Simulate a realistic multi-lane road junction with traffic lights and sensors in Gazebo Classic 11

I’m using Gazebo Classic (version 11) on Ubuntu 20.04, and I’m trying to create a realistic simulation of a multi-lane road junction (cross-intersection style), with the following elements:

What I’m trying to do:

  • A realistic 4-lane cross-intersection, with lane markings
  • Traffic lights placed at the junction (even if static for now)
  • Integration of sensors like a basic camera and ultrasonic sensors (mounted later)
  • I’d also like to use a custom STL model (for a road divider or barrier)

My main questions:

  1. How do I properly include an STL model in my world? I get crashes when using <include> with my STL-based model.
  2. Is there any tutorials to which would help code the models and worlds