The cyclist entered his plea by mail on Friday under a plea agreement with prosecutors, closing the case and avoiding a court appearance. Two other charges, failing to report an accident and speeding too fast for conditions, were dismissed under the agreement, which was first reported by the Aspen Daily News.
Court records show Armstrong paid $238.50 to cover court fees and a $150 traffic fine.
Armstrong's girlfriend, Anna Hansen, initially told police she had been driving home from an Aspen Art Museum party Dec. 28 when she lost control of Armstrong's GMC Yukon on icy roads, hitting the cars. She said she drove because "Lance had a little bit to drink," according to police reports.
Detectives later interviewed Hansen, who eventually told them Armstrong was driving but the couple had decided to let her take the blame. She also retracted her statement about Armstrong being unable to drive because he had been drinking. None of the charges against Armstrong involved driving under the influence.
"We've had our family name smeared over every paper in the world in the last couple of years and honestly, I've got teenagers, I just wanted to protect my family," Hansen told police, the reports state.
Police say Hansen and Armstrong left the scene before police arrived. However, they say Hansen ran up to the house near the damaged cars and apologized to a man who had been renting one of them, promising to pay for the repairs.
Deputy District Attorney Andrea Bryan said it is fairly common for people to reach plea deals in such cases and to enter pleas by mail. Careless driving can be punished by between 10 and 90 days in jail and a fine from $150 to $300 but jail time in such cases is rare, she said.
Prosecutors reserved the right to seek restitution for the damaged cars but Bryan said she believes Armstrong has already done that voluntarily.
Armstrong won the Tour de France every year from 1999 to 2005. Those titles were stripped after a massive report by the U.S. Anti-Doping Agency detailed the use of performance enhancing drugs by Armstrong and his U.S. Postal Service teammates.