Present Perfect tense in combination with 'for/in/since'

I'm currently having a discussion with a friend regarding the usage of a present perfect tense in combination with for/in/since etc.

It revolves around this sentence:

Traffic has been a big problem in The Netherlands for the past few years.

To my understanding with this sentence you say traffic was a problem till now, because with 'for the past few years' you indicate that the problem is solved recently.

But he says the meaning of the sentence here is: 'traffic was and is still a problem'.

I believe this is incorrect, and if he wants to indicate that traffic was and still is a problem he would need to formulate the sentence as followed: 'Traffic has been a big problem in The Netherlands in the past few years.'

*Originally I wanted to use 'since the past few years' but according to this topic that is incorrect in English grammar.

Regardless, I hope you can shed some light if I'm wrong and hopefully also why I'm wrong so I can learn.

I think either preposition is compatible with the meaning that traffic is no longer a big problem.

a. Traffic has been a big problem in The Netherlands for/in the past few years--until now. Now, a new highway is opened.

But maybe you might want to use for instead of in if you mean that traffic is still a big problem, because somehow c. sounds awkward.

b. Traffic has been a big problem in The Netherlands for the past few years now.

c. ?Traffic has been a big problem in The Netherlands in the past few years now.

It doesn't matter in this case -- your friend is right. Now I'll explain, and give you some general guidance. The choice of tense trumps the preposition. The tense is the core of the sentence. Prepositions are hard to get exactly right, and sometimes there isn't an exactly right. You can flub your prepositions more than your tenses. I know this because when my German spouse gets a tense wrong, it's much more annoying than a slightly imperfect preposition.