If you step on broken glass or a dirty needle outside in a park what are the chances of getting blood born viruses like hepatitus or hiv?

Depends: On how long the blood has been there and whether or not it has dried. Both HIV and the hepatitis viruses will not live very long outside the body. They require living cells for their own survival, so if the blood has dried, been subjected to changes in temperature and other conditions it is unlikely to present a threat. Best is to be tested or prophylaexed if there is any question.

Viral infection risk: It is well known that hepatitis c in this setting is much more likely to still be contagious. Hiv is more fragile and does not survive well outside of a body or on inanimate objects. If you have an injury like this it is wise to get into a good expert physician rapidly.