Actually, I have worked on the reversionary issue as part of my job. It's not always cut and dried. It all depends on what the abutting land owner's quality of title is and the particulars of applicable state law. Given the right wording in a deed, an abutting land owner can have a sustainable claim of reversion after a rail line has been formerly/legally abandoned. When the railroad was built is not a factor.

Also, how and who granted the railroad interest can be determinative. A while back there was a case that made it all the way to the SCOTUS. It involved a grant of land to a railroad under a specific federal statute and a trail. The rail line was eventually abandoned and a trail created. One land owner through whose property a portion of the trail passed argued that, under the land grant statute, the grant to the railroad consisted of an easement only and that the easement was extinguished when the line was legally abandoned. The government argued that it created a fee title and thus the landowner had no claim to the property that had hosted the former rail line. The SCOTUS, in what I believe was a unanimous decision, held in favor of the landowner.

Then you have the issue of what's known as "rail banking." Claims of adverse possession can also come into play. The typical scenario in the latter is that a landowner who had granted a railroad fee title to a strip of land that abutted (or ran through) his property makes use of the property (classic example is the construction of a shed or other outbuilding) after abandonment of the rail line for whatever the particular state's prescribed period is (often 22 or 22 years) and claims ownership as a result.

There are even seemingly absurd examples running against landowners: Predecessor in title grants a railroad a strip of land through the middle of his square parcel "for use as a railroad, and for no other purpose." Railroad is there for a lonnnnnnnnnnnnnng time. The line is eventually abandoned. Current owner argue that the railroad no longer has a claim to the strip due to abandonment. Seems credible. Not in Michigan, as its courts have ruled that, without any express revisionary language in the original deed to the railroad, the grant to the railroad created fee title notwithstanding the deed language saying that the grant was only for railroad purposes.