From 1.01 Pilot (episode)
In 1981, Constance Welch, aged twenty four, drowned after she jumped off Sylvania Bridge, near the Centennial Highway in Jericho, California.
An hour previously she had called 911, reporting that her two children drowned in the bath after she briefly left them unattended. In reality she drowned the children after finding out her husband had been unfaithful.
Since her death she haunted the highway, appearing as a hitchhiker to young men. Constance would beg to be "taken home", but then protest that "she could never go home". She would then will the young men after she tempted them into being unfaithful. Ten men have died on the same five mile stretch of highway.
On the voicemail message John leaves Dean, there is EVP of Constance saying "I can never go home".
When Dean and Sam got her to enter her old home, the ghosts of her two children appeared to her and her spirit was destroyed.