Section 4: Preservation Options
Anchor: #i1003246Overview
Historically significant bridges are addressed under the provisions of Section 4(f) of the Transportation Act of 1966 and may be demolished or moved only if it can be demonstrated that “there is no feasible and prudent alternative” to this taking of the historic property. Options that do not require the demolition of the bridge must be thoroughly considered including the no-build option, as well as construction of the new structure on new location or on a parallel facility. These alternatives need to be examined, evaluated, and thoroughly documented before any decision is made to demolish the bridge or to market it for removal and transport to another location for non-vehicular reuse. Alternatives that keep the bridge in some level of vehicular service must also be examined—that is, rehabilitating the bridge in a way that does not destroy its historic integrity or retaining the historic bridge as part of a one-way pair or as an alternate scenic crossing.
The Federal Highway Administration (FHWA) makes the final determination about whether the conditions of Section 4(f) have been met, that is, whether or not it has been demonstrated that there is no feasible and prudent alternative to the action that will remove and dispose of the historic bridge. Additional cost and additional displacements do not necessarily render an alternative imprudent or infeasible.
Anchor: #i1003261Rehabilitation/Improvement for Continued Vehicular Use
For on-system bridge projects, a deficient historic bridge may remain in regular vehicular service only when it is rehabilitated or improved to meet applicable design standards or a design exception is approved for the deficiency while maintaining its historic integrity to the greatest extent possible.
For off-system bridge projects, some specific geometric, safety, and load capacity criteria for the retention and preservation of historic bridges have been developed and issued. (See the criteria in the next subsection, which is titled Off-System Historically Significant Bridge Projects.) Off-system historic bridges that meet or exceed these minimum criteria may be rehabilitated/improved and remain in vehicular service. Historic bridges that fail to meet the minimum standards should be removed from vehicular service unless an appropriate design exception is approved by the Bridge Division and/or the Design Division for any deficiencies in load carrying capacity, geometry, or safety. For example, if the district applies the criteria and determines that a bridge meets the minimum width criteria but not the loading criteria, the district would not need to apply for a width design exception but would still need to apply for a design exception for loading. Bridges that are unable to safely carry a 3-ton load must be removed from vehicular service until they are rehabilitated or replaced. In rare instances a historic bridge may be reused for vehicular traffic at another location. In this case, the bridge must be suitable for the type and volume of traffic the structure can safely service over its remaining life.
Anchor: #i1003278Off-System Historically Significant Bridge Projects
A TxDOT-administered project for restoration and repair work on a historically significant bridge, that is located on a public road or street not on the designated state highway system may be developed and carried out to raise the condition level of the bridge so it may continue to carry vehicular traffic. Historically significant bridges are those listed or eligible to be listed in the National Register of Historic Places.
Normally these historically significant bridges cannot be cost effectively upgraded to meet the usual design standards for roadway width, load carrying capacity or traffic railing without significantly altering the aspects that make the bridge historically significant. The following table applies to historically significant off-system bridges. Historic off-system bridges that cannot be upgraded to meet or exceed these minimum criteria may be considered for preservation projects on a case by case basis when approved as a design exception.
|
Current Average Daily Traffic (ADT) |
Minimum Clear Roadway Width1 |
Minimum Load-Carrying Capacity (Operating Rating) |
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|---|---|---|---|---|
|
|
One-Lane, Two-Way Operations2 |
Two-Lane, Two-Way Operations |
Alternate Route Available5 |
Alternate Route Not Available |
|
ADT 50 or less |
10 feet (3.0 m) |
18 feet (5.4 m) |
HS 5 |
HS 126 |
|
ADT 51 to 250 |
10 feet (3.0 m) |
18 feet (5.4 m) |
HS 8 |
HS 12 |
|
ADT greater than 250 |
Not applicable3 |
Not applicable4 |
HS 15 |
HS 15 |
|
1 For a minimum roadway length of 50 feet (15 meters) adjacent to the bridge end, roadway crown should match clear width across the structure plus additional width to accommodate guard fence if necessary. 2 One-Lane, Two-Way operations are assumed to allow for sight distance across the entire length of the structure. In cases where sight distance across the length of the structure is not available, the allowable minimum clear roadway width shall be the allowable minimum for Two-Lane, Two-Way operations. 3 For ADT greater than 250, One-Lane, Two-Way operations on a structure are not permissible. 4 For ADT greater than 250, use design standards as appropriate for the class of highway as shown within appropriate sections of this manual. 5 To allow these values, the identified alternate route must add no more than 5 miles (8 kilometers) to a trip for essential services such as school buses, and emergency fire and medical access. All bridges on the identified alternate route must have a minimum load rating of HS 12. Historic bridges which do not meet the state legal load limit shall be posted. 6 HS 12 load rating was selected because it represents a typical minimum value for vehicles essential for educational, medical, and fire suppression services. |
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In addition to the criteria listed in the preceding table, vertical clearance restrictions caused by portal or other bracing on trusses should be carefully evaluated to ensure that they allow passage of essential service vehicles. It may be impossible or impractical to provide a crash-tested rail on the bridge. At a minimum, delineation of obstructions and bridge members at the roadway level should be provided. In addition to any required load limit signs, maintenance of needed warning and traffic control signs become a responsibility of the local government.
Anchor: #i1003300Preservation for Nonvehicular Use
Historic bridges that do not meet the criteria for vehicular use may be preserved for other uses. Preservation options include use for nonvehicular transportation purposes at the existing or relocation site, or use as a historical exhibit or monument at the existing or relocation site.
Preservation for bicycle/pedestrian use or as a historic monument at the existing site may be viable options if the replacement structure’s horizontal alignment can be adjusted to bypass the historic bridge.
For a historic bridge that will be relocated and preserved, a project might include two construction phases. The initial phase may provide for the movement of the historic bridge to a temporary or new permanent site including minimum necessary work to stabilize the structure and prevent further damage or deterioration (see FHWA.pdf). Site development and restoration needed for the adaptive use may be completed in the second phase.