  We prove that an open manifold with nonnegative Ricci curvature, linear
volume growth and noncollapsed ends always splits off a line at infinity. This
completes the final step to prove the existence of isoperimetric sets given
large volumes in the above setting. We also find that under our assumptions,
the diameter of the level sets of any Busemann function are uniformly bounded
as opposed to a classical result stating that they can have sublinear growth
when ends are collapsing. Moreover, some equivalent characterizations of linear
volume growth are given. Finally, we construct an example to show that for
manifolds in our setting, although their limit spaces at infinity are always
cylinders, the cross sections can be nonhomeomorphic.
