Easy:
Take one (1) Hotrod F7 (previously supercharged to exceed said limit).
Couple to the front of said F7 one (1) freight car of your choice.
Speed up both F7 and car on one (1) sizeable loop of track.
Once said limit is surpassed, put said F7 into idle and decouple said freight car from said F7.
Congratulations! You now should have one (1) freight car travelling in excess of said limit and one (1) supercharged Hotrod F7 decellerating behind said freight car. Now watch as said freight car begins to outrun said F7, or flip a conveniently placed switch/junction along the route to double the excitement!