Make Mine a Mystery: Reader's Guide to Mystery and Detective Fiction by Gary Warren Niebuhr (2003) defines a traditional novel this way:
"In a traditional novel, the action uses violence to establish the seriousness of the crime without trivializing its importance or glorifying its horrifying effects. Most violent action takes place on stage but is not graphically described. The emphasis can be equally on the perpetration and solution of the crime. The protagonist's goal is to find a solution to the crime, but not necessarily through the administration of justice by an official court of law. However, the intent of a traditional novel is to restore the balance of right and wrong in a society gone wrong."
Laurie King's Mary Russell novels (which I love!) are an example of the historical/traditional. Dog On It is an example of a traditional with a humorous twist to it. Sue Grafton's alphabet series is an example of traditional mystery as are the Adam Dalgleish novels of P. D. James. The traditional novel is essentially a book that combines elements of the cozy and the hard-boiled without tipping all the way either direction.
This post is part of the Crime Fiction Alphabet 2012 at Mysteries in Paradise.