How to generate simulated car movements in Gazebo

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I originally posted this question on ROS web site and I am redirected to here.

I would like to be able to automatically run a model car, without manual intervention, through a specific location on the road. The model car's movement could be based on Gazebo world configuration (so the car query Gazebo for the road and actually follow the road, etc) instead of visual/lidar sensor data. I would also like to introduce some randomness so that the car moves somewhat differently each time. I wonder if there are any existing open source tools to do that or if there are sample codes that I could start with.