Posts for swing gates should ideally be larger and strong so they don't bend with the weight of the gate causing the gate to drag on the ground, but these can be expensive so lighter weight posts can be used if braced correctly. 

A fence panel attached to the post in line with the closed gate will brace the Gate Post significantly in the closed position so long as the fence rails are firmly attached to the posts, it will have little effect when the gate is open but if the driveway slopes down from the road this isn't a problem because it has nothing to drag on other wise you'll need to brace it in that direction too.

To brace the open position a metal or timber compression brace can be used.

A Compression and Tension Brace

Galvanised pipe or box section (SHS) can be used as a compression or tension brace for a post but must be concreted securely into the ground. Can be used within a front fence line for the gate closed position (under tension as illustrated below) or fitted parallel to the open gate to brace the open position (under compression).

A Wire as a tension only Brace

Must be secured firmly into the ground using a metal or timber post concreted into the ground. Will blend in behind wire fencing but is only suitable for bracing the post for the closed gate position.

Do not use a wheel to support the weight of a gate as this can make a gate difficult to open and close and not suitable for automation as it provides to much resistance for an automatic operator.

DO NOT Fill a hollow metal post with concrete It can stiffen it up considerably but makes it very difficult to drill into for fitting hinges and running cables inside for installation of an automatic operator, digital keypad or intercom.