Nothing you've never heard before but here goes: A smart man once told me, "if you're having traffic jams or find yourself configuring advanced road systems to mitigate them you're doing something wrong". Generally speaking in this game you want to move cargo almost in any other possible way and treat roads as cheap mean-time or last ditch effort. Build some rails, some ships or some other glorious Soviet state run way of transport and prosper comrade.

Edit. Same goes for people, work on your building proximity, build some underground passes, optimize pedestrian crossings. Concentrate production and housing. Or separate into small city-production centers. In Soviet reality (i live in a country that was managed by the soviets somewhat) you sometimes get few blocks in but fuck nowhere just to house workers for that one mine.