What I did not know until I worked on the railways was that locomotives running "Light" (As in running without pulling anything) were restricted to a maximum speed of 40mph (I believe it was 40mph. Going by memory).
Now when it comes to our models and how they react, and where the weight is inside our models and how the couplings react and how we only effectively have locomotive breaking, and then go to how the real railway locos with their trains they pull react and how having breaks on the coaches or wagons they pull react, I can begin to understand why a solo locomotive on its own has a more restricted upper speed limit compared to when it is pulling a load.
It is interesting.
I only add this after seeing pictures of your locos running light.
I was also thinking they need head ad tail lamps.... And I have been toying with an idea of using magnets and steel so that the head and tail lights can easily be placed on a loco or an item of rolling stock and removed etc. May not be easy in the smaller scales. Is just a thought I have been thinking about.
Love the photographs.

Budget modelling in 0-16.5...