Truck and Trailer driving performance

Hi all,
I´m doing a research project for an economic class in a german university and looking for support. Among other things we have to figure out a couple questions considering the driving performance in several countries…
If you guys could help me out here, this would be perfect! Of course it´s okay to quote a range for the asked numbers.
1) How many kilometers do you drive your truck per annum?
2) Is your trailer only driven by your truck or also by other truckers?
Considering 1) and 2), is your trailer driven more than your truck?
3) How many kilometers is your trailer driven per annum?
4) How often do you do empty trips / carry an empty Trailer? (percentage)
5) Approximately, how long is your trailer in use? (years)
Feel free to answer just a few questions, if you are not able to point out some facts. However, if it´s possible just give me a wider range…better something than nothing
Thanks in advance! You would help me a lot with this!
Cheers, Mike