This paper explains the concept of the implementation of multi-modal traffic in TRANSIMS. For this, the paper has two parts: A first, explaining the TRANSIMS design using examples from car-only runs, and a second, which explains the provisions for multi-modal trips. The emphasis of the paper is on the second aspect. TRANSIMS starts by assuming that all activities are located on the walk network, and in consequence any trip connecting two activities at different locations will involve walking at the beginning and at the end of the trip. Transitions to other modes are made via transfer points and transfer links. The activities generator of TRANSIMS provides the preferred mode to reach an activity, and the multi-modal router routes these trips. The traffic microsimulation reads these plans, executes them in detail if the corresponding mode is implemented, and ``believes'' them if the mode is not implemented. The latter means that for a non-implemented mode the traveler is just moved to her/his destination according to the timing provided in the plan; no interaction between travelers is computed in this case. This also gives a clear implementation path to the addition of realistic pedestrian modules. The TRANSIMS feedback mechanism provides an answer to some of the usual conceptual questions, for example of where to place the mode decision (into the activities planning or into the routing) or what to do about non-additive link costs.