Grids don't help much. Take a look at Google Maps' traffic report of Los Angeles' perfect grid layout during rush hour: the entire grid is usually solid red, almost every day.
Like most other plans for ameliorating heavy traffic, it is somewhat effective for a short time, but it soon just causes that many more cars to try to drive through the area.
it actually works great with less people. the problem is hitting that threshold requires regulation, which is a political impossibility except for special events.
So less people driving leads to less traffic, what a surprise.
I think that LA takes pride in its traffic, like some kind of shared struggle.
It is the only city I have lived in that has an implied 30 minute allowance for traffic delays. Everyone understands and you can use the excuse anytime or day of the week.
You think it would be better if it were a dendritic system? It's hard to believe that e.g., randomly walling off half of those grid links would make traffic better.
I doubt it. It won't fix the fundamental problem of moving lots of people to where they want to go in the city. You can only do that by making the area undesirable to go to for whatever reason (probably not a good option), or by providing some alternate means of getting places. Unfortunately, due to the sprawling way LA is laid out, all of the other options are even worse than driving there.
In a dense area like Manhattan, transport is not so bad because walking, cabs, or the subway are all viable alternatives in many cases.
In a lower density sprawl area like Los Angeles, cabs are prohibitively expensive for most trips, the subway usually doesn't go anywhere near where you are or where you want to go, the buses are stuck in traffic like any other vehicle, and walking is dangerous (due to the lack of pedestrian-friendly sidewalks in many areas) and would take many hours for each trip.
I think the best way to fix LA traffic would be to greatly increase the density and start building upwards so that walking and public transport become viable options for many more cases, but that seems very unlikely to happen anytime soon. It'd take decades to do anyway. So for now, it looks like LA is just stuck with its insane traffic status quo.
Like most other plans for ameliorating heavy traffic, it is somewhat effective for a short time, but it soon just causes that many more cars to try to drive through the area.