Emergency Braking

When a train goes into emergency braking do (or can) the wheels lock up? Wouldn't actually increase the stopping distance of the train? Or am I missing something here?

Variables, such as total weight on wheels, single or double clasp brakes, and adjustment of brake linkage would determine whether the wheels lock up, or not.

To simply answer your question... Yes, the wheels can lock up, and that would make the braking less effective.