Yes, if the pause between levels is not a problem, level_load will save your global variables, but maybe you mean something slightly different...

Let's say you have a train that travels through one section of the town on a certain schedule. And if the player leaves the section with the train and comes back 5 minutes later, the train is still "on schedule": the train acts like it still exists even when the level is not loaded.

To do this, just make sure the train's position is based on global variables (like the total time passed). As long as the time variable is updated the train will be in the right place.

This could be complicated if you had a bunch of different things depending on each other (spies who travel by train, and agents that track spies and can modify the train schedule) but in theory, you can update these global variables even when the level isn't loaded.

You could use a starter function that always runs regardless of which level you're on.

Hope I'm helping and not confusing the issue.