This is how the session was setup by the author. However... You can do two things.
1) Create your own session and run things how you like it.
or
2) Modify the session on the fly.
You see you have the Platinum edition. Platinum like Plus allows you to switch between Driver and Surveyor on the fly. You may receive a warning about losing activity points. If this is a big concern for you, then don't do this, but by the sounds of it, it's not. Anyway, to do this you click on the wrench icon and go to Surveyor where you can modify things as you see fit. When all finished in Surveyor, click on the wrench and you can switch to Driver again. When you switch between the modes, the game will start up again paused in Driver, and as always in Surveyor. So keep that in mind when you go back to driving. Some people have asked why are things paused. We discovered during testing that it was a bit "edgy" to out wit the AI drivers when trying to fix things while they were getting in the way. By pausing the action, we can jump in and do what we have to then start things up again.
Now should you want to save things, you'll do so and the changes will be saved under your Username and ID with all the action set up just as it is when you made the changes.