Project will incorporate a BRT line to ease traffic congestion.
The four-lane dual carriageway is now 99% complete.
The road begins at Mlolongo, connects JKIA to the CBD, and ends in Westlands.
On completion, it will be the third highest bridge in Africa.
The project has been delayed by land compensation disputes.
The project has a contract sum of $163m (Sh18.7 billion).
The project is co-funded by the Japan Int. Cooperation Agency.
The airfield will be located at Gatuanyaga Village, Thika East.
The 457-metre bridge replaced a causeway built by colonialists in 1929.
The 70km road will be upgraded to bitumen standards.