The sale is the first initial public offering of a trucking company in six years.
Overnite is one of the biggest less-than-truckload carriers in the United States, with 208 service centers, about 6,000 tractors and more than 22,000 trailers. It is mostly nonunion and operates under two names: Overnite Transportation and Motor Cargo Industries.
Union Pacific, which bought Overnite in 1986 for $1.2 billion, said it was selling after expected "synergies" between the railroad and trucking units didn’t occur.
According to filings at the Securities and Exchange Commission, Union Pacific expects total proceeds of $522.5 million from the sale of 25 million shares at $19 each and 2.5 million additional shares if there is more demand. UP officials said they will use the proceeds to redeem $500 million, or one-third, of its convertible notes sold in 1998.