This is the Rickenbacker Causeway today: As many as nine highway-style lanes of speeding, noisy traffic, bordered on either side by a narrow string of popular beaches, winding paths shared by throngs of cyclists and pedestrians, and perilously unprotected but heavily used on-road bike lanes.
Mixed in are a big public high school, a marina, federal and University of Miami marine-science buildings, restaurants and other attractions.
At times, after a heavy rainstorm that swamps the low-lying roadway or a special event on the grounds of the historic but long-closed Miami Marine Stadium, the causeway — the only way in and out for residents and visitors to paradisial Key Biscayne — becomes a veritable parking lot…