Developing Geometric Design Criteria and Processes for Nonfreeway RRR Projects
T 5040. 28
October 17, 1988
- PURPOSE . To provide guidance on developing or modifying criteria
for the design of Federal-aid, nonfreeway resurfacing, restoration, or rehabilitation
- CANCELLATION . FHWA Technical Advisory T 5040. 21, Geometric Design
Criteria for Nonfreeway RRR Projects, dated April 4, 1983, is canceled.
- 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.
- 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.
- 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.
- 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
- "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.
- 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.
- 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,
- (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).
- 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.
- 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.
- 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.
- 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.
- 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
- 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.
- 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
- 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
- (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.
- 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) 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.
- 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
- (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
- (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.
- 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
- 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.
- 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
- (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
- DESIGN PRACTICES FOR KEY HIGHWAY FEATURES
- 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
- (b) A second method involves a series of design speeds. This method
requires the determination of the speeds that affect four of the
- 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.
- 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.
- (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
- 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
- (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.
- (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
- (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
- (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
- (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
- (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.
- (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
- (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
- (c) Any paving of the shoulder area should incorporate a pavement
structure capable of supporting anticipated loadings.
- 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.
- 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
- (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.
- 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 DEFICIENCY||ALTERNATE SAFETY MEASURE|
|Narrow lanes and shoulders||Pavement edge lines|
Raised pavement markers
|Roadside hazard markings|
Breakaway safety hardware
|Narrow bridge||Traffic control devices|
|Poor sight distance at hill crest||Traffic control devices|
|Sharp horizontal curve||Traffic control devices|
Pavement antiskid treatment
|Hazardous intersections||Traffic control devices|
Pavement antiskid treatment
- 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|
|10 Percent or More Trucksb
||Less Than 10 Percent Trucksb|
|Combined Lane and Shoulder Widthd (ft)||Lane Widthc|
|Combined Lane and Shoulder Widthd (ft)|
|50 and over
|50 and over
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.
||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
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
- 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,
- 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
- 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,
- Memorandum - "1984 RRR Activities - Summary Report," November
- 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
- Memorandum - "4R Program - Design Exceptions," July 9, 1984.
- Memorandum - "Safety Analysis - Nonfreeway 3R Program," April
- 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 Maintenance Manual," AASHTO, 1976.
- "Maintenance Review Manual," FHWA, 1987.
- "Guide to Safety Features for Local Roads and Streets," FHWA,
- "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,
- 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
- User's Guide - "Local Highway Safety Studies," July 1986.
- User's Guide - "Local Highway Safety Improvement Program," July
- Procedural Guide - "Highway Safety Engineering Studies," FHWA,
- Informational Guide - "Two-Lane Road Cross-Section Design," FHWA,
- Pamphlet - "Roadside Improvements for Local Roads and Streets,"
- Pamphlet - "Improving Guardrail Installations on Local Roads and Streets,"
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."