sentences:  Currently only Cologne and—Troisdorf in the Rhein-Sieg district—have direct connections to the airport via lines S13 and S19 of the S-Bahn, providing a service every 20 minutes on week days.There is an hourly service to the airport station via Regional-Express line RE 6 (the Rhein-Weser-Express) to Minden and the Regionalbahn RB 27 (the Rhein-Erft-Bahn) along the East Rhine Railway (Cologne–Troisdorf–Bonn-Beuel).Frequent connections are not possible, since the line carries dense freight traffic.