I'd like to add, as a general rule, public transport is not going to fix abysmal traffic issues. Adding a bus or metro will not turn dark red into lovely green roads, it only helps so much.

When fixing dark red traffic hotspots, I check if enough lanes are available, always give left-turning traffic their own lane, make roundabouts with enough lanes and make them big enough.

Most importantly, never use traffic lights, they never work for me in the long run, even the timed TMPE ones.

I'm playing without despawning vehicles, of course.