Meyhofer, the leader of Uber's self-driving car program. "While we are eager to resume testing of our self-driving system, we see manual driving as an important first step."

Driving around in manual mode won't allow Uber to directly test its self-driving car software. But it will allow the company to gather data that will improve Uber's maps and simulation software. It's also a way for Uber to test the political waters in Pittsburgh before diving in headfirst. Uber's plan to resume testing in Pittsburgh initially met with criticism from Mayor Bill Peduto.

Uber says it's taking precautions to make sure its new testing regime is much safer than the one that killed pedestrian Elaine Herzberg in Tempe, Arizona, earlier this year.

There will now be two people—known as "mission specialists"—in each car. One of them will be responsible for driving the vehicle (or, later, monitoring the vehicle as it drives itself). The other person will "document notable events"—providing data and feedback that Uber engineers will later be able to use to improve the cars' performance.

At the time of the March crash, Uber was asking a single driver to perform both tasks simultaneously—an arrangement that created an obvious risk of driver distraction. Now Uber says in-car systems have been redesigned to minimize driver distraction, and the company has given safety drivers additional training.

Perhaps most importantly, Uber says it will no longer disable the collision avoidance systems on its Volvo vehicles. At the time of the March crash, Uber had reportedly disabled this software, relying on the human driver to brake if the car was on a collision course.