Scientist

This may look like a normal class 120, only in modern livery and with advertisement. That is, however, not the case. This engine used to be called 120 153 and got sold to DB Systemtechnik (System Technology) and is now called 120 501. Together with 120 502 (the former 120 160), it's job is to test new components, haul track measurement devices, work when testing new locomotives and similar. Just exactly what it is doing here pushing an, as far as I can tell, completely normal InterCity out of Cologne main station I don't know, but I guess there is some explanation. Maybe it's testing out how some modification works in normal duty. Maybe DB Fernverkehr (long haul) borrowed it because they're short a few locomotives. This has happened before so that's most likely. However it is a pretty boring explanation for such a rare locomotive, so I prefer the testing new stuff one.

This engine is, by the way, not to be confused with the prototype 120s, which did the very same job under the name class 752 years ago. Those were retired, and the new 120.5s are normal production 120s reused for this purpose.