Running is for marathoners, fitness enthusiasts and ironman competitors. Roadwork is for boxers. Traditional roadwork shouldn’t necessarily be approached the same way. Instead it should be exactly what it says, work on the road.
The goal of your roadwork routine, just like it is with every other aspect of your training, should be for it to apply specifically to boxing. This means, among other things, that it must incorporate variety. Like the characteristics of a boxing match it should include, bursts of action, moments of lesser activity, lateral movement, forward and backward motion and periods of heightened resistance. Each component has its place in the ring, so it should also have its place in your roadwork training.
A boxing match invariably has moments of heightened activity, where the action heats up, exchanges are more intense and the fighter is required to respond and retaliate. These bursts of intensity can be replicated in training with interval running or sprints. Incorporating sprints within the distance running exercises works well because it requires prolonged endurance coupled with intermittent high intensity cardiovascular demands. These bursts can be any length of time/duration, but obviously the longer you can work up to and extend these moments of high intensity, the better prepared you will be to meet any kind of attack (or mount one of your own) when that time comes in the ring.
Another spin you can put on this interval-type of training is to incorporate short plyometric drills or body movement exercises at specific points during the run. These can include a series of burpees, squat jumps, pull ups on a tree limb, push-ups...virtually any exercise that requires an increased pace, a new demand on the system and added intensity. Boxing is unpredictable so even long distance roadwork should be approached with that in mind.
Unlike most roadwork routines, boxing confrontations seldom happen along one plane of engagement. You are typically moving in a side-to-side fashion as much, if not more often, than you are moving forward or backwards. In order to replicate that into your running routine you can simply incorporate a shuffle step, both on the right and left sides. This requires more effort from the hip flexors and inner thigh muscles than just your ordinary forward motion run will, but will condition you to be quicker and more adept at lateral movement. You can use better side-to-side movement to throw your opponent off, punch from constantly changing angles and create openings that don't always happen from attacking from the same position.
Moving forward is pretty much captured with traditional long distance running, but the missing component is resistance. Seldom are you allowed to walk forward without meeting some type of resistance, so to better train yourself to meet that demand, running on an incline to increase resistance is beneficial. Or if you have a willing coach or training partner, you can add a resistance cord that drags your partner along behind you. If you have a running partner you can even take turns with who leads and who provides resistance, that way you both work different muscles and get more variety when pulling your partner versus working against him.
No matter how aggressive of a fighter you are, there are times when you have to move backwards, give ground or retreat for better positioning. You have to move backwards often in a fight, so why not run backwards? Some studies have been done that prove that "100 steps in reverse produces the same benefits as 1,000 steps straight ahead", producing better cardiovascular fitness results than traditional running. Running in reverse has been known to show significant decreases in oxygen consumption and undeniably reduces the impact on joints.
All of these approaches change-it up, hit on different muscular demands and provide slight variances in cardiovascular conditioning. There are endless approaches to running and all sorts of variations, but what's really most important is to design a routine that replicates the demands you'll face in the ring. To get the most out of it, the roadwork you do should apply to boxing. If all you're doing is going for a jog or just running, you may get in decent shape, but you'll never get fighting fit.