4-63. Commanders establish the priority of mobility support based on the mission variables. This support consists mainly of reducing obstacles and improving or constructing combat roads and trails to allow tactical support vehicles to accompany combat vehicles. Commanders coordinate carefully to ensure that units leave lanes or gaps in their obstacles that allow for the repositioning of main body units and the commitment of the counterattacking force. CBRN reconnaissance systems also contribute to a force’s mobility in a contaminated environment by marking contaminated and clean routes as well as providing CBRN expertise while developing alternate COAs.