“She’s so ugly she’d make a freight train take a dirt road”

“She’s so ugly she’d make a freight train take a dirt road” (the expression has also been used to describe an ugly man) means someone who is so very ugly that, metaphorically, a train decides to jump the track. The expression has been popular in many southern states and does not have a known author.
 
“She’s so ugly, she would make a freight train take a dirt road” was cited in a 1972 article about Virginia sayings. “She’d make a freight train take a dirt road on a muddy night” was cited in 1980.
 
 
17 February 1972, Winchester (VA) Evening Star, “Valley Folk Lore” by Elmer L. Smith, pg. 33, col. 2:
She’s so ugly, she would make a freight train take a dirt road.
 
9 January 1976, Corpus Christi (TX) Times, “He’s busier than a one-armed bass player” by Ron Powers (Chicago Daily News), pg. 4C, col. 1:
Had a girl; she said your face could make a freight train take a dirt road.
(A story about singer-songwriter Tom Waits.—ed.)
   
16 April 1976, Richmond (VA) Times-Dispatch, “Music” by C. A. Bustard, pg. B-11, col. 2:
(Tom—ed.) Waits is a funny, obtuse character, consciously sleazy and, to quote him, “ugly enough to make a freight train take a dirt road.”
 
28 July 1980, Seattle (WA) Times, “Political slogan” by Walt Evans, pg. B2, col. 1:
Joe Cannon said he saw a girl so ugly “she’d make a freight train take a dirt road on a muddy night.” Now that’s ugly.
   
Google Books
Redneckin’:
A hell-raisin’, foot-stompin’ guide to dancin’, dippin’, and doin’ around in a gen-u-wine country way
By Kathryn Jenson
New York, NY: Perigee Books
1983
Pg. 20:
“She’s so ugly she’d make a freight train take a dirt road.”
 
Google Books
The Reader’s Digest
Volume 124, Issues 741-746
1984
Pg. 149:
“He’s so ugly he’d make a freight train take a dirt road.”
   
Google Books
Comic Support:
Second Bananas in the Movies
By Ronald L. Smith
New York, NY: Carol Publishing Group
1993
Pg. 43:
At one event he knocked everyone on the dais from Johnny Carson (“He’s an Episcopalian—that’s an Off-Broadway Catholic”) to Roy Rogers and Dale Evans (“The Lunt and Fontanne of the fertilizer set”) to Yogi Berra (“He’s got the kind of face that could make a train take a dirt road!”).
   
AZLyrics
ZAC BROWN BAND LYRICS
“Different Kind Of Fine” (2006)
She make a train take a dirt road
Make it stop on a dime
Make ‘em wonder which way to go
Make a man change his mind
 
30 October 2006, Paris (TX) News, “It’s about the journey, not the destination” by Dr. Tom Newbury, pg. 4, col. 2:
There’s an old joke about a person ugly enough to make a freight train take a dirt road. It doesn’t matter if said person happens to be a man or a woman.
 
Google Books
To Love a Texan
By Georgina Gentry
New York, NY: Zebra Books
2007
Pg. 105:
She’s so plain, she’d make a freight train take a dirt road to avoid her.
   
A Way with Words
Make A Train Take A Dirt Road
Posted by Grant Barrett on May 31, 2014
(...)
Make a Train Take a Dirt Road
If she’ll make a train take a dirt road, does that mean she’s pretty or ugly? Nicole from Plano, Texas, overheard the idiom in the Zach Brown Band’s song “Different Kind of Fine.” The idea is an ugliness is so powerful it can derail a train. But as Zach Brown sings, looks aren’t all that makes a lady fine.