Without any pertinent knowledge of the problem, I would say that the same traffic volume can flow though a highway in two different conditions (low-density & high-velocity or high-density & low-velocity). A shock arises when traffic abruptly jumps from the first to the second condition

Dear Guido Colasurdo

Thank you for your assistance. Colud you please propose an interesting subject about shockwaves on highways related to your field.

Best regards

Sorry, I do not deal with similar topics. In the past, when I worked on the integration of hyperbolic flow equations, I was aware that similar equations had been used to analyze highway traffic and propagation of disturbs upstream. You should be able to find some papers in literature