  Colliding branes without $Z_{2}$ symmetry and the formation of spacetime
singularities in string theory are studied. After developing the general
formulas to describe such events, we study a particular class of exact
solutions first in the 5-dimensional effective theory, and then lift it to the
10-dimensional spacetime. In general, the 5-dimensional spacetime is singular,
due to the mutual focus of the two colliding 3-branes. Non-singular cases also
exist, but with the price that both of the colliding branes violate all the
three energy conditions, weak, dominant, and strong. After lifted to 10
dimensions, we find that the spacetime remains singular, whenever it is
singular in the 5-dimensional effective theory. In the cases where no
singularities are formed after the collision, we find that the two 8-branes
necessarily violate all the energy conditions.
