When should I start building bigger roads?

[BurningSun]

Like the topic says..

I have 1,600 people in my city right now and I have all small roads except for a stretch of a medium road that connects my foresting industry to the rest of the city. At what point should I start building 6 lane roads and highways?

 

[Alex24]

If you follow the "hierarchy of roads" you should be getting to the point where you need them. Mostly for arterial and connector roads. The wiki article beneath got the theory and the guide on steam tells you how to do it in CSL.
> Wikipedia Article - https://en.wikipedia.org/wiki/Hierarchy_of_roads
> Popular Steam Guide - http://steamcommunity.com/sharedfiles/filedetails/?id=410236188

 

[Dell19]

In my current city (pop 115k) I've relied almost entirely on the smallest roads with a highway circling the city for long distance traffic. There are I think three places where I've used three lane roads just to increase the speed that vehicles can travel at.

The most important thing seems to be avoiding choke points where for instance you have two roads meeting where one runs north south and the other runs east west and lots of traffic is going in multiple directions. In some places to get around this I've elevated one road and then added off ramps so that only traffic that needs to switch from the N - S road to the E - W road actually has to wait.