Caltrans is studying the durability and performance of its Barrier-Transfer Machines, also known as "zippers." Each BTM moves concrete dividers that separate the Express Lanes one lane over. During April, two BTMs will move the barriers two lanes over, giving three lanes in the direction of the rush hour commute. Express Lane drivers will have the benefit of having three lanes instead of two. Drivers going the other direction will be limited to only one Express Lane.