It’s the shuttle bus between the airport in Kuala Lumpur and Sentral, the central transportation hub. It leaves every half-hour and costs either $2.70 or $3 depending on which company you use. The trip into town takes about an hour, depending on traffic. They run from about 4 AM until about midnight. Get to the airport after the last bus leaves? Not likely, but, if you do, sleeping at the KL airport is easy, but uncomfortable.