H.C.
I had a similiar problem with both of my kids at this age. My older one would take off down the street, and I had to coordinate with my neighbors at times to snag him (where I was pregnant with my second one, and darn that kid was fast). My youngest son, I had to take after him a couple of times about leaving the yard (while we don't live in a high traffic area anymore, it's still dangerous). What we ended up doing with him, was I stood with him, out close to the roadway as cars drove by. It took a couple of big trucks stirring up the dirt and scaring him to tightly grip my leg, before he started to see the dangers.
That didn't fully work, but we also got him a small "Scooter" (a little plastic motorcycle type) that slowed him down quite a bit as he rolled it through the grass.
But otherwise, all I can think to suggest, is that you maybe take him to a park where he can run free, and make that "A safe place" versus the yard -- "we don't run in the yard, but only in the park".
Good luck.