What would be "old time" curves in N scale?

[OldEastRR]

Granted that our curves on layouts  are way too sharp to look realistic but is it possible to have visible differences in track curves that were laid in two different eras? I have a downgraded mainline running through a town, which (as my history goes) was laid in the 1870s or '80s. It had to squeeze through buildings already there, and the town grew up close to the tracks. Obviously bigger and heavier locos and rolling stock evolved but the railroad couldn't put in wider curves without buying up a lot of expensive city property. Eventually a new main was built on the side of town with 1920s-era track standards. I'd like the "old" main to look, well, like an old 18th century ROW compared to the "new" one. But I don't want a cartoonishly sharp curve, besides I'll need to run locals switching on it. Any ideas?
BTW, the radius on the "new" main curve is something like seven or eight feet (or more), which might make this problem easier to solve.

[randgust]

It's usually more visible by the vertical roadbed height, rail size, and ballast (or lack of it).  You'll usually just see cinders and lighter rail.  Usually the 'new' route got ballast lifts and new ties, the old one didn't; rail upgrades and the old one didn't.   

Bridges are also a good indicator.     Street running was a lot more typical on original railroads if the town got there before they did, and pretty soon, something had to be done to get out of that mess.

Curves would be last on the list, actually.     

The award for the 'most miserable in-city curves that had to be bypassed' I've ever seen myself would be Lowell, MA, which dated back to the water and canal era, the railroads had to fight their way into the city via street ROW's.   The current MBTA/Guilford main line is a pretty stark contrast to the now-trolley track that wanders around through the city through relatively impossible sharp curves and bridges.   

Your original line very well may have been street running, too, which is an excellent reason to get out of Dodge and build a new high-speed bypass.   I think Utica, Schenectady, maybe Rochester had situations like that with the original NYC main lines and subsequent bypasses.   That's still being done today (Erie, PA didn't get NS out of 19th St. until the de-merger of Conrail and up onto the NYC right-of-way in 2001).   Another classic is the old Delaware & Ulster coming up out of Rondout and heading west through Kingston, just a horrible combination of steep grades and sharp curves and street running that was never upgraded until the day it was removed.  A small part remains as the New York Trolley Museum.

We had an 1880-built branch into our City by an NYC affiliate that got there late and resorted to street running over many blocks.   They made a 90-degree cut through the middle of a residential block right through some houses.  Always a 10mph curve and would just barely clear an 85-foot car.  Measures out at a 500' radius curve which is still wide by model standards - but compared to the PRR main line it looked like a horsecar track.

[Mark5]

These re-alignments were probably common over time. I can think of a few on the old N&W off hand.

[Ed Kapuscinski]

And don't forget that in many cases, the original alignments were retained and used as industrial leads.
Havre De Grace (https://goo.gl/maps/b3co8AoWNxG2), Newport PA (https://goo.gl/maps/ZtYUm6TbFKt), and Duncannon (https://goo.gl/maps/xAGaLHKdrew) all come to mind.

[randgust]

If you have a bypass, it may also be fully grade-separated.  That was the other bugaboo that railroads spent fortunes on and still do.  Your original street-level railroad may have been replaced with a parallel high viaduct with a multi-track main on it.   Look at Indianapolis - even today the route to Union Station is grade separated into downtown, and the 'belt line' struggles through at street level around wicked curves to get across the city.   Even today, they're trying - not real successfully - to figure out a way to get through Indianapolis and take the train traffic out of the middle of the city.

[OldEastRR]

And don't forget that in many cases, the original alignments were retained and used as industrial leads.
Havre De Grace (https://goo.gl/maps/b3co8AoWNxG2), Newport PA (https://goo.gl/maps/ZtYUm6TbFKt), and Duncannon (https://goo.gl/maps/xAGaLHKdrew) all come to mind.

That's the case on my layout. Town industries were served off the old main, so the track still in the city was retained. Locals use the interchange track where the two railroads crossed to get to the old main and switch  them. The rails of the old main (which was of a railroad bought by the newer railroad) outside of town are completely removed. This is what CSX did in Bloomington, IN after buying the Monon. Except CSX used the interchange with the ICG onto that RR to get from Bloomington to their mainline farther east.
Also, I have RDC service which terminates/originates on the stub end of old main in downtown.