Be careful. If you're not well trained in sprinting and/or fully warmed up, you could pull a hamstring in an all out sprint. If you have hills nearby, hill sprints are safer for the average joe.
Bodybuilding.com - Charles Staley & Keats Snideman - Why Hill Sprints Are The Fastest Way Of Getting Strong, Fast, And Lean.
The hills by me aren't quite as steep or rugged as the ones in the article, but any hill that slows your max speed a bit should work.