That would be unsafe in many situations. If the flow of traffic is substantially above the speed limit--which it often is--being unable to match it increases the risk of accident. This is known as the Solomon curve [1].
With the logic presented in the theoretical foundation section, it seems that the safer move would actually be slow down and match the speed of all the trucks and other large vehicles... which won't happen.
Matching speed sounds great, except there are always people willing to go faster and faster. In my state they raised the speed limit from 70 to 75, it just means more people are going 85-90. How is that safer?
However, you individually going 70-75 when everyone else is going 85-90 is less safe than you going 85-90 like everyone else in the exact same situation.
>there are always people willing to go faster and faster
That’s why no one says “go as fast as the fastest vehicle you see”, it is “go with the general speed of traffic”. That’s an exercise for human judgement to figure that one out, which is why imo it isn’t a smart idea to have the car automatically lock you out of overriding the speed limit.
And yet the roads are full of vehicles literally incapable of going 85. Many trucks cannot do more than 69mph.
(Trivial if the self driving tech works at all....)
There's just too much shit that can't be "seen" with a camera/sensor in conjested traffic. Having a swarm of vehicles all gathering/sharing data is one of the only true ways forward IMO.