What are you trying to accomplish with your roadwork? When training for boxing that question must always be in your mind- nothing is ever done just to do it. I would humbly suggest that your medicine ball routines etc.. be separate from your "roadwork"
To me there are two types of roadwork, maybe three. One is the two miles of jogging you do three times a week all the time, to stay in shape. The other is the 3-4 miles you do in the obscenely early morning hours while prepping for a fight. This need not be running, per se, just a brisk walk while you shadow box, think about what is coming and force yourself to do what you don't want to do. The third type, I believe, is the most wothwhile.
That is where you sharpen your wind. You are fighting 6 rounds? OK. Start with a very rapid 1 minute walk. Then, over three minutes, alternate running, jogging, and springting. Then walk very rapidly for a minute, then three minutes of sprinting, running, jogging and so on.
The purpose of roadwork is to sharpen your wind for the purpose of fighting- when you have fierce exchanges, lulls in the action and so on.