I have just bought a new plug in Prius and was shocked by just how awful the RSA system is. Road Sign Assist (RSA) system is dangerously inaccurate. It responds to images from the front camera and is supposed to ‘read’ road signs and indicate the current speed limit and allow alarms to be set if it is exceeded. However, it shows no speed limit at all about half the time. Even when it does show a speed limit it is often incorrect. It frequently misses the change between one speed limit and the next. It does not generally respond at all to the end of speed limit signs. On occasion it responds to signs in parallel roads, indicating for example a 30mph limit while driving on a dual carriageway with a 70mph limit. It has no knowledge of the 60mph speed limit on unsigned single carriageway roads or the 70mph limit on unsigned dual carriageways and motorways. It absolutely cannot be relied on. The result is that the indicated speed limit – and any warning that has been set – may result in a driver driving dangerously slowly or illegally fast. I might also add that it has never shown any other road sign at all which could also be dangerous. But the worst of it is that there is another more accurate speed limit indicator built into the navigation system. That uses the GPS position of the vehicle to show the current limit that applies to the road where the car is located. I have had experience of that system for seven years on the Prius Which I part-exchanged for my new vehicle. It works well – I would say it is almost never wrong. However on the newest models this accurate system is disabled if RSA is fitted. It is still visible on the settings for the navigation system but is greyed out and cannot be accessed, though clearly it is still there. Turning off the RSA does not re-enable this speed limit indicator. So the driver has no choice as to which system – or both – to use. This is not a fun gizmo, it is a crucial piece of safety equipment so I am shocked that Toyota has disabled the accurate system and replaced it with the very inaccurate RSA system. I am in the UK and in my view this feature of the vehicle is not fit for its particular purpose under s.10 of the Consumer Rights Act 2015. I have asked my dealer to sort this out and find a way to allow me to switch on the accurate Nav system speed limit indicator. I was also shocked looking at this chat that similar feedback about RSA has been given for at least three years. Maybe if I return the car and demand my money back the problem will be taken seriously!!