And in reply, Tony wrote "that from the 1890s onward, there were many incidents around North America of horrific accidents with wood passenger cars in wrecks, and the resultant fires and loss of life", which I support as gospel truth.
And if anyone doubts it, imagine seeing accounts with images such as these:
http://www.celebrateboston.com/disasters/bussey-bridge-wreck.htm
https://raycityhistory.wordpress.com/2010/12/22/railroad-horror-1888-train-wreck-kills-john-t-ray-and-30-odd-others/

The reasons why have to do with the advent of signaling in this same time frame. And, moderators, a bit of leeway here and I'll bring it back home. 

    "Signaling" as claimed by a large number of railroads during the time frame mentioned was mostly "block signaling" which meant an operator in a structure with train order boards and a telegraph set. Not too far removed from the "Captain, may I?" some of us played in the school lot on recess. I recall reading a story in an old (very old) railroad (pulp paper) magazine, where a self-professed Boomer, when employed in such service, relayed in print - rather proudly it seems in hindsight - that if you needed a nap, you would place a car seal between rail ends and if  woken by the dispatcher enquiring if a train came by, you looked out to see if the car seal was bent and which way. Imagine being on a passenger train in the care of such a person.  Human nature being what it was, wrecks as Tony relayed did happen. 
      The then President of my studied railroad when taking a trip over the 1100 miles or so of now "fully signaled mainline" wrote to his board that he was deeply dismayed to find that the signaling system that he had been promised (and paid for) was now in the hands of people who primary duty it was, would be to stay alert. 
     
     That lead to congress being called to act. In response to the events that Tony touched on, Congress looked to take action however the railroads first obscured the argument by pointing out the current state of flux in the then signaling options available. Notably, New York Central was an early embracer of what we think of currently as signaling. Pennsy and quite a few other railroads simply had the density to keep the tower operators they employed busy and so at least on the mainline, it was safe enough.

      NYC then embraced the "Great Steel Fleet" slogan which they advertised heavily with. 

      NP used the attached ad to promote safety. Note how the half tone semaphore signals actually occupy quite a bit of the ad. That was even though at the 1912 time of the ad, much of the railroad mainline still existed sans Automatic Block Signaling. The CMStP&P at this same time was promoting color light signals in their ads. 

One of the companies that sold these signals promoted "a system that never sleeps".

     Meanwhile on my railroad, an articulated had briskly bumped the end of I believe an SP&S passenger train at Cheney, WA. (# 6?) Now that got everyone's attention on the corporate board. And set in motion the later semaphore signaling that was an NP trademark. (Which protected the trains that haul our steam freight cars.)    

      However, as Dennis relayed, change to protecting the employees came slower than protecting its own image with the public. This sentiment lasted well into the 1920's and saw the Automatic Train Control and Automatic Train Stop systems of that time being mandated. As well as other provisions like a 12-hour workday. The Adamson Act and then there are others.

The boober cabooses are only a small part of this. 

      Yes, Charlie, the Hill lines mechanical departments often worked together. As did many railroads. Many of us here when researching our railroads mechanical files, and in those files researching the records of the Steam Freight Cars found here, find letters between mechanical officers of other railroads.  
                                                                                                                                                                                                                      James Dick      Roseville, MN                                        

      BTW, plug that $37,500 number from the AFE images supplied by Hudson into a CPI adjuster and you get well over a million dollars in current terms.