MacArthur Causeway Bridge
Photo taken by Phillip Pessar
License: Creative Commons Attribution (CC BY)
BH Photo #341691
Wikipedia has the following history about this bridge. It appears that it had some work done since it's original conception:
"In the late 1910s, with the deteriorating wooden Collins Bridge (now, the Venetian Causeway) as the only direct land route between mainland Miami and the barrier islands of Miami Beach, construction on the roadway began in 1917. The roadway, dedicated as the County Causeway, was completed in 1920. Watson Island was reclaimed surrounding the western end of the roadway, completed in 1926.
Having undergone several lane and structural expansions following opening of the original two-lane road, the State Road Board and Dade County Commission voted to rename the causeway in honor of World War II General Douglas MacArthur in 1942. The causeway was accessible from mainland Miami via Biscayne Boulevard and intersecting side streets through the 1990s, when replacement of the western- and easternmost spans and construction of direct highway access to I-395 began. The eastbound lanes of the bridges were completed in 1995, and westbound lanes finished in 1997."
This explains the "modern look" and so many lanes.
It looks far to new to have been built in 1920. They also wouldn't have built an 8 lane one with shoulders.