The commas around arguably set it off because it is a nonessential adverb and serves to qualify the statement without being integral to its meaning.
The last comma is there not because it precedes an independent clause, as another answer states, but because the phrase beginning with in addition to is a long prepositional phrase and should be followed by a comma when placed at the start of a clause. There are two clauses in this sentence: It . . . impact (independent) and because . . . system (dependent). Both arguably and this prepositional phrase are interruptions between the subordinating conjunction because and the rest of the dependent clause. Prepositional phrases considered “long” (which is ambiguous but typically regarded as over four words or so) are followed by a comma when they precede the rest of a clause to help parse the sentence.
If you were to remove arguably, whether or not a comma should still be placed after because depends on the intended meaning. If the prepositional phrase is regarded as nonessential, the comma would be appropriate. However, I would argue that the way this sentence is structured makes the phrase essential—removing it results in It has a wider-reaching impact because it also benefits the public commuting system, which to me seems incorrect because also is now out of place here since nothing else has been stated as an impact. Thus, it would make more sense to regard it as essential and not to have a comma.