All old hog heads know those were the lines to admit the Steam Bugs. Steam bugs added about 1000 lbs of tractive effort when you let them loose in the pistons(think about thousands of angry killer bees times 10). They were kept in what looked like an air tank. If the engineer was having a little difficult time moving a train over the road he could turn on one of the steam bug valves and get-er-done PDQ. If he turned on both the effect was somewhat like the special wood used on Sierra #3 in Back to the Future III. These lines became obsolete when the last population of steam bugs went extinct around 1938 in the distant regions of Tanzania. Attempts by Baldwin and Alco to captive breed them were to no avail. The cause of their extinct was said to be preliminary global warming. The decline in the population of steam bugs led to the development of the high pressure superpower locomotives of the late 1920's and 1930's. Sadly, no one ever took a photo of one as they attacked any camera looking device with extreme prejudice...