Design-Build Helps Take Bite Out of Alligator Alley

Fri July 23, 2004 - Southeast Edition

Alligator Alley, as its name alludes, can be a treacherous place to drive, but not necessarily because of the reptiles.

This 75- to 80-mi. stretch of Interstate 75 in southern Florida, for some reason or another is the location for a large amount of car accidents annually. Between 1995 and 1999 the Florida Department of Transportation (FDOT) calculated there were 407 crashes along this stretch, with 56 of the accidents going off the road into the alligator-infested waters and 14 people dying, having drowned in the channels alongside the interstate.

I-75 runs the length of Florida from the north to the south, and then takes a sharp left turn in Naples. The west to east portion from Naples to Broward County, has become known as Alligator Alley.

The strip of road was previously the two-lane State Road 84, also known as Alligator Alley, but was gradually upgraded and officially became a four-lane continuation of I-75 in the early 1990s.

The section of road earned its nickname because it traverses Big Cypress Swamp and the sawgrass marshes of Water Conservation Area 3. Because of this prime location, alligators, as well as other wildlife, and rare species of birds can be seen lounging and frolicking in the canals alongside the roadway.

Because of the abundant wildlife in the area a fence was erected to prevent critters from running onto the roadway, but this wildlife fence was not meant to keep automobiles out of the water. A trend started occurring where cars were running off the road.

“Cars left the road and slipped under the fence, submerging vehicles in the canals, and people inside were dying,” explained Debbie Tower, public information director of FDOT District 1. “The fence would slip up [and down], so often there was no damage.”

This would make it difficult for police and rescue workers to locate where the car went into the water, and sometimes this delay in rescue efforts would lead to the drowning of accident victims.

The Florida Highway Patrol (FHP) brought this problem to FDOT’s attention.

In particular, the problem was discussed among the Community Traffic Safety Team, which includes law enforcement, rescue workers, schools and transportation leaders. The team discusses safety issues and typically works on projects of a smaller scale (less than $500,000) with grant money, but concerns regarding Alligator Alley were too large in scope and costs so the FHP asked FDOT if anything could be done.

FDOT realized an extra safety barrier might help in this area and decided to make the job a Design-Build project.

“We knew we could produce the project more quickly as a Design-Build,” Tower said. “Standard design is a two-year process.”

The Alligator Alley Safety Barrier project took just over a year from bidding to completion.

“Design-Build enhanced coordination and communication and allowed the industry to be innovative. That was important since we had no preconceived idea for the project.”

The department put out a Request for Proposal (RFP) in the fall of 2002. Three proposals for the Alligator Alley Safety Barrier were received and given a technical review. Each proposal was graded and scored on its technical aspects and cost, and the best combined score was tallied. Two proposals were strictly guardrails, but the third was a unique design that utilized a cable system with only some guardrail.

The ’Cornerstone’ of Good Design

Cornerstone Businesses Inc., in Zephyrhills, FL, was chosen for the project because of its original cable design. The cable guardrails were unique in that they have never been used before in Florida.

“FDOT did not have any specs for cable guardrails, but other states do such as North Carolina, South Carolina and Virginia,” said Ken Winsbro, vice president of Cornerstone Businesses. “Throughout our career, we have been involved with guardrail in other states and other states use cable. The benefit of cable is maintenance. A guardrail has to have asphalt underneath; that would have been a monumental task along a waterway. The ease of installation saved FDOT one-third of their budget.”

By using design-build, and the cable system, the project saved FDOT $2.9 million.

The cable barrier system uses two .75-in. (1.9 cm) galvanized cables anchored every 1,500 to 2,000 ft. (457 to 609.6 m) and located 21 to 27 in. (53 to 69 cm) above the ground, with 2,000 lbs. (907 kg) of tension provided by springs attached to the anchors.

“The cables act as a catch net and strengthen the existing fence,” Winsbro said. “The benefit is we used the existing fence [to mount the cables]. With the exception of the anchor blocks, there was no excavation.”

Another benefit to the cable system is that it is less obtrusive than guardrail. This is an added bonus in an area with natural scenery.

There also are solar-powered strobe lights attached at the anchors.

“The strobe lights are similar to the light on the back of a school bus. When a car hits the cable it pulls a trip wire that activates the light, which helps rescue workers locate the vehicle.”

The Intelligent Transportation System Working Group for FDOT is evaluating the possibility of enhancing this notification system even further by using a programmable logic controller along the breakaway switch circuit, or trip wire, that would send a notification via wireless and microwave communications to a Regional Traffic Management Center (RTMC).

This enhancement would speed rescue efforts even further because there would be a notification sent out rather than waiting for passing traffic to see the strobe light. This idea is in the very early stages of discussion and currently funding is not available for the project. Also, an RTMC still needs to be built in District 1. It is anticipated that there will be a construction letting for a Collier County RTMC in May 2005.

The cable barrier runs approximately 50 mi. along the western side of Alligator Alley, in Collier County. Currently, FDOT has no plans to install a cable barrier on the east Broward County side of Alligator Alley.

“The accidents have occurred predominantly in Collier County,” Tower said. “It’s important to understand that the cable barrier is a secondary safety measure. There is an area of clear recovery provided along the interstate. We were seeing an unusual trend of crashes where cars were going off the road, under the fence and into the canal just beyond. There are other areas along the stretch where the canal is farther removed.”

Contractors Become Heroes

The project’s design process began in January 2003, construction started in September 2003 and the project was completed in February 2004, on schedule and at a final cost of $4.2 million paid with toll revenue. In that short time, as sections of the cable were put into place, the system’s abilities were tested by five separate accidents.

“The first two were on the northbound side where the canal is five feet behind the fence. The cable kept them on dry land. One car was going 75 to 80 miles per hour into the fence, but the only thing that got wet were the front wheels. The lady walked away and said how relieved she was because she couldn’t swim,” Winsbro said.

“The other two hit the cable and rode along it for 50 to 100 feet, but it kept them out of the canal … There was minimal damage to the vehicles … Only grooves from where the car hit the cable.”

The fifth crash, heading southbound, hit a cypress tree, “It was sent airborne and missed the cable,” he said. “The car flipped over in the canal. One of our work crews saw it and hooked onto it and pulled the car out with a chain.”

FDOT is satisfied with the results of the cable safety barrier.

“It is working well. It’s been tested five times and no lives have been lost. The intent was to save lives,” said Tower.

(This article appears courtesy of the “Florida Transportation Builder.”)