Decks, Patios, Porches and Docks - Foot Bridge over a Creek

I am wanting to build a simple foot bridge over a creek. The span 16' and 3' wide. I want to make it flat with 2X6s across the top. I am trying to decide what to you use as the span. Will a 4X4 be enough or should I use a 2 2X6s to make a 4x6? Is that enough? Would love to hear your input. If anyone has any load information that would be helpful.
Thanks
Doug

If you are spanning 16 feet, dimensional lumber is pretty much out of the question. A 4X12 would barely make it.

Go down to the local power company and see if you can swap some good stories and Redman Golden Blend for 2 used power poles. Since they will be under the structure, they won't be seen and should last as long as you need them. Our local EMC just replaced a few hundred wooden poles with metal ones to handle substation power as well as the existing lines. Not too hard to bargain for them as they cut them off at the ground and can't be used again (too short).

Good call Larry -- I hadn't thought about power pole cut-offs!!