Which front is a head on collision or neither warm nor cold air moves

Stationary wave fronts are formed when two air masses of different densities and temperature range push each other but unable to move the front in any direction.

Explanation:

Weather Fronts

When collision happens between air masses of two with varied densities and the temperature, they form  a front. These air masses also differ in humidity. When a cold front and warm front generated and push each other equally, the net force turns to be zero and there is no movement in any of the front.

By this, both of the fronts form a stationary row which separates both the fronts. Both kind of winds flow perpendicular to each other rather than parallel and this what holds the stationary front in place.

If the winds change the directions, the front may also move in the direction of the wind which is dominating the the other one. The weather seems to be often cloudy with this front. Hence, in the state of the formation of a stationary front, neither warm nor cold air moves parallel.