Prior to construction, compliance with Section 106 of the National Historic Preservation Act should have resulted in the identification of "historic properties" subject to possible effect by construction. A "historic property" under the Act is a district, site, building, structure or object included in or eligible for the National Register of Historic Places. Historic buildings and archaeological sites are the best-known kinds of historic properties, but expansive urban and rural districts, landscapes, roads and trails, natural areas of traditional cultural importance, and even highways themselves may be eligible for the Register. Compliance with Section 106 involves consultation with the State Historic Preservation Officer (SHPO), Indian tribes, and other parties, as well as surveys to identify historic properties and determine effects on them. It usually results in a written agreement – either an exchange of letters or a Memorandum of Agreement (MOA) – specifying how any adverse effects will be avoided or mitigated. Measures commonly agreed to include:

• Physical avoidance of properties in construction work
• Realignment and other redesign of projects to avoid or reduce impacts
• Adaptive use of historic buildings, structures and other properties for new purposes consistent with their character
• Relocation or removal of historic buildings and structures from project areas
• Incorporation of historic elements into new design
• Retention of historic setting
• Mitigation of road noise
• Reduction in traffic speeds.
• Retention of historic elevations, lane widths, shoulders and road curvature.
• Avoidance of new visual elements, such as curbing, lighting, or signage, that may detract from historic character.
• Landscaping to preserve rural feeling and association where appropriate.
• Recording/Research, which may include: drawings, photography, records research, and informant interviews, as well as historical, architectural, and archaeological studies
• Placing information kiosks/signage in highly visible areas with roadside turnoffs to provide public access. Use in conjunction with recordation and research.

It is very important to ensure that the terms of agreements resulting from Section 106 review are reflected in construction specifications, contracts, and related documents, and that construction personnel are made aware of the need to comply with such terms.

AASHTO and NCHRP 8-40 sponsored a study in 2001 focusing on "the improvement of existing procedures for evaluating cultural resource significance through the use of information technology." The first phase of the study involved the collection of information on how state DOTs and SHPOs use (or do not use) information technology in making decisions on resource significance. The study made the following findings: [N]

• Most SHPOs and DOTs have not completed a standard set of historic contexts for their states; and, if the contexts exist, they exist only on paper.
• Many SHPOs and DOTs do not have their resource inventories in a computer database.
• There are competing state, regional, and national efforts in terms of computerized cultural resource database development.
• When databases do exist, they were not developed to be used as a tool for evaluating significance. Rather, the majority is used to describe and locate resources on the landscape regardless of whether or not they are listed in or eligible for listing in the National Register.
• The majority of the DOT and SHPO staffs rarely use their databases or historic contexts to evaluate properties to determine their eligibility for the National Register. Rather, they rely on their own personal experiences and knowledge, and those of their cultural resource consultants.
• DOT and SHPO staff are generally not satisfied with the tools that they have to make and justify their decisions on the significance of properties, and they would like to see increased sharing of information and approaches among agencies and states.

The situations described above can complicate the identification and evaluation of properties and reduce the efficiency of historic property studies, and increases costs.

Archaeological sites – that is, physical remains of past human activity, on or in the ground – are among the most common kinds of historic property with which DOTs have to deal. Archaeological sites are valuable for the information they contain, which can be used by archaeologists to reconstruct the past. They also may have cultural significance to Indian tribes and other descendant communities, which may sometimes conflict with the interests of archaeologists. They may also have public interpretive value. The following recommendations have been developed with regard to stewardship of archaeological sites, including the artifacts and other objects they contain, and districts or complexes of archaeological sites in construction areas: [N]

• Utilize covenants and easements to ensure avoidance of physical impact, where possible. Easements may be donated to a third party, which then assumes preservation responsibility. Avoiding impacts in this way not only preserves sites for the future, but can save money that would otherwise be spent on archaeological excavations. For example, by preserving nearly 12 acres of archaeological site within the ADOT right-of-way, it is estimated that ADOT saved $2 million in archaeological costs. The preserved sites are treated with respect in the interests of those who ascribe cultural value to them, and may be available for future archaeological research. ADOT has partnered with the city, county, and several Native American tribes to seek funding that will allow expansion of this preserve and its incorporation into a cultural and natural resource park (a grant application is pending). [N]
• In planning avoidance of impact, be sure to consider more than only direct physical impacts. There is little point in investing to preserve a site from direct impacts if it is only going to be lost to indirect effects such as induced development. Some sites may also be subject to non-physical impacts, such as visual and auditory impacts, if they have cultural or interpretive values that can suffer such impacts.
• In providing for physical impact avoidance, be sure to establish where the edge of the archaeological site is closest to the construction area, and maintain a buffer zone of at least 50 feet between the edge of the construction zone and the edge of the site. Fencing, earthen berms, or other permanent barriers can be used to ensure avoidance in conjunction with a buffer zone.
• Consider adding 12-24 inches of topsoil to "cap" sites by intentional burial. Through consultation with concerned parties, make sure that this approach is generally regarded as appropriate to the kind of site involved. Archaeological and geophysical testing may be necessary prior to capping to assess whether compaction, subsidence, chemical leaching, or other effects may occur.

DOTs have developed a variety of ways to steward cultural resources and historic sites in the course of design and construction:

• Pre-construction surveys indicated that TxDOT's Mission Refugio project would require the exhumation of a number of historic human burials, and plans had been agreed to for handling them. When more burials than anticipated were discovered, TxDOT expanded the scope of its public involvement process and contacted other possible stakeholders, including the Refugio county judge, Refugio government officials, a local history museum, and community members. Many of these stakeholders helped TxDOT identify historic features and artifacts.[N]

• When the Arkansas State Highway and Department of Transportation (AHTD) took on the expansion of a one-lane bridge over the Mulberry River in the Ozark National Forest, they chose to construct a rock retaining wall, made with native stone quarried from near the construction site. Using local stone to build the structure was lower in cost than some traditional systems, and was much cheaper than a masonry face. It also enabled the wall to fit in with the natural surroundings. The team chose a mechanically stabilized earth (MSE) wall system, using geogrid reinforcements for the taller walls, covered by the locally quarried stone. It required no special equipment or labor, and provided more flexibility without distress. AHTD widened the existing gravel road to two travel lanes with shoulders; constructed a bridge over Indian Creek; developed drainage improvements; and designed functional, yet aesthetic, retaining walls for the project. Native stone also provided natural water drainage. Concrete would have enabled water to seep into the walls when the Mulberry River flooded, causing a buildup of hydrostatic pressure through water retention. Retaining walls are now free-draining, eliminating the need for a human-engineered drainage system. [N]

• NHDOT continues to maintain just over 50 covered bridges. Hundreds more used to exist. Old bridges have been carefully rehabilitated under a state law allowing NHDOT to use State Bridge Aid money for this purpose. With an 80 percent share from the state and 20 percent from the town, each new covered bridge is rebuilt to retain its historic character while meeting legal load and height standards. The $3 million Smith Millennium Covered Bridge (Long Truss with integrated arches spans 163 feet over the Baker River in Plymouth) can handle two 18-wheel tractor-trailer trucks passing each other. It combines the historically proven qualities of a wooden covered bridge with more modern amenities, such as a fire detection system, lighting for the interior travel way and an exterior sidewalk. A picture is included to the right. This and other new covered bridges in New Hampshire are the result of state and community partnerships that led to the rebuilding of local landmarks, thus restoring part of the state's heritage that are also highly functional parts of the state's transportation system. They are structures that both honor the past and look to the future. [N]