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Design

Technical Advisory

Developing Geometric Design Criteria and Processes for Nonfreeway RRR Projects

T 5040. 28

October 17, 1988

  1. PURPOSE. To provide guidance on developing or modifying criteria for the design of Federal-aid, nonfreeway resurfacing, restoration, or rehabilitation (RRR) projects.
  2. CANCELLATION. FHWA Technical Advisory T 5040. 21, Geometric Design Criteria for Nonfreeway RRR Projects, dated April 4, 1983, is canceled.
  3. BACKGROUND
    1. Part 625 of Title 23, Code of Federal Regulations (CFR), "Highways" (23 CFR 625), was revised on June 4, 1982 (47 FR 25263, June 10, 1982), to allow greater flexibility and local discretion in the geometric design of nonfreeway RRR projects. Effective July 12, 1982, minimum geometric design criteria for new construction and reconstruction no longer applied to Federal-aid nonfreeway projects unless a State specifically proposed adoption of those criteria for nonfreeway RRR projects. Separate geometric design criteria could be developed and adopted for nonfreeway RRR projects.
    2. Part 625 was further revised on March 24, 1983 (48 FR 13410, March 31, 1983) to comply with subsection 109(o), Title 23, United States Code (U. S. C. ), "Highways" (23 U. S. C. 109(o) ) added by Section 110(a) of the Surface Transportation Assistance Act of 1982.

      This subsection clarifies that federally funded nonfreeway RRR projects shall be constructed to preserve and extend the service life of existing highways and enhance highway safety.

    3. Technical Advisory T 5040. 21, Geometric Design Criteria for Nonfreeway RRR Projects, dated April 4, 1983, was issued to provide guidance relating to 11 factors to be addressed, as a minimum, in the geometric design criteria developed by a State for use on RRR projects.
    4. Part 625 was again revised on April 9, 1985 (50 FR 14914, April 15, 1985), to adopt as policy for geometric design a new publication by The American Association of State Highway and Transportation Officials titled "A Policy on Geometric Design of Highways and Streets." In the implementing memorandum dated April 15, 1985, subject "Implementation of New Design Criteria for Federal-Aid Projects," 13 controlling criteria were identified. Deviation from these criteria required a formal design exception.
    5. "Special Report 214, Designing Safer Roads, Practices for Resurfacing, Restoration, and Rehabilitation," Transportation Research Board (TRB), 1987, was the result of a study on safety cost-effectiveness of highway geometric design standards for RRR projects onexisting Federal-aid highways mandated by the Surface Transportation Assistance Act of 1982. Part 625 was amended on April 25, 1988 (53 FR 15669, May 3, 1988), to add this report, as a guide and reference, to the list of publications for application on Federal-aid projects. The recommendations on design criteria and procedures in Special Report 214 have been incorporated into this Technical Advisory.
  4. PROCEDURES
    1. As used in this Technical Advisory, the term "criteria" as it relates to RRR means either specific design criteria or procedures or a process which establishes geometric design values for individual projects or groups of projects.
    2. Each State may choose one or a combination of the following options:
      • (1) develop and adopt geometric design criteria specifically for nonfreeway RRR projects,
      • (2) adopt and apply current geometric design criteria for new construction (referenced in 23 CFR 625. 4(a) (1) ) to nonfreeway RRR projects, and/or
      • (3) continue to use previously approved geometric design criteria for nonfreeway RRR projects which have been in existing Certification Acceptance or Secondary Road Plan agreements, provided such criteria are consistent with 23 U. S. C. 109(o).
    3. The RRR criteria developed by a State should indicate the types of projects covered. Criteria may be adopted to cover all RRR projects, or RRR projects grouped by geographic region, type of work involved, functional classification, special purpose, or other appropriate manner.
    4. The recommendations and other information contained in TRB Special Report 214 relating to geometric design may be used as the basis for modifying or developing RRR criteria. This document does not contain standards and should not be interpreted as such.
    5. The geometric design criteria developed by each State pursuant to 23 CFR 625 and this Technical Advisory, and approved by the FHWA constitute the standards required by 23 U. S. C. 109(a). If a State elects to apply current criteria for new construction to nonfreeway RRR projects, a letter stating this intention will be sufficient for FHWA approval.
  5. DISCUSSION. The following paragraphs present information on a process for developing RRR programs and individual RRR projects as well as design criteria for individual geometric elements.
    1. Special design criteria adopted for RRR projects should consider overall highway geometry, design of adjacent segments, and expected trends in traffic growth and truck use, such as on the National Network.
      • (1) The criteria adopted by a highway agency, and approved by the FHWA, become the benchmark for evaluation of the design of a RRR project.
      • (2) The RRR design criteria should address, by modification or incorporation, all controlling elements, and may address additional items selected by a highway agency.
        • (a) As indicated in paragraph 3d, 13 geometric elements were established as the controlling criteria for geometric design. The controlling criteria are design speed, lane and shoulder widths, bridge widths, structural capacity, horizontal and vertical alignment, stopping sight distance, grades, cross-slopes, superelevation, and horizontal and vertical clearances.
        • (b) New construction standards apply for those controlling elements not addressed by special RRR criteria.
      • (3) Adoption of RRR criteria for the geometric elements for nonfreeways does not relieve agencies from meeting new construction policies, standards or standard specifications for all nongeometric elements. Deviations substandard to these policies and standards require approval on a project-by- project basis as discussed in paragraph 5a(4).
      • (4) Deviations substandard to the adopted RRR criteria require justification on a project-by-project basis. The documentation justifying the lesser criterion might include, as appropriate and depending on the scope of the project, a discussion of the proposal including alternatives to the proposed action, compatibility of the exception with adjacent sections of roadway and future improvements on the route; a complete description or a sketch showing the design feature and its relation to other roadway elements; a cost analysis; an accident analysis; proposed mitigation measures, if any; the expected safety consequences; and other considerations to support the recommendation to use a design exception.
    2. Paragraph 6, "Safety Conscious Design Process," gives guidance on a systematic approach to developing a program of projects and on a consistent application of key activities for design of individual projects.
      • (1) The purpose of RRR is to preserve and extend the service life of existing highways and enhance highway safety (23 U. S. C. 109(o)).
        • (a) The most current source of data, procedures and recommendations regarding geometric design and its relationship to safety for RRR projects is contained in TRB Special Report 214.
        • (b) The information in Report 214, together with current program guidance and other technical material can be used to develop or modify criteria, processes and practices to achieve the twin objectives of RRR type projects -preservation and safety enhancement.
      • (2) By their purpose and definition, RRR projects reflect and emphasize the management of the highway system by extending the service life and deriving the maximum benefit from existing highways. Economic considerations are a major factor in determining the priority and scope of RRR work.
        • (a) Special geometric design criteria developed for RRR projects should acknowledge this factor and emphasize implementation of cost-effective improvements where practical.
        • (b) Special Report 214 contains economic evaluation procedures for several of the elements included in its recommendations. These evaluation procedures may be used to consider the economic consequences of a proposed improvement.
      • (3) The topics addressed in paragraph 7, "Design Practices for Key Highway Features," include 10 of the 13 controlling criteria as they relate to RRR.
        • (a) The 10 controlling criteria discussed under appropriate headings are design speed, horizontal and vertical alignment, lane and shoulder widths, bridge widths, cross-slope, superelevation, stopping sight distance, and horizontal clearance.
        • (b) The three not addressed here or in the TRB Special Report 214 are vertical clearance, structural capacity, and grades. No new data was available or developed on which to base specific recommendations. However, if these elements are modified by special RRR criteria, special consideration should be given to the size and weight of trucks legally allowed to operate on the affected route.
  6. SAFETY CONSCIOUS DESIGN PROCESS. The RRR program should reflect the needs and objectives of the highway agency in its management of the highway system. Sound pavement management practices, and the need to improve and extend the useful life of the pavement is often the reason for initiating a RRR project. While it may not be the primary reason for initiating a RRR project, highway safety is an essential element of all projects. Federal-aid RRR projects are to be developed in a manner which identifies and incorporates appropriate safety enhancements.
    1. Effective pavement and safety management programs which systematically identify and incorporate needed safety and geometric corrections and enhancements into the project development procedure should be developed and applied.
      • (1) Correction of safety deficiencies and inclusion of appropriate enhancements must be integrated into the design process in the early stages of project identification as well as during each phase of project development.
      • (2) The RRR work often provides an opportunity to incorporate safety improvements into a project in conjunction with the pavement and geometric work. Consideration of the roadway, the roadside andoperational features is required to integrate the safety improvements.
        • (a) Safety improvements can include intersection and access point adjustments that increase sight distance and reduce vehicle conflicts, replacement or rehabilitation of obsolete bridge rails and guardrails, removal of roadside obstacles and unnecessary guardrails, slope flattening, ditch relocation and/or regrading, upgrading roadside appurtenances, new or improved signing, pavement markings and other traffic control devices.
        • (b) Special Report 214 provides information to develop programs and procedures that insure the consideration for safety is included in the initial scope and estimate for a project.
    2. A process that insures that safety is an integral part of project development consists of several critical elements which include:
      • (1) the determination of existing geometric, safety and operational features throughout the project. The designers of RRR projects can draw on a substantial amount of information in the preparation of a design.
        • (a) The information available includes lane and shoulder widths; degree, length and superelevation of horizontal curves; length of vertical curves; stopping sight distances; grades; sideslopes; clear recovery areas; available right-of-way; potentially hazardous obstacles; location and design of intersections; type and location of highway signs; pavement markings; delineation and traffic signals.
        • (b) Line diagrams, strip maps, as-built plans, photologs, etc. are useful sources of information.
      • (2) A procedure to gather and analyze accident, speed and volume data. The analysis of this information can be used to identify specific safety or operational problems and develop appropriate countermeasures.
      • (3) A method to obtain speed data, using generally accepted study procedures, at various locations where they are to be used for design within the project limits for speed dependent design elements. The use of various speed measures is discussed in paragraphs 7a, 7c(1), 7c(2), and 7d(1).
      • (4) A thorough field review by personnel knowledgeable about and trained in design, safety, traffic operations and maintenance to identify potentially hazardous locations and features, and recommend appropriate safety enhancements. Field reviews are also beneficial to verify existing conditions and identify recent changes.
      • (5) Consideration and incorporation, as appropriate, of high hazard locations, intersection, roadside and traffic control improvements that may result in enhanced safety. There are many relatively low-cost improvements that can be highly cost effective when incorporated into certain RRR projects. Paragraph 7h discusses alternate safety improvements.
      • (6) A procedure for routine review of projects during development by traffic and safety specialists. This should include periodic consultation with these specialists before final approval of the project plans.
    3. A systematic process to accomplish the above data and information collection and analysis involves a series ofactivities which can culminate in a design and safety report.
      • (1) This report can serve as documentation of the design process undertaken to develop the RRR project, assist in design decisions and provide the background information needed to obtain any necessary design approvals.
        • (a) The components which should be incorporated in the report include the existing and proposed geometric and roadside features, current and estimated future traffic volumes, speeds, accident history, applicable design standards and design options.
        • (b) Specific safety problems or concerns should be identified and addressed along with options, costs and recommendations to alleviate the problem.
        • (c) Any identified design exceptions (geometric and nongeometric) and appropriate mitigations should also be included in this report.
      • (2) While neither a format nor a length for this report is specified, it should be as detailed as the size, scope, and complexity of the project requires. A simple form summarizing the information may be sufficient for many projects, while a detailed report may be necessary for more complex projects or in situations where accident and traffic histories warrant consideration.
    4. Desirable geometric and safety improvements are frequently dependent upon acquisition of right-of-way. Although right-of-way acquisition problems are a concern, adverse social, environmental, or economic impacts on the surrounding land and development also often limit the scope of improvements.
      • (1) These problems are evident in those locales with significant adjacent development or where existing right-of-way for the highway is narrow. These factors are frequently the cause for delay in advancing the project to construction.
      • (2) These potential conflicts should be taken into account early in the RRR process. A process to screen candidate projects to identify locationswhere improvements are desirable and require right-of-way should be instituted.
        • (a) With these locations identified, the design at these sites can be expedited to determine the actual right-of-way requirements. Using timesaving techniques, the acquisition of the necessary real estate for the project can be expedited to insure its availability in time for construction.
        • (b) A process can be instituted to work in advance with affected parties to identify environmental and community impacts in order to develop an acceptable balance between community concerns and project needs.
    5. Whenever possible, RRR projects should include other anticipated work in or adjacent to the project area. While the need for RRR and other type improvements may originate from separate and distinct processes for identifying deficiencies, they should be coordinated, as the implementation of projects in one area of concern may influence priorities in another. Experience indicates that cost savings may be achieved and needless duplication of construction and traffic disruption can be avoided when separate projects in the same area are combined into a single contract.
    6. Consistency of roadway, roadside, and operational design is an essential element for assuring safe and appropriate driver responses. Drivers associate andexpect certain features and conditions for each category of highway. Improving the consistency of design within each category helps to satisfy driver expectations and reduce the possibilities of driver confusion.
      • (1) Highway agencies are encouraged to perform a periodic assessment of the potential for systemwide, route, or route section safety upgrading design in connection with or in addition to programs to identify and correct specific hazardous locations.
      • (2) These periodic assessments of improvements on the basis of one of the preceding classifications can increase the positive impact of RRR projects on safety in several ways.
        • (a) The results could be used to help tailor design practices and standards to the circumstances of a particular highway agency.
        • (b) The results could detect opportunities for effective safety improvements that warrant project programming earlier than previously anticipated.
        • (c) The assessment could be linked to other safety programs to gauge overall progress toward improving highway safety.
        • (d) Along with the results of other analyses, the assessments could serve as input for establishing future highway programs and funding requirements.
  7. DESIGN PRACTICES FOR KEY HIGHWAY FEATURES
    1. Design Speed. Vehicle speed is an essential parameter for a number of geometric criteria. A design speed is selected to correlate the various design elements. The definition of design speed is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features govern. It is important that any speed selected as the design speed for a project realistically reflect the speeds at which vehicles can be expected to operate or are actually operated on the highway.
      • (1) There are two methods that can be used to select the design speed for a RRR project. These procedures may be used alone or in combination. In either case, the objective is to coordinate the various geometric elements to produce a safe highway.
        • (a) One method is to select an overall project design speed. This is defined as the speed that equals or exceeds the posted or regulatory speed on the section of highway being improved. All the various geometric elements on the project are correlated by this one design speed.
        • (b) A second method involves a series of design speeds. This method requires the determination of the speeds that affect four of the individual elements.
          • 1 The average running speed throughout the project length may be used as the design speed in determining lane and shoulder widths. The average running speed is the average speed of a vehicle over a specified section of highway.
          • 2 The 85th percentile speed may be used for horizontal and vertical curves. The 85th percentile speed is the speed below which 85 percent of the vehicles are operating.
        • (c) The specific applications of these speeds are discussed in paragraphs 7c(1), 7c(2), and 7d(1).
      • (2) When a speed less than the posted or regulatory speed is used, speed studies using generally accepted study procedures are required to establish the speed at each location where the average running or 85th percentile speed is to be applied. The results of these studies are to be used as the basis for determining the design speed for the element whether the posted or regulatory speed is exceeded or not.
    2. Traffic Volumes. Traffic data is needed in the design of all highway improvements, including RRR. It is an important consideration both in the determination of the appropriate level of improvement (i. e., reconstruction vs. RRR) and in the selection of actual values for the various geometric features.
      • (1) Design decisions for particular highway features should be based on conditions that reflect the anticipated service life of the feature even though the expected performance period of the pavement rehabilitation work may be much less than the performance period for geometric improvements.
        • (a) For RRR, the need for a formal forecast of future traffic is the greatest when the current traffic is approaching the capacity of the highway, and decisions must be made regarding the timing of major improvements such as additional lanes.
        • (b) Studies to determine future traffic are not normally necessary on very low-volume roads where even high-percentage increases in traffic do not significantly impact design decisions.
      • (2) Preferably, the design traffic volume for a given feature should match the average traffic anticipated over the service life of the affected feature such as alignment and widths.
    3. Alignment
      • (1) Horizontal Curves
        • (a) An existing horizontal curve may be retained as is without further evaluation if:
          • 1 the existing curve design, assuming correct superelevation is provided, corresponds to a speed that is within 15miles per hour (mph) of the 85th percentile speed of the approaching vehicles; or within 15 mph of the overall project design speed, and
          • 2 the design volume is less than 750 vehicles per day.
        • (b) Reconstruction to either new construction standards or to approved RRR standards is to be considered and evaluated when the above speed and/or volume criteria are exceeded.
        • (c) If the curve reconstruction is not justified, or if it is reconstructed to less than new construction standards, appropriate safety and other mitigation measures should be applied. Safety measures that are less costly than reconstruction include, but are not limited to, those enumerated in paragraph 7h(2). These measures may be applied either separately or in combination.
        • (d) The 85th percentile speed, defined in paragraph 7a(1) (b) 2, is to be measured at a point ahead of each end of the curve where vehicle operators have not begun adjusting their speed. Project design speed is as defined in paragraph 7a(1) (a).
      • (2) Vertical Curves
        • (a) An existing vertical curve may be retained as is, without further evaluation if:
          • 1 the existing curve design speed, based on the stopping sight distance provided, corresponds to a speed that is within 20 mph of the 85th percentile speed of vehicles on the crest, or within 20 mph of the overall project design speed; and
          • 2 the design volume is less than 1,500 vehicles per day.
        • (b) Reconstruction of crest vertical curves to either new construction standards or to approved RRR standards is to be evaluated when the above speed and/or volume criteria are exceeded, and the vertical curve hides major hazards from view.
        • (c) Whether or not an evaluation is required, designers should routinely examine the nature of potential hazards such as intersections, sharp horizontal curves, or narrow bridges hidden by a vertical curve, their location in relation to the portion of the highway where sight distance falls below new construction standards, and other options to reconstruction such as relocating or correcting the hazard or providing warning signs.
        • (d) If curve reconstruction is not justified, or the curve is reconstructed to less than new construction standards, appropriate safety and other mitigation measures should be applied. Safety measures that are less costly than reconstruction include, but are not limited to, those identified in paragraph 7h(2). These measures may be applied separately or in combination.
        • (e) The 85th percentile speed, defined in paragraph 7a(1) (b) 2, is to be measured on the crest of individual vertical curves for vehicles traveling in both directions. Project design speed is as defined in paragraph 7a(1) (a).
        • (f) While the preceding discussion focused on crest vertical curves, sag verticals should not be ignored. Substandard sag vertical curvesshould be investigated to insure that potential hazards do not exist, especially ones that become apparent when weather conditions or nighttime reduces visibility.
      • (3) Curves in Series. Frequently the alignment of a segment of a roadway consists of a series of reverse curves or curves connected by short tangents. A succession of curves may be analyzed as a unit rather than as individual curves, applying the criteria in paragraphs 7c(1) and 7c(2) as appropriate.
        • (a) The first substandard curve in a series should receive special attention because this change in alignment prepares the driver for the remaining curves in the series.
        • (b) Any intermediate curve in a series of substandard curves that is significantly worse than the others in the series should also be analyzed individually.
        • (c) These controlling curves can be used to determine the safety and/or other mitigation measures to apply throughout the series.
        • (d) When improvements are considered to any curve in a series, the effect on the series of curves as a whole should be evaluated.
    4. Cross-Section
      • (1) Lane and Shoulder Widths. Wide lanes and shoulders provide motorists increased lateral separation between overtaking and meeting vehicles and an opportunity for safe recovery when their vehicles run off the road. Additional safety benefits include reduced interruption of the traffic flow as the result of emergency stopping and road maintenance activities, less pavement and shoulder damage at the lane edge, improved sight distance at critical horizontal curves, and improved roadway surface drainage.
        • (a) Suggested minimum lane widths and combined lane and shoulder widths are provided in Table 1 of Attachment 1. The suggested minimums explicitly consider vehicle speed and the amount of truck traffic, which influence the safety benefits derived from wider lanes and shoulders.
        • (b) Either of the two methods may be used as the speed parameter for determination of appropriate lane and shoulder widths.
          • 1 Average running speed throughout the project length is one method. This speed is defined in paragraph 7a(1) (b) 1.
          • 2 The overall project design speed is the second method that may be used. Design speed is defined in paragraph 7a(1) (a).
      • (2) Bridge Widths. Hazards associated with bridge widths can be significant. Roadway constriction at narrow bridges reduces the opportunity for safe recovery of out-of-control vehicles and can result in end-of-bridge collisions. Furthermore, bridge approaches are often on a downgrade, a factor responsible for increases in speed, and particularly in the case of older spans, are often sharply curved. When coupled with other factors such as premature icing in winter and substandard bridge rail, the special hazards associated with bridges are readily understood.
        • (a) An existing bridge may be retained when the suggested bridge widths in Table 2 of Attachment 1 exist.
        • (b) A bridge should be evaluated for replacement or widening on a case-by-case basis when the criteria suggested in Table 2 are not met.
        • (c) Safety at narrow bridges can also be improved by transition guardrails at bridge approaches, new or rehabilitated bridge rails and warning devices.
          • 1 If an existing bridge is to be retained, substandard bridge rail should be upgraded to current standards and "safety" curbs which can cause vehicles to vault the rail should be eliminated. Exceptions may be considered on a case-by-case basis where safety can be adequately enhanced but cost effective considerations prevent full widening or full upgrading of the bridge rail.
          • 2 On all projects involving bridges, the approach guardrail should be evaluated and upgraded to current standards. Approach guardrail must be properly anchored to the bridge.
          • 3 The transition between the approach guardrail and the bridge rail should be smooth and of sufficient strength (i. e., reduced post spacing) to prevent snags and vehicle pocketing.
          • 4 Only approved crash-tested bridge rails, guardrail, and transitions should be used.
          • 5 A partial list of alternate safety measures is identified in paragraph 7h(2).
      • (3) Cross-Slope and Superelevation
        • (a) On RRR projects that include resurfacing, pavement cross-slopes should be restored to new construction standards.
        • (b) Superelevation rates on horizontal curves should be increased, if necessary, to the appropriate rate for new construction for the design speed being used at the location.
      • (4) Roadside Features. Accident data firmly establish that roadside characteristics are important in determining the overall level of safety provided by a highway. Accident rates are lower and accidents are less severe on highways with few obstacles near the travelway.
        • (a) Consistent procedures should be developed for evaluating and improving roadside features with the following objectives:
          • 1 Remove, relocate, shield, or reconstruct to a breakaway design isolated roadside obstacles.
          • 2 Flatten sideslopes that are 3:1 or steeper at locations where run-off-road accidents are likely to occur (e. g., on the outside of sharp horizontal curves).
          • 3 Retain current slope ratios (i. e., do not steepen sideslopes) when widening lanes and shoulders unless warranted by special circumstances.
        • (b) Clear zone policies can be tailored to particular types of obstacles commonly encountered by a highway agency to reflect differences in the cost of removal, relocation, or shielding.
    5. Pavement
      • (1) The existing pavement condition and the scope of needed pavement improvements dictate to a large extent those improvements which are feasible, prudent, or practical. More significant geometric upgrading might be appropriate if the pavement improvements are substantial, but may not be appropriate or economical if needed pavement work is relatively minor. Conversely, the geometric deficiencies may be so severe that the overall highway improvements must be more substantial than those which may be appropriate with only minor pavement improvements.
        • (a) Geometric design criteria should indicate how existing pavement condition and the scope of pavement improvements will interrelate with the scope of geometric improvements and the values used for design.
        • (b) Pavement rehabilitation is to be developed in accordance with current FHWA pavement policy.
      • (2) A skid resistant surface is an essential part of any pavement surface improvement, regardless of the scope of geometric problems or upgrading. Current policy requires that each Federal-aid project, including RRR projects, involving pavement construction shall provide a skid resistant surface.
      • (3) Pavement edge drops are undesirable, no matter how they develop, because of the safety implicationsassociated with the vehicle recovery maneuver. Pavement edge drops, defined as vertical discontinuities at the edge of the paved surface, often develop between the pavement surface and the adjacent unpaved shoulder or roadside. They can result from adding a layer of surfacing without regrading the existing shoulder; wear or erosion of gravel, turf, or earth shoulder materials.
        • (a) Properly designed and constructed RRR projects can reduce edge drop related accidents. Existing policy requires that edge drops be eliminated on Federal-aid projects. Any RRR criteria developed should include procedures and practices to eliminate designs and construction operations which lead to creation of edge drops, and that reduce their occurrence along existing highways.
        • (b) There are several practices which can reduce the occurrence or mitigate the impact of edge drops. These practices include:
          • 1 paving the full top width between shoulder breaks;
          • 2 selectively paving shoulders at points where vehicle encroachments are likely to create pavement edge drops, such as on the inside of horizontal curves; or
          • 3 constructing a beveled or tapered pavement edge so that any edge drop that develops has a reduced impact on the recovery maneuver.
        • (c) Any paving of the shoulder area should incorporate a pavement structure capable of supporting anticipated loadings.
    6. Intersections. Intersections deserve special attention, since accidents tend to concentrate at these locations.
      • (1) Although specific guidelines for intersection improvements are not appropriate because of the wide variety of physical and operational features affecting safety, it is recommended that consistent procedures and checklists be developed for evaluating intersection improvements on RRR projects.
      • (2) Intersection improvements should be tailored to each individual situation with due recognition being given to traffic volumes on each of the intersecting roadways, prior accident pattern and physical characteristics of the site.
        • (a) The improvements at intersections generally focus on reducing conflicts and improving driver guidance. Reducing approach speed and improving skid resistance can be important also.
        • (b) There are several useful analysis procedures available to assist in selecting safety improvements, including collision diagrams, condition diagrams, and a field review of the intersection.
    7. Traffic Controls and Regulations
      • (1) Signs and markings in conformance with the Manual on Uniform Traffic Control Devices (MUTCD) are required on all federally funded highway projects, including RRR.
      • (2) While traffic control devices cannot fully mitigate all problems associated with substandard geometric features, they are a relatively low-cost measure that can compensate for certain operational deficiencies.
        • (a) Where roadway geometry or other roadway or roadside features are less than standard, do not meet the driver's expectancy, and reconstruction is not appropriate, additional signs, markings, delineation, and other devices beyond normal requirements of the MUTCD should be considered.
        • (b) Judicious use of special traffic regulations, positive guidance techniques and traffic operational improvements can often forestall expensive reconstruction by minimizing or eliminating adverse safety and operational features on or along existing highways.
    8. Alternate Safety Measures
      • (1) Highway design practice provides a broad range of alternative measures that can be used alone or in combination with others to mitigate the effects of geometric deficiencies and provide for safer operations on existing highways.
      • (2) A partial list of alternatives to reconstruction for several geometric deficiencies is provided in the following table.

        GEOMETRIC DEFICIENCYALTERNATE SAFETY MEASURE
        Narrow lanes and shouldersPavement edge lines
        Raised pavement markers
        Post delineators
        Steep sideslopes;
        roadside obstacles
        Roadside hazard markings
        Slope flattening
        Round ditches
        Obstacle removal
        Breakaway safety hardware
        Guardrail
        Narrow bridgeTraffic control devices
        Approach guardrail
        Hazard markers
        Pavement markings
        Poor sight distance at hill crestTraffic control devices
        Fixed-hazard removal
        Shoulder widening
        Driveway relocation
        Sharp horizontal curveTraffic control devices
        Shoulder widening
        Appropriate superelevation
        Slope flattening
        Pavement antiskid treatment
        Obstacle removal
        Obstacle shielding
        Hazardous intersectionsTraffic control devices
        Traffic signalization
        Fixed lighting
        Pavement antiskid treatment
        Speed controls
  8. ATTACHMENT. Attachment 2 to this Technical Advisory is a list of program guidance memoranda, Technical Material, and Training Courses that have been identified as being related to activities concerning RRR type projects.

Thomas O. Willett, Director
Office of Engineering

Table 11 Land And Shoulder Widths
Design Year Volume
(ADT)
Running Speeda
(mph)
10 Percent or More Trucksb Less Than 10 Percent Trucksb
Lane Widthc
(ft)
Combined Lane and Shoulder Widthd (ft)Lane Widthc
(ft)
Combined Lane and Shoulder Widthd (ft)
1-750 Under 50 10 12 9 11
50 and over 10 12 10 12
751-2000 Under 50 11 13 10 12
50 and over 12 15 11 14
Over 2000 All 12 18 11 17

a Highway segments should be classified as "under 50" only if most vehicles have an average speed of less than 50 mph over the length of the segment.

b For this comparison, trucks are defined as heavy vehicles with six or more tires.

c If the highway is included on the National Network or is an access road for the network, a 12-foot lane width should be used.

d One foot less for highways on mountainous terrain.


Table 21 Bridge Widths
Design Year Volume (ADT) Usable Bridge Width(ft)
0 - 750 Width of approach lanes
751 - 2000 Width of approach lanes plus 2 ft.
2001 - 4000 Width of approach lanes plus 4 ft.
Over 4000 Width of approach lanes plus 6 ft.

If lane widening is planned as part of the RRR project, the usable bridge width should be compared with the planned width of the approaches after they are widened.

1 From Special Report 214, "Designing Safer Roads, Practices for Resurfacing, Restoration, and Rehabilitation," TRB 1987.

Program Guidance :

  • Code of Federal Regulations Title 23, "Highways," Part 625, "Design Standards for Highways."
  • Code of Federal Regulations Title 23, "Highways," Part 626, "Pavement Design Policy."
  • Federal-aid Highway Program Manual 6-2-1-1, "Design Standards for Highways."
  • Federal-aid Highway Program Manual 6-2-4-1, "Pavement Design Policy."
  • Memorandum - "Design Exceptions on Routes Legally Available to Larger Vehicles Authorized by STAA of 1982," June 22, 1988.
  • Memorandum - "Design Monitoring 1986 Summary Report," June 26, 1987.
  • Memorandum - "Guidelines for Mitigating Dropoffs in Construction and Maintenance Work Zones," December 1, 1986.
  • Memorandum - "Preservation of Roadside Safety," October 10, 1986.
  • Memorandum - "Bridge Rails," August 28, 1986.
  • Memorandum - "Accident Reduction Factors," July 21, 1986.
  • Memorandum - "Design Approval for Federal-aid Projects," July 10, 1986.
  • Memorandum - "Accident Reduction Factors," November 8, 1985.
  • Memorandum - "Design Speed," August 21, 1985.
  • Memorandum - "Implementation of New Design Criteria for Federal-aid Projects," April 15, 1985.
  • Memorandum - "3R Program Reviews - Summary Report," February 26, 1985.
  • Memorandum - "1984 RRR Activities - Summary Report," November 14, 1984.
  • Memorandum - "Treatment of Existing Bridges on Federal-aid Projects," October 29, 1984.
  • Memorandum - "Cost-Effective Safety Improvements on Low-Volume Roads," October 4, 1984.
  • Memorandum - "Safety Enhancement - Nonfreeway 3R Program," August 27, 1984.
  • Memorandum - "4R Program - Design Exceptions," July 9, 1984.
  • Memorandum - "Safety Analysis - Nonfreeway 3R Program," April 6, 1984.
  • Memorandum - "Current Policy on Bridge Widths," January 31, 1984.
  • Memorandum - "Final Report - RRR Field Reviews Implementation," January 25, 1984.
  • Memorandum - "3R and Safety Enhancements," September 6, 1983.
  • Memorandum - "Accident Reduction Levels Which May Be Attainable from Various Safety Improvements," August 17, 1982.

Technical Material :

  • Special Report 214, "Designing Safer Roads, Practices for Resurfacing, Restoration, and Rehabilitation," TRB, 1987.
  • State of the Art Report 6, "Relationships Between Safety and Key Highway Features," TRB, 1987.
  • "A Policy on Geometric Design of Highways and Streets," AASHTO 1984 (Green Book).
  • "A Guide for Erecting Mailboxes on Highways," AASHTO, May 1984.
  • "A Guide for Enhancement of Highway Safety Directed to Agencies, Programs, and Standards," AASHTO, 1983.
  • "Guide for Selecting, Locating, and Designing Traffic Barriers," AASHTO, 1977.
  • "AASHTO Maintenance Manual," AASHTO, 1976.
  • "Maintenance Review Manual," FHWA, 1987.
  • "Guide to Safety Features for Local Roads and Streets," FHWA, 1986.
  • "Highway Pavement Distress Identification Manual," FHWA, 1986.
  • "The Flexibility Document," FHWA, April 1986.
  • "Traffic Control Devices Handbook," FHWA, 1983.
  • Publication No. FHWA/RD-87/094 - "Safety Cost-Effectiveness of Incremental Changes in Cross-Section Design - Informational Report," FHWA, December 1987 (Scheduled for publication in July 1988).
  • Report No. FHWA/RD-87/008 - "Safety Effects of Cross-Section Design for Two-Lane Roads, Volume 1 - Final Report," FHWA, October 1987.
  • Report No. FHWA/RD-87/009 - "Safety Effects of Cross-Section Design for Two-Lane Roads, Volume 2 - Appendixes," FHWA, June 1987.
  • Report No. FHWA-IP-86-17 - "Guide to Management of Roadside Trees," FHWA, December 1986.
  • Report No. FHWA-TS-81-216 - "Functional Requirements for Highway Safety Features," FHWA, January 1983.
  • Report No. FHWA-TS-82-232 - "Synthesis of Safety Research Related to Traffic Control and Roadway Elements, Vol. 1," FHWA, 1982.
  • Report No. FHWA-TS-82-233 - "Synthesis of Safety Research Related to Traffic Control and Roadway Elements, Vol. 2," FHWA, 1982.
  • Report No. FHWA-TO-80-2 - "Planning and Field Data Collection," FHWA, December 1982.
  • Report No. FHWA-TO-81-1 - "A User's Guide to Positive Guidance (2nd Edition), " FHWA, December 1981.
  • Report No. FHWA-TS-81-219 - "Highway Safety Evaluations," FHWA, November 1981.
  • Technology Sharing Report 80-228 - "Safety Design and Operational Practices for Streets and Highways," FHWA, May 1980.
  • User's Manual - "Highway Safety Improvement Program," January 1981.
  • User's Guide - "Local Highway Safety Studies," July 1986.
  • User's Guide - "Local Highway Safety Improvement Program," July 1986.
  • Procedural Guide - "Highway Safety Engineering Studies," FHWA, June 1981.
  • Informational Guide - "Two-Lane Road Cross-Section Design," FHWA, June 1987.
  • Pamphlet - "Roadside Improvements for Local Roads and Streets," October 1986.
  • Pamphlet - "Improving Guardrail Installations on Local Roads and Streets," January 1986.

Training Courses (Active) :

  • "Highway Safety Engineering Studies."
  • "Local Highway Safety Studies."
  • "Local Highway Safety Improvement Program."
  • "Safety Features for Local Roads and Streets."
  • "Functional Requirements for Highway Safety Features."
  • "Selecting, Locating, and Designing Traffic Barriers."
  • "Design and Operation of Work Zone Traffic Control."
  • "Human Factors in Design and Operation."
Updated: 09/16/2014
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