Roads and railroads are NOT equivalent, neither in the Industrial Era when railroads were first built, nor today. Quick Comparison: one train on the average American railroad is 100 50 ton freight cars, which can be moved at up to 100 kph for 24 hours continuously by a crew totaling about 9 men (in 3 shifts). To move the same amount of goods by modern highway in '18-wheel' trucks would require about 75 - 100 trucks and a total crew of that many drivers and could only move (legally) for about 10 hours a day. If you have to move people or goods in quantity long distances you do it by water or rail. Period.
And, of course, in the 19th century the trains only carried about 1500 - 2000 tons each at 50 kph, but animal-drawn transport (the only land alternative) could carry no more than 5 - 10 tons/vehicle at about 4 - 5 kph. The advent of the railroad was the first time in history that a human being could travel faster than 30 miles in an hour anywhere on earth, unless they were blown by a hurricane or falling off a cliff. The railroad changed virtually everything about people's lives, expectations, and quality of life. It also made it possible, for the first time in history, to feed a city that wasn't on a coast or river from more than 50 miles away. If they ever represented that correctly in the game, then quite simply all your 'city radius' calculations would go right out the window as soon as you had a railroad connection.
Leaving railroads out of the game and expecting them to be represented by roads of any kind makes this a fantasy game, and a poorly designed one at that.