Atlanta's rapid transit network was extended to Hartsfield International Airport Saturday, making the city the fourth in the United States with a rail station in its airport terminal.

The train-to-plane began operating at noon, fulfilling one of the 17-year-old transit authority's major goals.

The $30 million airport station was completed under budget and ahead of its originally scheduled December opening date. About 7,000 riders a day will use the new station, Metropolitan Atlanta Rapid Transit Authority officials estimate.

The trains will run every 12 minutes, with a 15-minute ride between the airport and downtown.

The three other cities with in-terminal rail stations are Chicago, Cleveland and Philadelphia.