There are two common approaches to provide a continuous path for traction current that spans multiple track circuit blocks. The simplest method installs insulated track circuit joints on only one of the two rails with the second being a path for the return current and a ground for the track circuit rail. This has the disadvantage of only being able to detect breaks in one rail so the more popular two rail system uses impedance bonds to permit traction current to pass between isolated track circuit blocks while blocking current at track circuit frequencies.