The MIO system in Cali pioneered in 2009 the use of dual buses, with doors on the left side of the bus that are located at the height of high-level platforms, and doors on the right side that are located at curb height. These buses can use the main line with its exclusive lanes and high level platforms, located on the center of the street and thus, boarding and leaving passengers on the left side. These buses can exit the main line and use normal lanes that share with other vehicles and stop at regular stations located on sidewalks on the right side of the street. For the system to work, users can receive "credit" on the electronic cards: in this manner, passengers who have no money left on the cards can take the bus at sidewalk stops where there is no possibility to recharge these cards. This means that the balance in the card can be negative, up to two ticket fares, so passengers can take the bus in the street and recharge the card once they reach a main line station. As the card itself costs more than the maximum negative balance, the passenger has no incentive to default on negative credit. Transmilenio in Bogotá followed suit in 2014 also creating routes that can use main line stations and regular sidewalk stations, but instead of giving credit to passengers to allow boarding the bus on sidewalks, published a map readable in smart phones giving the location of a dense network of 4,000 recharging points, located in internet cafes and other business, that use a swipe-card terminal for recharging. This system has the additional benefit of diminishing queues on main line stations.