Wayne Roustan steers you clear on SoFla roads.

Doctor Detour answers your transportation questions.

Q: When traveling up north along Florida’s Turnpike or Interstate 95, I notice speed limits in construction zones are reduced to 60 mph. Speed limits along I-75 during the long construction in Broward and Miami-Dade counties have not been similarly lowered, despite much, much heavier traffic. Why is that? Doug Quara, Coconut Creek.

A: It depends on the roadway. The state established speed limits of up to 70 mph on interstate highways, 65 mph on a four-lane divided highway outside of urban areas with populations over 5,000 and 60 mph on other state highways.

Florida law says traffic engineers should determine the speed limit through roadway construction zones and what signs should be posted to warn drivers to slow down. Generally, speeds are lowered 10 mph below the posted speed limit where construction crews are working.

On I-75, most of the express lane construction was done in the median and not on the highway itself.

Q: One of the biggest mistakes Fort Lauderdale has made is to put a roundabout on a very heavily traveled Northeast 13th Street and Dixie Highway. Why was this done? Richard Iacino, Fort Lauderdale.

A: Roundabouts are specifically designed to reduce the

risk of crashes. The Florida Department of Transportation says roundabouts lower fatal crashes up to 90 percent and injury crashes about 75 percent.

Northeast 13th Street used to have two lanes in

each direction with traffic signals at Dixie Highway. Now it has one lane east and west, with one of 14 existing roundabouts in Fort Lauderdale. There are more to come, said city spokesman Chaz Adams.

Many are located on neighborhood streets to help create a safer environment for people walking to

school, riding bikes, or walking their dogs.

All of the roundabouts have come at the request of residents who wanted to reduce speeding and decrease cut-through traffic within neighborhoods, he said.