MetroLink
The Jefferson Memorial is easily accessible from St. Louis' MetroLink Lightrail. Board at any station and exit at Laclede's Landing and follow the signs to the Memorial (a five minute walk). The trip from Lambert National Airport to the Jefferson Memorial Lambert Airport is 28 minutes, with departures to and from Lambert every 15-20 minutes.
MetroBus
MetroBus has routes that run close to the park. Use TripFinder to plan your route by typing Gateway Arch into the Destination Point field.