Where I live, it’s all planned out in CAD, and then the inner concrete curb is calculated and broken up into sections, according to the plan.

Then the intersection being replaced (because that’s almost always the case) is dug up in the center and the concrete forms put in place and the center backfilled with gravel and dirt.

After the concrete has set, the asphalt machines re-level and pave the surrounding area. After this, brick is often added inside the concrete to provide an extra driving surface for large vehicles. Then plants or statues are added to the centre.

After all this, the lines and markings go on, and they’re just offset from the concrete curb, so nothing fancy needs to be done; the paint truck just has a little arm that stays over the concrete.