It happened around 2:30 a.m. on westbound I-30 near Oakland Boulevard.
Fort Worth police said several people had stopped to help with an accident that happened earlier.
Many were outside of their vehicles when an 18-wheeler hit them and burst into flames.
Steve Franklin was killed. His wife, Tracy, was taken to JPS Hospital in Fort Worth with serious injuries.
Mary Hernandez, a mother of three, and her friend, Veronica Gonzalez, also died.
Gonzalez's fiancée, Ely, was also badly hurt and taken to JPS Hospital in Fort Worth in critical condition.
Ely's younger sister, Clarissa Banda, initially went to the hospital but later died from her injuries.
Gonzalez's family told FOX 4 that everyone had just gotten together for a party to celebrate she and Ely's engagement.
Gonzalez's family is now raising money to pay for the funeral. They say Gonzalez was not employed and didn't have life insurance.
A GoFundMe account has been set up for Gonzalez at http://www.gofundme.com/rsrp47y
Donations can also be made by calling Calvario Funeral Home in Dallas at 214-946-8165.
The truck driver was among those with only minor injuries.
Police are still looking into what caused the wreck.
The truck was carrying the Sunday edition of the Fort Worth Star Telegram.
FOX 4 is on YouTube -- http://bit.ly/fox4subscribe