what does"the four-ton Lincoln, with Greer at the wheel"mean? “Meanwhile the motorcade was forming. It was a set piece for the Secret Service, with variations to allow for the unaccustomed presence of the Vice President. The luggage truck and a pilot car, manned by local police, cruised a quarter-mile ahead, sizing up the route. The motorcade proper was led by a police car whose passengers included the Secret Service man stationed in San Antonio and the Washington agent who had advanced the city. Then came the feature attraction: the four-ton Lincoln, with Greer at the wheel, Kellerman beside him, the Connallys on the jump seats, and the Kennedys in the rear. ” what does"the four-ton Lincoln, with Greer at the wheel"mean? Thanks!