In the "highway-v0" scene, how can I add obstacles at a specific location?

[1cai2]

1.In the "highway-v0" scene, I want to add an obstacle at the specified coordinates, and this obstacle can appear in the observation space of ego-vehicle and does not collide with surrounding vehicles. How to realize this function?
2.In the "highway-v0" scene,the distance range of surrounding vehicles observed by ego-vehicle?
3.How can I get an observation of the nearest car in front of ego-vehicle in the current lane?