Better Bridges
Tina Grady Barbaccia | May 8, 2011

The Bridge as Bat Cave

A sharp decline in bat numbers prompts Oregon’s Department of Transporation to build habitats into bridges.

By Tina Grady Barbaccia

Build a bridge, save a bat.

That’s what the Oregon Department of Transportation (ODOT) has done as part of its Oregon Transportation Investment Act (OTIA III) State Bridge Delivery Program, a 10-year, $1.3-billion program that is repairing and replacing hundreds of bridges across the state.

Colonies of Townsend’s big-eared bats such as these are exactly the sort of residents the Oregon Department of Transportation hopes to lure to its newly rebuilt Curtis Creek Bridge.

Knowing that bat numbers in the United States have fallen sharply since the 1960s, ODOT proactively incorporated bat habitats on bridge projects to promote roosting. Included in these measures was the development of an outcome-based Bat Habitat Enhancement environmental performance standard (EPS).

Aware of what a laborious process it could be to obtain permits for each bridge separately, ODOT initiated a program — environmental programmatic permitting — that incorporated both state and federal partners, which served as the process that brought together myriad agencies under one permit. This captured regulatory commitments on a program level versus a project level. The state and federal partners together formed the Programmatic Agreements Reporting and Implementation Team, or PARIT. The team met regularly to resolve any challenges and discuss common goals. This not only sped up the bridge permitting process, but it allowed the team to develop other innovations under the same programmatic such as wildlife passages and the Fluvial Performance Standard (go to for more information) — enhancements that may have been otherwise overlooked.

This photo was taken looking up toward the cave-type habitat on the Curtis Creek Bridge, constructed between two girders near the diaphragm on top of the supporting piles and pile cap. The bottom flange of the girders supports the floor of the bat habitat and a cutoff wall is constructed on top of this floor to create the cave. Access to inspect the pile cap and diaphragm is created on the opposite end of the cutoff wall.

The normal standalone project delivery process includes a biological opinion, and then an assessment that must be processed through each agency. “It can be a complicated, time-consuming process just to get everything lined up for one site,” says Geoff Crook, environmental manager for the OTIA III Bridge Delivery Unit. “Regulations are often prescriptive and define what you can and cannot do in a quantitative way. However, instead of having many permits with many agencies, a programmatic batches everything together. Our solution was to take a collaborative approach to deliver the program. Focusing on areas of mutual agreement — e.g., safety, economic development, efficiency and environmental stewardship — we developed a single set of environmental performance standards that meets the intent of all the contributing agencies’ regulations while allowing contractors maximum flexibility in how they achieved them.”

This allowed the biological opinion to be batched together to make everything eligible under one permit. The formation of a multi-agency PARIT team also allowed ODOT quick access to decision makers, which allows for quicker responses times and flexibility during design and construction.

Two cave-type habitats for bats can be seen in the center and far left of this photo.

“That is efficiency in and of itself,” Crook says. The streamlined process was also cost-effective. In a cost-benefit analysis of the return on investment for programmatic permitting in terms of cost avoided, return on investment (ROI) was $3.19 for every $1 spent, according to Crook. Using a traditional permitting approach, the ROI was 75 cents for every $1 spent. What’s more, the efficiency of putting together a programmatic permitting process enabled ODOT to wrap up the environmental portion of the 10-year bridge program this past fall. Originally set for completion in 2013, the environmental programmatic permitting team wrapped up its work in only seven years. By some estimates, it would have taken 50 years to permit all the bridges — nearly as long as the 75-year expected lifespan for the structures themselves — if the traditional permitting process was used.

One program, multiple agencies

In the development of environmental programmatic permitting, performance standards of multiple regulatory agencies were synthesized to satisfy multiple requirements under one permit.

The floor of a bat habitat and the bottom of the cutoff wall can be seen.

Included in the programmatic permit were standards for bat habitats. “We’d like to do something for the uplift of the species,” Crook says.

Bats are not a regulated species in Oregon, although in some states they are “endangered” or “threatened.” But bat numbers have been declining, so when the programmatic permit was being developed, ODOT worked with the Oregon Department of Fish and Wildlife and the U.S. Department of Fish and Wildlife to develop standards that could be rolled into the programmatic. The standard outlines a goal — to maintain, replace or improve roosting on bridges over waterways. This standard was only developed for bridges over waterways because this is where bats’ primary food source is.

ODOT wants to keep bridges bat-friendly because of the integral role the mammals play in the environment. In a single night, one bat may eat thousands of insects, including mosquitoes, which could carry West Nile virus, Crook says. Some bat species also serve as pollinators whose eating habits can help farmers reduce pesticide use, he adds.

“The Oregon Department of Transportation wants to keep bridges bat-friendly because of this beneficial role in the ‘web of life,’” Crook points out.

However, contemporary precast concrete structures lack the texture and crevices bats need to be able to roost, so ODOT biologists worked with their counterparts from the Oregon Department of Fish and Wildlife and the U.S. Forest Service to develop guidelines that help engineers design bridges with bats in mind. Instead of forcing existing populations of bats to relocate, ODOT integrates habitats into the bridge structures when they are rebuilt or adds them on in the form of bat boxes when a bridge is being repaired instead of being replaced.

“We developed plans to actually build bat habitats into the bridges,” Crook says. “As bridge designers are looking at bridge constraints and what kind of structure or material to use, they will consider incorporating a bat habitat. An integrated bat habitat is highly beneficial because it doesn’t need maintenance like wood does.”

The performance standard provides clear guidance to bridge designers about how to replace, maintain or improve suitable roosting habitats on bridge program projects, according to ODOT.

ODOT worked with regulatory agencies to identify which bats may or may not be on the bridge at the time of the bridge assessments by looking for current habitat use and whether the bridge could be used with slight additions or alterations. Biologists went out into the field with a flashlight at night to check the bridges for bat use and to identify which species were using the bridges, because this would impact the type of structure that would have to be incorporated into the bridge design or rehabilitation plans. “We developed plans to build bat habitats into the bridges themselves,” Crook says. “This walks the designer through what to consider. We are essentially building habitats for different bat species.”

A place to call home

At Better Roads press time, 88 bridges in the program were in compliance with bat habitation environmental performance standards, according to ODOT. The agency has verified that its bat habitats have been successful.

With the creation of a crevice habitat — one of three types of bat habitats on bridge structures — in the shallow box-beam bridge replacements to provide a roost for mouse-eared bats, inspectors found piles of guano, or bat waste, directly beneath the crevices shortly after construction. This served as evidence that bats were using the structures, the agency says.

The other two types of bat habitats that can be incorporated into a bridge include a cave-like or an “Oregon wedge” design.

With a crevice habitat, an integrated habitat is built into the concrete of the structure. This is a crevice type of habitat that incorporates box-beam girders or pre-cast concrete. A gap is placed between the boxes to provide a crevice that runs along the span of the bridge. “We can size the crevice appropriately for an ideal bat habitat,” Crook says, adding that 1/2 inch to 1-1/2 inches is standard for the crevice.

A cave-like, or cavernous habitat, is idea for the brown bat. An actual box is built into a span between box girders to provide an open area. The “Oregon wedge” is a simple plywood box designed to accommodate hundreds of bats at a time. The vertical box is typically affixed to the side of a bridge with a 1/2-inch crack, so bats can crawl up inside of it.

“This gives them a place to shelter and roost,” Crook says. The box can be placed in a beam or on the outside of it. Placing it in a beam is advantageous because it is darker and there is less temperature swing. However, the advantage to placing the box on the southern outer side is the quicker heat up of the concrete during the winter.

Bats like to thermoregulate; they need to maintain a certain body temperature. “Even though they roost in the dark, they need heat,” Crook says. “They move up and down within structures, depending on the time of day, so they can use solar radiation.”

If it’s really hot out, bats will work their way down on the diaphragm or crossmember to get more air flow and cool down, explains Randy Reeve, a senior scientist for Parametrix. Reeve worked for the Oregon Department of Fish and Wildlife at the time the EPS was being developed. However, concrete is a good heat sink, meaning it takes a radical temperature change before the concrete loses or gains heat, so if it’s cold out, the bats will work their way up to the top of the structure where there is more concrete around them and less exposure to the wind.

In erecting the bat habitats, Reeve says, masonry board on plywood is being experimented with to give the bats a better grip. Additionally, when bats are hanging in their roost, they are naturally going to lose bodily fluids through urination and defecation, Reeve says. “If this is done on wood for an extended time frame, the wood will start to deteriorate,” he says. “But concrete, which deteriorates slower than plywood, will be there for a long period of time without the agency having to worry about it etching or deteriorating.”

In some cases, contractors have installed 80-grit sandpaper onto the plywood forms so the bats have a nicely textured surface to grip during the roosting.

These bat habitat additions are just minor considerations in the design of a bridge, notes ODOT’s Crook. “It doesn’t affect the overall structure of a bridge.”

According to Bat Conservation International, transportation departments are ideally positioned to help re-establish bat populations, Crook says.

“By identifying existing habitats and proactively building roosts during bridge construction, often for less time and money, states protect and encourage bat populations, which in turn, have a positive effect on the ecosystem,” Crook says. “Like the bridges themselves, many of the innovations in heavy highway construction will be invisible to most people. But as builders and designers and employees of government agencies work together and share what we know about new ways of doing business, we’ll all experience the difference in diversity in habitats and species, and in cleaner air and water.”

The status of programmatic permitting for OTIA III State Bridge Delivery Program projects through Feb. 28, 2011.

Rescoped as “No Work” — 94

Designed Prior to Completion of Programmatic Permitting Process — 54

Alternate Permitting Process — 11

Programmatic Permitting Complete — 206


A Team Effort

The Oregon Department of Transportation (ODOT) worked with partners to streamline the environmental permitting process by forming the Programmatic Agreements Reporting and Implementation Team (PARIT) including:

Oregon Departments of Fish and Wildlife, State Lands, Land Conservation and Development, and Environmental Quality;

U.S. Army Corps of Engineers;

National Marine Fisheries Service;

U.S. Department of Fish and Wildlife;

Federal Highway Administration (FHWA); and

U.S. Environmental Protection Agency (EPA).

Making a Difference

The National Partnership for Highway Quality ( recognized the Oregon Department of Transportation ( with a Gold level 2010 Making a Difference Award for Partnering ( ODOT received the honor because of strong collaborations with nine environmental regulatory agencies that helped it deliver on its commitment to avoid and minimize impacts as it repairs and replaces hundreds of aging highway bridges statewide.

ODOT’s success in environmental stewardship on the OTIA III State Bridge Delivery Program ( is due largely to early planning and coordination with its regulatory partners to design a programmatic permitting process.

Together, they developed a single set of standards that meets all the contributing agencies’ goals while allowing contractors maximum flexibility in how they achieve them. Many of ODOT’s successes in materials reuse and recycling, stewardship of species and habitats, and protection of water quality are the result of this collaborative, outcome-oriented approach.

ODOT worked with the Oregon Departments of Fish and Wildlife, State Lands, Land Conservation and Development, and Environmental Quality; U.S. Army Corps of Engineers; National Marine Fisheries Service; U.S. Department of Fish and Wildlife; Federal Highway Administration; and U.S. Environmental Protection Agency to streamline the programmatic permitting process. Through this effort, the partners have permitted all eligible projects – a total of 206 bridges – and will ultimately save the agency an estimated $73 million in costs avoided.

“ODOT and its team of partners knew that the only way to tackle this challenge was to work together for a solution,” says Tom Lauer, ODOT major projects branch manager. “The important relationships we’ve built through the bridge program will continue as we extend our commitment to protecting the environment on future transportation projects.”

Award recipients were judged on: their measurement of a high-quality result and customer focus; the originality and ingenuity of innovation; cooperation involved in innovation; implementation of innovation by the respective organization; and cost and time savings.

wireless headsets versus two-way radios for DOT crews From our partners

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