The development of automated vehicles is ongoing at a breakneck pace. The human factors challenges of designing safe automation systems are critical as the first several generations of automated vehicles are expected to be semi- autonomous, requiring frequent transfers of control between the driver and vehicle. A driving simulator study was performed with 20 participants to study transfers of control in highly automated vehicles. We observed driver performance and measured comfort as an indicator of the development of trust in the system. One study drive used a more capable automation system that was able to respond to most events by slowing or changing lanes on its own. The other study drive used a less capable automation system that issued takeover requests (TORs) in all cases. Thus there was a change in reliability over the course of the study drives;​ some participants experienced the more-capable system first followed by the less-capable system, and others had the opposite experience. We observed three types of comfort profiles over the course of the drives. Some drivers started out very comfortable, while others took a long time to become comfortable. Takeovers were split into physical takeover, visual attention, and vehicle stabilization. Response time and performance measures showed that there was a 15- to 25-second period between the physical takeover and a return to normal driving performance. This confirms some observations in previous studies on transfer of control.