The Big Boy locomotive with its tender weighed about 604 tons and measured more than 132 feet in length. I believe this was the heaviest setup ever used in North America. It had a maximum power capacity of more than 6,000 horsepower and could haul a 3,600-ton train unassisted up the Wasatch Mountain grade.
While I am not at all a fan of Greta, and enjoyed watching Sky News respond to her little tantrum, I am sure glad freight is moved by somewhat cleaner locomotives now. Coal and later fuel oil, were cheap and readily available 70 years ago and made sense then, but I can't imagine what the air would look like along a major rail artery with the number of trains and the amount of freight that is hauled today.
That might be true where you are but on the BNSF near where I lived there are more and longer trains than there were before. Oil trains, coal trains, container trains, mixed freight all more often and longer. It's hard to believe that a population that was half of what it is now, and a population that was way less materialistic required more freight trains than are operating now despite the exponential growth in trucking.
There is less mileage of rails but more tonnage on heavier lines. I resided in a little town that had a full train* every 20 minutes. No cycling on that grade.....
Actually as I thought about it, it is true of where I lived too at least in miles of track, but all the rails that are now trails were spur lines built for freight and passenger service into the river valleys of the Cascades. They hauled lumber, limestone, coal, cement, logs which in some cases are hauled by truck but in many cases the mills and mines have shut down and the need just isn't there. Others were lines abandoned because of redundancy after rail mergers. The main lines are busier than ever and I would not want to live along a modern east-west rail corridor if all trains were powered by coal like in the above coal train video.