I'm trying to stimulate a bit of interest in this thread again, particularly now that absolute power is out.

From this forum http://www.the-nextlevel.com/tropico/caf...ic=11301.0

Quote by loverevolutionary - "I just figured out why the Taxi Tycoon Guide is wrong, and why his experiment didn't work: drop-offs. When a Tropican wants to visit a building, his car stops outside that building to let him off, holding up traffic. With only loops and no side roads, this will be a major problem. As intersections don't slow traffic down realistically, it may be better to have more intersections to side roads that have high traffic buildings fronting them. Also, without a nearby garage, the car will have to make a long trip to one, creating even more traffic problems."

This is also something I have observed.
One point not brought up by FritoPatata is the fact that cars don't just disappear they have to go to a garage after dropping off.
I haven't tested the loverevolutionary idea of side roads yet, does anyone else tested this?

I my last game I had a single route from my mining area to the dock with housing and services on a side loop on the way. Where houses were close to the main road junction, traffic slowdown was increased by cars dropping off at houses (which then continue on to another garage).

Hypothesis:
To effectively manage a large island traffic must free flowing. On a long road with no intersection and no drop offs cars move quickly and efficiently. This is want we want to achieve.
Congestion is caused by two things;
1) Cars trying to turn across traffic into and out of intersections (Cars turning right into an intersection do not really slow down that much and cause much congestion?)
2) Cars stopping for drop offs cause all traffic behind them to stop.