They have a knowledge of driving and navigation.
So what - what does that have to do with IP - you've not answered the question - what IP do they create at work? They don't AFAIK. So what conflict (other than driver hours) is there between their delivery driver job and their bus driver job - you've not answered/thought this through... if you had you'd see it is a silly comparison. There likely isn't any contractual issue preventing it aside form hours in the day...
If I create software. Then create a completely different piece of software. Using a different language for a different business area it's a bit much for some one to claim it's all the same IP.
What do you mean "its the same IP?"
This is all rather dependent on what you do in work, what your contract covers, whether the contract is reasonable and what your project is outside of work.
What if I'm a contractor working on one contract part of the week, and a different contract in a different business area the rest of the week. That is common enough.
What about it - the thread is about an employee. You might well have some NDA agreements to sign as a contractor but if you've been brought in part time for a specific task then you'd be silly to sign anything that prevents you from taking on other contracts in the rest of you time wouldn't you? Unless you were very well paid for it.