Uber’s self-driving cars are back on public roads in Pittsburgh this week, four months after a fatal crash prompted the company to shut down its testing program in North America. For now, the vehicles will not be driven in autonomous mode, but instead will be manually operated by human safety drivers while Uber continues its “top-to-bottom” review of its self-driving program.

The company’s fleet of Volvo XC90 SUVs have been gathering dust since March, when a self-driving Uber car struck and killed 49-year-old Elaine Herzberg while she was crossing the street in Tempe, Arizona. Uber immediately grounded its fleet as federal investigators began to probe what went wrong. The governor of Arizona barred the company from further testing in his state, and Uber subsequently laid off hundreds of safety drivers in Arizona and Pittsburgh.

Don’t call it a comeback

But in recent weeks, Uber has been positioning itself for a comeback — albeit a much more scaled back and overtly cautious one. So while its autonomous cars will be hitting public streets again, they will be driven manually by the company’s newly branded “mission specialists” for the purposes of data collection and map updates, said Eric Meyhofer, head of Uber’s Advanced Technologies Group, in a Medium post Tuesday.

Pittsburgh officials will be watching Uber like a hawk as it gradually restarts its program. “Uber has kept Mayor Peduto updated on their plans and he appreciates the company restarting operations in manual mode to be extra careful on Pittsburgh streets,” a spokesperson for Pittsburgh Mayor Bill Peduto said in an email. “He and fellow administration officials will continue to work with the company on safety initiatives.”

The cars will also feature a few new bells and whistles, including an active driver monitoring system that keeps tabs on the safety driver while they are keeping tabs on the car. This includes a driver-facing camera that issues audible warnings if it detects “inattentive behavior.” Uber says it will be using an “off-the-shelf” system to monitor its drivers, but declined to name the vendor.

Uber is reactivating emergency braking in its fleet of Volvo SUVs

Driver monitoring is increasingly becoming a crucial factor for advanced driver assist systems and self-driving ones alike. Cadillac uses infrared cameras to track drivers’ eye movements as they use its semi-autonomous, hands-free Super Cruise feature. And Tesla reportedly rejected more rigorous driver monitoring to improve its Autopilot system, but is now rumored to be rethinking that decision. By adding a driver monitoring system, Uber is signaling that the fatal incident in Arizona, in which police say the safety driver was watching The Voice on her phone at the time of the crash, won’t happen again.

Another major change by Uber is to re-enable Volvo’s factory settings for automatic emergency braking and collision avoidance in its fleet of self-driving cars. That system had been disabled at the time of the crash, even though the vehicle’s built-in radar observed the victim six seconds before impact and identified a need to brake. Uber reportedly deactivated the system to avoid a less-smooth driving experience for its safety operators. There has been plenty of speculation that had Volvo’s driver assist systems been active at the time of the crash, then Herzberg would still be alive.

Uber was only using one safety driver per vehicle at the time of the crash. Now, there will be two mission specialists, Meyhofer says: one behind the wheel to monitor vehicle operations, and the other in the passenger seat to record significant events. These specialists will be subject to Uber’s newly “rigorous” training program, which includes defensive driving techniques and “improved test track situational awareness drills.” Uber is also working to minimize in-cabin distractions by modifying the touchscreen in the center console.

An emphasis on simulation

In the aftermath of the crash, Uber was criticized for under-investing in its simulation program. This stood in contrast to competitors like Waymo, which often touts the billions of miles driven by its virtual self-driving cars in its simulated “Carcraft” program as an important bulwark to its real-world testing. Uber reportedly de-emphasized that kind of testing, but is now highlighting its simulation program as a critical link in the overall self-driving puzzle.

“Manual driving allows us to see in real-time different scenarios that our self-driving cars will encounter on the road,” Meyhofer writes. “We then recreate those scenarios in a virtual world, and on the test track, to improve overall system performance under similar conditions.” No word, though, on the breadth of Uber’s simulation program.

The National Traffic Safety Board is still investigating the fatal crash in Arizona. The agency released a preliminary report in May that concluded that Uber’s vehicle failed to brake in the crucial seconds before the crash. A final report, in which the agency may assign blame and make recommendations, is expected early next year.