How to increase density of vehicles in an environment?

I’ve made an environment like highway-v0, which vehicle’s action space is continuous, and it tries to reach a goal while avoiding a crash. Here’s an episode of a learned agent with the SAC model.

As the density of vehicles in the environment is low, the agent has not a difficult job avoiding them(and it seems it is the IDM vehicle which is avoiding the agent?). I tried to make it harder for the agent by increasing the number of vehicles, but the density of vehicles around remains the same. How can I make it harder, like the animation in the README file from the highway-v0 environment?

[eleurent]

I’ve seen this behaviour before: once it sees an obstacle, the IDM model starts braking, and this causes the MOBIL model to consider a lane change.

1. If a lane change is possible (it would not cut-in in front of another vehicle), a lane change is triggered and the vehicle avoids the obstacle/landmark
2. Else (would cut-in), the vehicle cannot change lane and can only brake and stop. Once it is stopped at the obstacle, the MOBIL now recommends a lane change, but IDM still outputs an acceleration of 0 (since the obstacle is close), so the vehicle is stuck.

[eleurent]

Nice environment, by the way! 👍