Cruise Control problems of the 2017 Toyota Prius

In moderate to heavy rain with the Toyota dynamic cruise control engaged on the highway between 55 and 70 mph, the Prius has dangerously accelerated itself towards a car immediately in front of my car and would have created a front-to-rear collision if I was not extremely vigilant and manually braked and canceled the adaptive cruise system within 10-20 feet of the car in front of me. The system seems to operate blindly in moderate to heavy rain and will accelerate to user-set speed even when a car is traveling slower immediately in front of my vehicle. I strongly suspect the pre-collision braking is failing at the same time as the dynamic cruise (in rain) since it relies on the same components. The Prius prime needs to be reprogrammed to not allow dynamic cruise engagement in moderate to heavy rain. This is a very dangerous situation because driver visibility is already impaired under these conditions. If this did not occur multiple times, I would not have believed it was actually happening. The Prius manual says that rain can cause the system to not behave as intended; however, in that case it needs to be automatically disabled so it does not create a very false sense of security. This is going to cost lives if it's not reprogrammed. I would be surprised if this was the only Toyota that exhibits this dangerous behavior. I strongly believe that lives can be saved with a simple reprogram of the system to not allow operation under conditions that can create unintended acceleration into a slower moving vehicle. Toyota should save themselves millions in potential liability and take this suggestion seriously.

While driving on interstate highway in heavy traffic using cruise control my car suddenly accelerated quickly. Weather was alight rain. It was like the radar for the cruise control shut off or stopped being processed.

The adaptive cruise control in this vehicle has several operational issues (programming bugs or defects) which are potentially extremely hazardous. Perhaps the most potentially dangerous behavior of the system is as follows: - when using adaptive cruise control, the system automatically accelerates and applies braking force to stay a set distance (one of three distances) from the nearest preceding vehicle. - when the nearest preceding vehicle changes lanes, the system can become confused, display "no preceding vehicle" and disengage. - this behavior can be dangerous or life-threatening in some cases, which I've experienced several times: what happened: - highway driving at 65mph, using adaptive cruise control and following another vehicle. - we approach an area of congestion or stopped vehicles (a traffic jam). - the preceding vehicle begins quick deceleration in order to avoid rear-ending the vehicle in front of it. - my adaptive cruise control also applies strong braking to maintain its programmed distance - the preceding vehicle changes lanes out of my lane - my adaptive cruise control displays "no preceding vehicle" and disengages, which means that it stops braking - my car is now flying into the vehicle in front of me, giving me only a moment to react and apply braking. Instead of disengaging during braking, the adaptive cruise control should continue braking down to a speed of 25mph, which is the maximum speed that Toyota's safety stop operates at to bring a car to a complete stop. The current behavior of the system has led to several near accidents in my highway driving, and is undoubtedly a danger to anyone else who uses a Toyota adaptive cruise control of this model on the highway. I reported this issue to Toyota last year and they seem uninterested in fixing it, refusing even to convey my report to their developers in japan.