ARL operator SRT Electrified Train Co (SRTET) will team up with tourism and airport agencies to operate a city check-in system at the Makkasan station similar to those in Britain, Hong Kong, Malaysia and France, said chief executive Peerakan Kaewwongwattana.
The check-in and luggage loading systems need to be improved, and the process will be finished by year-end or early next year, he said.
"As Suvarnabhumi airport has experienced high passenger congestion, the 10,000 square metres of the ARL's Makkasan station is capable of transporting 10,000 passengers a day," he said.
As well, frequency will be increased on the Express Line early next year, leaving every half hour compared with every hour at present, said Mr Peerakan.
Meanwhile, ARL trains currently average 12 minute headways compared with 15 minutes in July and 20 minutes in May. The headway for China's 300-km high-speed trains is three minutes.
A connection of the ARL's Phaya Thai station and Don Mueang international airport will also be completed by the end of 2015, Mr Peerakan said.
He said an environmental impact assessment has been conducted, and the bidding process will be completed by this year.
Covering 23-25 kilometres, the route will have six stations, with the Express Line stopping at one or two stations.
The ride will take no more than 45 minutes.
At present, 1.45 million commuters use the ARL each month, up 15% from last year. Of the total 55,000 commuters daily, 90% use the city line.
Meanwhile, SRTET has proposed buying seven new trains worth 5.2 billion baht, but the transport minister thought the cost too high.
The company, which is under the State Railway of Thailand, was asked to seek less-expensive trains.
A source who asked not to be named said ARL trains have managed to lower the train cost by 20% of the original estimate.