we tend to frown upon people who disobey traffic rules
I've been taught we might "frown on" bad behaviours but needn't frown on people.
So for example I'm inclined to think, "that's bad driving", and not, "you're a bad person for driving that way".
I'd tend to frown on and stay clear of dangerous driving.
There's a saying, "Don't attribute to malice what you might attribute to incompetence"!
Double standards though: I do tend to attribute good (safe) driving to good will -- I've admired the way in which most drivers cooperate, coordinate with each other, by all obeying the same traffic laws.
Are breaking traffic rules deliberately
I believe intention matters, and than there is some variation due to local circumstance.
For example in France the speed limit is 130 km/hour on the highway, you may in practice be fined for driving at 134, most people don't exceed the speed limit, and neither do I.
Conversely in Ontario the official limit is (or was until recently) 100 km/hr, and everyone drives as if the real speed limit were 110 -- and in that situation, I figure that insisting on sticking to the letter of the law and driving at 95 would be less safe than driving at 110, like everyone else does, except in winter.
Is it a violation of Right Action?
Following the letter of the law, SN 45.8
And what is right action? Abstaining from taking life, abstaining from stealing, abstaining from unchastity. This is called right action.
These are three of the four Pārājika offences. So I think "Right Action" in that context is, "action which won't get you expelled from the community of monks".
And, strictly, "taking life" is a pārājika only if you're intending to kill. So, speeding, or failing to signal, resulting in an accident, presumably "doesn't count" unless you're doing it in order to kill (and not e.g. just out of carelessness).
But!! Some road accident can cause a lot grief.
is it a sign of a unwholesome or unskillful mindset from a Buddhist perspective
Again, I don't like to condemn others. I don't want to say, "if you do that then your mindset is unwholesome or unskillful". But I can tell you that when I drive or even ride a bike I'm conscious that it's potentially dangerous to other people on the road and that I can and must avoid those dangers by driving conscientiously -- and I think that's a virtue from a Buddhist perspective, mettā, ahimsa -- and may fit the definition of "skillful", in that its purpose includes "freedom from remorse".