Crashes involving inattentive drivers relying too heavily on Tesla's semi-autonomous Autopilot system are nothing new. Sadly, some have been fatal. This one, however, is more unusual and embarrassing than most. In Arizona, the driver of a Tesla Model S clearly wasn't paying attention.

With Autopilot activated, the electric sedan smashed into the back of a police SUV that was parked on the side of the road. In a domino effect, the impact caused the police SUV to crash into the back of an ambulance in front of it, reducing all three vehicles to a mangled mess.

Ironically, the police SUV and ambulance were attending to an earlier accident before the Autopilot-enabled Model S slammed into them. The accident happened on Interstate 10 eastbound near Benson, Arizona. In response to the accident, the Arizona DPS wrote a very clear message on Twitter: "Reminder: Please #SlowDown & #MoveOver when you see flashing lights & vehicles stopped on the side of the road!"

Luckily, the officer wasn't inside the police SUV when the crash happened and was uninjured. Paramedics inside the ambulance weren't injured during the crash either. The same can't be said for the driver, however, who is being treated in hospital for serious, but not life-threatening injuries.

As for why the driver's reaction times weren't fast enough to avoid the collision? The 23-year old male driver is being investigated for driving under the influence.

Tesla's Autopilot system is advanced, but it's not fully autonomous, meaning drivers are required to keep their hands on the wheel to intervene if necessary and pay attention to the road ahead. Clearly, many drivers are still over-reliant on Tesla's Autopilot system. One organization that believes Tesla's Autopilot system is misleading is the Munich Association. After Tesla was taken to court in Munich last month, a new ruling has banned advertisements for Tesla's Autopilot system in Germany over fears they mislead drivers into thinking they can rely on the assist without any intervention.