Florida “Sacrificial” Roads Projects

Recognizing the increasing maintenance and replacement costs for coastal roads in Florida due to more frequent flooding and storm surge, the Federal Highway Administration (FHWA) – Eastern Federal Lands Highway Division (EFL), assisted the National Park Service and other partners designing specific that are prone to be frequently washed out to have minimal environmental impact. Rising sea levels and coastal storms, which are projected to increase in intensity as a result of climate change, are creating more challenges for building and maintaining transportation infrastructure along coastal shorelines.  EFL replaced roads in Florida’s Gulf Islands National Seashore and Merritt Island National Wildlife Refuge with innovative construction materials and techniques that would be cost-effective over the lifecycle of the road, compared to traditional roadway designs, and would help minimize impacts to the environment and wildlife in the event of a washout.

In recent years, intense storm events caused moderate damage to total washout of the roads in Gulf Islands and Merritt Island. NPS incurred additional expenses due to the frequent maintenance and road replacement required as a result of the storms. Washed out road materials also had the potential to be detrimental to habitats in the national seashore and wildlife refuge. In response to these financial and environmental concerns, NPS, EFL and partners undertook road projects in 2006-2007. The roads were designed as “sacrificial” roads and would wash out with minimal environmental consequences when a storm surge hits. They were designed as temporary cost-effective solutions to the problem of repeated washout.  Eventually, NPS may have to consider alternative strategies as these areas become inundated with future sea-level rise.

Gulf Islands National Seashore:

The Gulf Islands National Seashore, which is managed by the National Park Service (NPS), includes barrier islands located along the Florida Panhandle and along Mississippi’s coast; the sacrificial road built by EFL lies on the barrier island near Pensacola, Florida. The road leads to Fort Pickens, a popular destination for visitors, at the western end of the barrier island. Prior to undertaking this project, the road was a conventional paved road with an aggregate base covered with layers of asphalt. However, portions of the conventional road had washed out twice in recent years, including during 2004-2005 hurricanes, causing impacts to natural habitat when aggregate and asphalt pieces littered the white sand beaches of the National Seashore. 

After the second washout, EFL worked with the National Park Service, Florida DOT, and a consultant to identify alternative design options that could lower costs over the lifetime of the road and minimize impacts to the environment. They chose a road structure with a cellular confinement system (CCS) as the base instead of a traditional aggregate base.  A CCS is honeycomb-shaped, three-dimensional structure that can be filled with aggregate or other type of crushed material to provide structural stability. For this project, EFL used sand to fill the CCS, which will minimize cleanup in the event of a washout. A CCS base must also be covered with a minimum 1 inch thick material because it will buckle if it loses its fill material. Here, the CCS was covered with two layers of asphalt: 3.5 inches of course asphalt and 1.5 inches of finer asphalt, a thicker total amount to make up for stability lost by using a CCS compared to a standard aggregate base. Even though a washout will still generate some debris from the CCS structure and the top asphalt layers, the debris will interfere less with the beach environment than a gravel-filled CCS or debris from a conventional paved road.     

Another design option EFL considered was “cement stabilization,” a mixture of cement and sand for the base. Cement stabilization would have been better for the environment because only the top layers of asphalt would need to be cleaned up after a washout. However, cement stabilization offered less durability than the CCS structure, and would only be more cost-effective in the event of very frequent washouts.

Although CCS is comparable in cost to a AC paved traditional road, it is expected to be a more cost-effective option over the long term for a coastal road such as this that is expected to wash out at some point. Maintenance costs are much less costly over the lifetime of a CCS road compared to a standard gravel-base road, and in the event of a road washout, cleanup costs are also less significant than for a standard road.  EFL expects the road as designed will last 8-10 years or until a major storm impacts the road.  The road has now been in place about 8 years and is showing signs of asphalt distress that will require minor maintenance.  Road performance during the 8 years met or exceeded expectations.

Anticipating a washout of this sacrificial road in the future, the NPS added a “floating” amount to its annual funding cycle that will be used to rebuild the road when necessary. For a longer-term solution, NPS is planning to reroute a 1.55 mile section of Fort Pickens Road, which will involve removing a portion of the existing roadway and allowing that area to return to natural conditions. Construction on the realignment is expected to be completed in February 2016. The NPS is also planning a ferry system to provide alternative transportation from Pensacola to Fort Pickens, in recognition that the roads may wash out too frequently to be replaced and may become permanently inundated at some point. For a discussion of the future Fort Pickens Ferry System, see additional case study.

Merritt Island National Wildlife Refuge:

The Merritt Island National Wildlife Refuge, which is managed by U.S. Fish and Wildlife Service (FWS), is on the eastern coast of Florida near Cape Canaveral, spanning portions of Brevard and Volusia counties. EFL implemented two roadway projects in the Refuge similar to the Gulf Islands road: Black Point Wildlife Drive and Shiloh Marsh Road.  The existing roads consisted of unpaved silty sand embankments that served multiple functions including dikes for water management and also to protect wildlife.  However, the unpaved roads required significant and frequent maintenance and had experienced washouts during hurricanes and storms.  For the two projects, EFL in partnership with FWS considered a number of road paving material alternatives, including CCS, aggregate-only (with no paving on top), coquina shell surface, and a dirt road mixed with a glue-like material (lignosulfonate) to stabilize the road. 

Black Point Wildlife Drive: Black Point Wildlife Drive is an unpaved road approximately five miles long with swamps on both sides. Because it is a loop road, it also experiences storms from all angles. For this road, EFL and FWS selected a four-inch thick CCS base filled with limestone and covered with two inches of limestone. Limestone was chosen to fill the CCS because it met natural requirements of the refuge and encouraged drivers to drive slower than a more conventionally-paved road would have. A cost analysis also indicated that construction of the CCS filled with limestone was comparable or slightly cheaper than a traditional road base paved with asphalt. The new road has lasted for over seven years with no damage to the underlying CCS base; limestone has some cement-like properties and likely has contributed to a more durable structure than a loose aggregate fill for the CCS would have. It has required only minimal maintenance in areas where the top layer of limestone has washed out. 

Shiloh Marsh Road: Shiloh Marsh Road is an unpaved road approximately three miles long that runs along a portion of the Indian River Intracoastal Waterway in the Refuge. For this project, EFL and FWS chose a coquina shell surface for higher portions of the road and a CCS filled with stone for lower portions of the road. They used the CCS for low portions because the subgrade portions of the road are frequently covered in water, and a loose surface material would have washed out very quickly. Although the road has mangroves on one side that help to shield it from storm surge, the road nonetheless washed out at 90% completion due to a hurricane. 

All three of the sacrificial road projects were managed by FHWA-EFL. Eastern Federal Lands provides engineering assistance and solutions for roads under the jurisdiction of federal land management agencies (including in national parks and wildlife refuges) and other federal lands roads in the eastern half of the United States and U.S. territories.

 

This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on January 29, 2016.

 

Publication Date: 2007

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