Hola,
Since you mention "traffic" we must be referring to Managua, though Granada, Leon or Matagalpa can at times experience congestion .
The recurring theme here is an explosion of car and motorcycles for streets which were not originally conceived for even a fraction of this volume. All cities and municipalities worldwide today are grappling with this conundrum.
Four major roads regulate traffic in and out of Managua
Carreterra a Masaya: home to the latest economic expansion, should be avoided between 6:30 am and 9 am and later between 3:45 and 6:30 pm. The "Bypass", Carreterra Norte and Carreterra Sur...ditto.
The government has tried to alleviate things a bit with major construction work involving round-abouts and overpasses. The latest project underway near the US embassy is causing major deviations and delays at any time of the day pretty much.
It should be primordial to anyone looking for accommodation or work to take this information into account. Major quality of life issues are at stake here.
Personally, since I live in a rural setting some 40 klics out, traffic is not an issue. At least not one I need to contend with regularly, though I do schedule my day trips to Managua in such a way as to avoid being on the roads at these time.
In between cities, the roads are otherwise fine. Planning on visiting the Atlantic coast? I am sure you'd want to fly as there are no roads to speak off which would take you there.
Hope that helps,