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Performance-Based Analysis of Geometric Design of Highways 1

and Streets 2

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Brian L. Ray, P.E. (corresponding author) 6

Kittelson & Associates, Inc. 7

610 SW Alder Street, Suite 700 8

Portland, OR 97205 9

PHONE: (503) 228-5230 10

FAX: (503) 273-8169 11

EMAIL: [email protected] 12

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Erin M. Ferguson, P.E. 14


155 Grand Avenue, Suite 900 16

Oakland, CA 94612 17

PHONE: (510) 433-8066 18

FAX: (510) 839-0871 19


21

Julia K. Knudsen, P.E. 22


610 SW Alder Street, Suite 700 24

Portland, OR 97205 25

PHONE: (503) 228-5230 26

FAX: (503) 273-8169 27


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SUBMISSION DATE: November 8, 2014 39

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WORD COUNT: 5858 41

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NUMBER OF EXHIBITS: 6 = 1500 words 43

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TOTAL WORD COUNT (including 250 words per exhibit): 7358 45

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mailto:[email protected]



Ray, Ferguson and Knudsen 2

ABSTRACT 1

NCHRP Research Project 15-34A: Performance-Based Analysis of Geometric Design of Highways and 2

Streets (now published as NCHRP Report 785) documented a process framework for conducting 3

performance-based analyses of highway geometric design. The performance-based approach supports 4

project documentation needs and can, overall, inform and guide project decision making while supporting 5

risk management objectives. This methodology is based on first, understanding intended project outcomes, 6

and then subsequently considering and selecting geometric design elements or features that best meet a 7

project’s unique context. A performance-based approach gives primary consideration to the respective 8

stage of the project development process, and provides complimentary focus on the performance effects of 9

resulting geometric design decisions. The process framework considers performance factors for particular 10

geometric design elements. This paper encourages designers to consider and select design values or 11

features based on feature’s impact and the role and relationship resultant geometric design performance has 12

on intended outcomes. Specifically, the framework provides an approach for understanding the desired 13

outcomes of a project, selecting performance categories and performance measures that align with those 14

outcomes, evaluating the impact of alternative geometric design decisions on those performance measures, 15

and arriving at solutions that achieve the overall desired project outcomes. 16

17


Introduction 1

Transportation planners and designers can benefit from a framework and methodology to support their 2

highway and street geometric design choices. This applies whether professionals are developing highway 3

and street geometric solutions applying full standards or making design choices resulting in dimensions 4

deviating from typical values. Increasingly, it is no longer fiscally sustainable or, in some circumstances, 5

desirable to categorically construct highways and/or streets to meet full design standards. Initiatives and 6

policies supporting context sensitive solutions, such as “flexibility in highway design”, “practical design” 7

and “complete streets” have revealed the need for roadway planners, designers, and traffic engineers to 8

expand how they approach design solutions. In some project conditions designers are challenged to 9

recommend three-dimensional design guidance where standard dimensions and values may not be 10

attainable. In conditions where “full” design standards and specifications could be applied, design manuals 11

and guidelines often do not provide sufficient specific information about a given condition; and designers 12

must apply their judgment making decisions about highway and street geometric design. Methods to 13

support design decisions will aid professionals in developing solutions best meeting the widest range of 14

contextual design environments. 15

Historically, roadway geometric designers have applied design standards as the means of determining 16

design dimensional values. A common motivation in achieving full standards is to achieve a desired level 17

of safety performance (reduced crash frequency and severity). There is an increasing awareness in our 18

profession that simply applying standards does not necessarily yield a facility with the least likely 19

frequency or severity of crashes. Standards themselves may not be based on objective research that leads 20

to the fewest and least severe crashes. In some cases, geometric design elements and values are based on 21

relatively simple, physics-based models (such as the point-mass model for horizontal curve design). In 22

other cases, the origin of common design values may not be fully documented (such as the technical origin 23

of a 12 foot-wide lane). Geometric designers employ judgment in combining a variety of horizontal, 24

vertical, and cross sectional elements; sometimes within complex or constrained environments. Attaining 25

the values of a policy, standard, code, or guideline may not necessarily result in desired operations or safety 26

performance. 27

New philosophies about fire safety during the 1970s brought a shift in thinking from the traditional 28

“complies with the code/does not comply with the code” approach to a “systems” approach for evaluating 29

and designing system (1). Similar changes in the state of knowledge and the evolution of seismic design 30

led to changes in engineering practice and research in structural engineering. With an emphasis on 31

providing stakeholders the information needed to make rational business or safety-related decisions, 32

seismic engineering moved toward predictive methods for assessing potential (seismic) performance. 33

Engineers recognized code-based strength and ductility requirements applicable for designing new 34

buildings was not always suitable for evaluating and upgrading existing buildings. This resulted in 35

performance-based engineering methods in seismic/structural design. (2). Performance-based approaches 36

have come to the geometric design of highways and streets. 37

The National Cooperative Highway Research Program (NCHRP) Report 785: Performance-Based Analysis 38

of Geometric Design of Highways and Streets presents an approach for integrating performance-based 39

analysis into the geometric design of highways and streets (3). The report is a resource for practitioners 40

planning, designing, maintaining and operating surface transportation facilities; specifically roadways, 41

intersections, interchanges and the supporting features to serve various motorized and non-motorized users. 42

It creates a framework for identifying the desired outcomes for a given project. This includes selecting 43

performance categories and measures reflecting the desired project outcomes. It provides a framework for 44

considering and evaluating geometric design decisions to determine the degree to which these decisions 45

support the intended outcome for the overall project. 46

Incorporating performance-based analysis into the roadway geometric design project development is a 47

critical step forward from historical nominal dimension-based approaches. It enables practitioners to make 48

informed decisions about the performance tradeoffs often encountered in fiscally and physically 49

constrained environments. Agencies across the United States are challenged with limited resources and 50


many demands on those resources. The performance-based analysis framework in NCHRP Report 785 will 1

help practitioners develop solutions to: 1) facilitate travel by walking, biking and transit in addition to 2

passenger cars; 2) reduce crash frequency and severity; 3) support objectives to enhance a community’s 3

livability; 4) support economic development objectives; and 5) support other context sensitive and practical 4

design considerations and approaches. In summary, the framework helps users develop and evaluate 5

highway and street geometric design choices within each unique contextual design environment. 6

The Evolution of Geometric Design of Highways and Streets 7

At the turn of the 19th century, modern cities developed brick or macadam surfaces to counter dust and 8

mud. Rural roadways were primarily established to support passage of horses, wagons, walkers, and 9

bicycles. Roadways originated from trails and paths between communities and to serve farm and ranch to 10

market travel (4). The automobile was in its early development stage and roadways were not specifically 11

adapted to automobile use. For the most part, roadway work focused on improving travel conditions; 12

especially features and elements affected by weather. 13

Automobile ownership developed and expanded into the 1920s. Mechanized transport became more 14

popular in moving people and goods. Former wagon roads were adapted for motorized travel with little 15

change to the locations and alignments or the geometrics (4). Local governments were dominant and there 16

was no national standard. The alignments and grades to serve slower moving, horse drawn carriages were 17

generally maintained. Slow operating speeds meant vertical curves and alignment design was essentially 18

non-existent as drivers could readily negotiate grade changes (5). It became apparent during this period 19

motorized travel’s increasing operating speeds and different vehicle loadings were not conducive to the 20

adapted roadways. 21

With each local entity developing its own roadway configurations, the Committee on Standards of the 22

American Association of State Highway Officials (AASHO) was formed in 1914. The committee initially 23

disseminated information on design among its members and it did not develop national roadway design 24

standards (5). As automobile use expanded in the 1920s and into the 1930s (the “Dawn of the Motor 25

Highway”), new design features and characteristics were integrated to serve higher speed travel (4). These 26

design features included considering sight distance, horizontal and vertical curvature, and superelevation. 27

The principles of railroad design were applied to roadway design. With increased traffic, roadways were 28

configured to serve continuous two way traffic and pavement widths were becoming more consistent. In 29

1928, AASHO recommended the first set of standards to be used by states in guiding roadway design and 30

construction (5). The emphasis remained focused on design consistency between states and not explicitly 31

operational performance. 32

By the late 1930s there were efforts to establish a consistent set of roadway design criteria to address 33

continued concern about inconsistent design policies and practices across the country. AASHO established 34

a Committee on Planning and Design Policies. The committee established a concept of designing roadways 35

based on the expected traffic volumes and vehicle types. AASHO’s 1938 Policy on Highway Classification 36

(6) addressed issues of increasing operating speeds (where drivers did not adequately recognize impending 37

alignment changes) by considering design speed for roadway design. Designing for a selected speed 38

addressed the continued increase in operating speeds and the expectation of its increase would continue in 39

the future (5). Considering design speed implied a recognition and intention of an anticipated performance 40

associated with various horizontal curve radii. 41

AASHO published a variety of design policy brochures in the 1940s to develop design standards among the 42

states. A key emphasis was standardizing nominal values for consistency between states. A Policy on Sight 43

Distance for Highways (7) addressed sight distance dimensions for vertical and horizontal alignments. 44

Increasing crashes associated with passing on two and three lane roads led to a uniform approaching for 45

delineating no-passing zones where sight distance was insufficient. These criteria were published in A 46

Policy on Criteria for Marking and Signing No-Passing Zones on Two- and Three-Lane Roads (8). 47

Subsequent brochures presented policies on a variety of topics with an emphasis on establishing 48

consistency between states not necessarily performance. These brochures included: 49


A Policy on Highway Types (Geometric) in 1940 1

A Policy on Intersections at Grade in 1940 2

A Policy on Rotary Intersections in 1941 3

A policy on Grade Separations for Intersecting Highways, in 1944 4

By 1945, AASHO published A Policy on Design Standards. The policy contained recommended standards 5

from Feeder Roads to the Interstate System (8). The standards generally included condensed and 6

summarized criteria from previous AASHO publications (5). The 1945 document help set the stage for the 7

United States Congress to authorize the Interstate and Defense Highway system (although funding was not 8

provided until 1956). As with previous publications, the primary emphasis was consistency in road building 9

for various facilities across the United States. 10

By 1954 AASHO published its blue covered publication A Policy on Geometric Design of Rural Highways 11

(10). This document reworked the publications prepared between 1938 and 1944. With increasing 12

urbanization after World War II, AASHO published its 1957 red covered book titled A Policy on Arterial 13

Highways in Urban Areas (11). This “red” book served as the urban supplement to the 1954 “blue” book 14

addressing rural highways. The new edition of the “blue” book was published in 1965 and a revised “red” 15

book edition was published in 1957. These changes reflected research findings and state design and 16

implementation experiences; however, the documents remained focused on providing nominal values. 17

AASHO changed its name in 1973 to the American Association of State Highway and Transportation 18

Officials (AASHTO). In 1984, AASHTO revised the “red” and “blue” books and combined them into one 19

green covered publication titled A Policy on Geometric Design of Highways and Streets. The “green” book 20

has since been revised over the years (1990, 1994, 2001, and 2011). 21

Over the years, revisions accounted for changes in design practice and research findings from various 22

sources. However, with the changes and revisions, the “green” book has remained focused on nominal 23

dimensions based on design controls. Building upon the 1997 FHWA concepts of Flexibility in Highway 24

Design, AASHTO published A Guide for Achieving Flexibility in Highway Design in 2004 (12). This 25

document institutionalized the concept of Context Sensitive Solutions into transportation project 26

development. The intent was to support designer flexibility in considering a project’s particular situation or 27

context and applying the “green” book values accordingly. The document helped users understand how to 28

apply the range of applications in the “green” book to various project conditions encountered; but remained 29

focused on applying the “green” book nominal dimensions. 30

Within three years of publishing the 1984 “green” book, AASHTO members held a national conference on 31

future improvements to and supplemental guidance for its Policy on Geometric Design of Highways and 32

Streets. Held in Austin, Texas, in November 9-11, 1987, the “Beyond the Green Book” conference set the 33

stage for future consideration of improved approaches to highway and street design. In the summer of 34

2002, the AASHTO Technical Committee on Geometric Design and Transportation Research Board (TRB) 35

Geometric Design and Operational Effects of Geometrics Committees met jointly in Santa Fe, New 36

Mexico. The group participated in a joint one-day brainstorming session on research issues and priority 37

research topics organized under the chapter headings of AASHTO’s A Policy on Geometric Design of 38

Highways and Streets (Green Book). A list of topics was generated including performance-based analysis 39

and an alternative highway design process (13). 40

TRB and AASHTO conducted a “Strategic Geometric Design Research Needs Workshop” in 41

Williamsburg, Virginia, in July, 2004. This workshop resulted in a list of research problem statements 42

organized in a prioritized and chronological order for use as a long-range geometric design research 43

program by agencies such as AASHTO, FHWA, and other research sponsoring agencies (13). At the time, 44

the term or practice of “performance-based geometric design analysis” had not been the subject of previous 45

research. However, the group noted an increasing demand for results (i.e., performance) rather than 46


process. Performance characterized in terms of traffic operational measures, safety measures, and 1

maintenance measures were noted as some potential performance criteria. (13). Performance-based analysis 2

was deemed a research priority. 3

AASHTO funded and the NCHRP advertised a request for proposals to conduct Research Project: 15-34 4

Performance-Based Analysis of Geometric Design of Highways and Streets in September, 2005. The 5

research work was awarded and began in 2006. The project was completed under Research Project 15-34A 6

with the findings published in 2014 as NCHRP Report 785: Performance-Based Analysis of Geometric 7

Design of Highways and Streets (3). Completion of the research established a new way to consider and 8

apply information in the AASHTO “Green” book while considering performance categories of: 1) 9

Accessibility; 2) Mobility; 3) Quality of Service; 4) Reliability; and 5) Safety. Performance-based 10

analyses support a broad range of initiatives including context sensitive design/solutions, practical design, 11

flexibility in design, complete streets, and multi-modal design. Designers have new methods and principles 12

from which to customize their design recommendations in considering a range of solutions appropriate to 13

any contextual design environment 14

Framework 15

NCHRP Report 785 documents a fundamental model for performance-based analysis for geometric design 16

of highways and streets (3). The framework provides an approach for understanding the desired outcomes 17

of a project and selecting performance categories and performance measures that align with those 18

outcomes. In addition, the framework outlines how to evaluate the impacts of alternative geometric design 19

decisions on those performance measures to identify solutions that achieve the overall desired project 20

outcomes. This fundamental model is shown in Exhibit 1. 21

Exhibit 1. Fundamental Model for Performance-Based Analysis for Geometric Design of Highways 22

and Streets. 23

24 Source: NCHRP Report 785 (3) 25

Exhibit 1 illustrates the following basic steps in performance-based analysis to inform geometric design: 26


1. Identify intended project outcomes (desired project performance). This may include any number of 1

project context driven categories helping to identify a project need or purpose. These project outcomes (or 2

project performance) help establish the measures by which project and geometric design performance 3

might be measured. 4

2. Make geometric design decisions. This could include establishing design criteria and developing 5

preliminary designs. Geometric design decisions and their emphasis can change through various stages of 6

the project development process. 7

3. Evaluate the performance of the geometric design. This is the point at which the performance 8

outcomes of the geometric design choices are evaluated. It involves assessing geometric design decisions 9

and performance via a performance-based analysis application framework. 10

4. Iterate design and outcomes to optimize. Depending upon the results of the assessment of geometric 11

design performance in relation to intended project outcomes, there can be an iterative process to refine 12

geometric design decisions to bring resulting performance in line with intended project outcomes. If an 13

acceptable solution is not attainable, it may be necessary to re-evaluate intended outcomes. 14

5. Evaluate benefit/costs. In this step the benefits and associated with design choices are assessed to 15

establish the value of the geometric solution compared to the intended project outcomes. If there are two 16

concept solutions that may meet project objectives and all other considerations are equal, the one providing 17

the greater value would likely be advanced. 18

6. Select or advance project(s) or alternatives. As project alternatives are deemed viable within the 19

project context, they may be advanced for more detailed evaluations and/or environmental reviews. 20

Based on the fundamental model above, NCHRP Report 785 documents a process framework for 21

conducting performance-based analyses of highway and street geometric design (3). The framework 22

provides an approach for understanding the desired outcomes of a project and selecting performance 23

categories and performance measures that align with those outcomes. In addition, the framework outlines 24

how to evaluate the impacts of alternative geometric design decisions on those performance measures to 25

identify solutions that achieve the overall desired project outcomes. Exhibit 2 illustrates the framework. 26

Exhibit 2. Performance-Based Analysis Application Framework. 27



The framework can be used throughout the stages of the project development process and within or outside 1

of an environmental review process. The project development stage can help guide the specific 2

considerations for each step in the framework. As shown in Exhibit 2, the framework is organized into 3

three broad phases including: 1) Project Initiation; 2) Concept Development; and 3) Evaluation and 4

Selection. 5

These contain activities to meet the needs of each phase and build incrementally through the steps needed 6

to initiate a project, develop concepts, evaluate options, and ultimately select or advance a project or design 7

recommendations. 8

The Project Initiation phase sets a foundation for understanding the project context and overarching 9

intended outcomes. Understanding the project context may be accomplished through examining existing 10

site constraints, reviewing current performance related to operations, safety, access, reliability and quality 11

of service, and identifying the surrounding land uses and future planned improvements. Outlining the 12

intended project outcomes can be achieved through understanding the motivations for a project, identifying 13

the target audience and desired performance characteristics. The goal of the Project Initiation phase is to 14

identify a clear understanding of the project purpose and the characteristics defining the current and desired 15

future of the project site. This information will lead help develop to a clear a set of performance measures 16

to be used to evaluate a design’s impact on the desired project purpose. 17

Concept Development focuses on developing potential solutions to address the intended project outcome 18

and may include evaluating discrete design decisions of a geometric element or configuration. At the 19

beginning stages of the project development process, Concept Development will include identifying 20

overarching alternatives, such as alternative intersection forms, roadway alignments, roadway cross-21

sections, or interchange forms. During later stages of the project development process, Concept 22

Development becomes more detailed, focusing on specific solutions, such as adjusting a horizontal curve. 23

Regardless of the project development stage, within the Concept Development phase there are geometric 24

features that will influence the performance of the ultimate roadway facility and a set of potential solutions 25

whose resulting performance can be evaluated to help determine which solution is preferred. Geometric 26

influences are the geometric characteristics or decisions that can influence a project’s performance as it 27

relates to the categories of Accessibility; Mobility; Quality of Service; Reliability; and Safety. It also 28

includes geometric characteristics or decisions influenced by the desired performance of a project. The 29

information is essential in developing potential solutions that make progress towards the intended project 30

outcomes. 31

The Evaluation and Selection phase uses the potential solutions outlined in the Concept Development 32

phase to directly integrate performance-based analysis to further refine those solutions. The two primary 33

steps within this phase include estimating performance and financial feasibility of a potential project. The 34

performance of a project is evaluated relative to the previously identified performance categories and 35

associated measures. Next, the financial feasibility of each alternative is considered to decide if there is an 36

alternative that sufficiently meets the project’s intended outcome and is financially feasible. This phase will 37

result in one of the following two outcomes: 1) Return to the Concept Development phase for further 38

solution development or refinement; or 2) A selected project. 39

Based on the results from the estimated performance and financial feasibility step described in the 40

Evaluation and Selection phase, a preferred alternative is selected or the project team may decide to 41

further refine alternatives and re-evaluate their performance. While there may be other external factors or 42

qualitative performance measures driving the decision to select a preferred alternative or further refine and 43

re-evaluate alternatives, there are some key questions that may help identify how to best advance a project 44

to the next stage in the project development process. These questions may include: 45

Are the performance evaluation results making progress towards the intended project 46

outcomes? 47

Do the alternatives serve the target audience and achieve the desired objectives? 48


Can reasonable adjustments be made to the geometric design elements most significantly 1

influencing project performance? 2

Do the performance measures help differentiate between the alternatives? 3

As noted previously, the framework can be used within or outside of an environmental review process. The 4

performance-based analysis framework can benefit practitioners in developing a draft EIS, selecting a 5

preferred alternative in the final EIS, and identifying the means to avoid and minimize environmental 6

impacts. The Project Initiation phase can be used to develop a clear and focused project purpose and need 7

statement. The Concept Development and Evaluation and Selection phases can be used to develop 8

reasonable alternatives that perform to a level to fulfill the project purpose and need while avoiding or 9

minimizing environmental impacts. The Evaluation and Selection phase can also be used to help identify 10

the preferred alternative. The overall performance-based analysis framework can also be used to facilitate 11

the comprehensive documentation needed within the EIS process. 12

Application 13

The performance-based analysis to inform geometric design decisions can be integrated into a wide range 14

of projects and tailored to fit the context of what the project team is striving to achieve. Chapter 6 of 15

NCHRP Report 785 presents a series of project examples illustrating how transportation professionals can 16

use the performance-based analysis framework across urban, suburban, and rural contexts for intersection 17

design considerations, streets, highways, and freeway and interchange system planning (3). Exhibit 3 18

summarizes the example projects contained in Chapter 6 of NCHRP Report 785 (3). 19

Exhibit 3. Summary of Project Examples in NCHRP Report 785. 20

Project Example

Site - Area and Facility Type

Project Development

Stage Performance Categories Project Type

1 US 21/Sanderson Road - Rural Collector (Two-Lane Highway)

Alternatives Identification and Evaluation

Safety Intersection – Consider alternative intersection control to improve safety.

2 Richter Pass Road - Rural Collector

Preliminary Design

Safety Mobility

Segment – Consider alternative horizontal curve radii to improve safety while minimizing costs and maintaining appropriate speed.

3 Cascade Ave - Suburban/Urban Arterial

Preliminary Design

Safety Mobility Reliability Accessibility Quality of Service

Corridor – Retrofitting an existing auto-oriented urban arterial to incorporate complete street attributes. Focus on alternative street cross-sections.

4 SR 4 - Rural Collector Preliminary Design

Safety Reliability Quality of Service

Segment – Consider alternative shoulder widths and sideslopes to minimize impact to an environmentally sensitive area.

5 27th Avenue - Urban Minor Arterial


Quality of Service Safety Accessibility

Segment – Alignment and cross-section considerations for new urban minor arterial being constructed to entice employers to a newly zoned industrial area.

6 US 6/Stonebrook Road - Rural Interchange


Safety Mobility

Interchange Converting an at-grade rural

intersection to a grade-separated interchange.

Focus on selecting the appropriate interchange form and location (e.g., spacing considerations).

Source: NCHRP Report 785 (3) 21


The project examples were developed from actual projects that have integrated performance-based analysis 1

into design decisions and/or could have benefited from incorporating performance-based analysis into 2

design decisions. Some of the project examples were created to illustrate performance-based analysis 3

process and communicate key learning objectives. In each project example, the names are changed and do 4

not reflect the actual names of the facilities or agencies. 5

The following sub-sections provide a synopsis of three of the six project examples. The three project 6

examples that are touched on below address rural and urban contexts; application to intersections and 7

roadway segments; consider changes in roadway cross-section, intersection traffic control and roadway 8

alignment; address multiple performance categories; and include multiple modes. 9

Project Example 1: US 21/Sanderson Road Intersection 10

The US 21/Sanderson Road intersection example illustrates how the performance-based analysis 11

framework can be integrated into evaluations and decisions considered when evaluating alternative 12

intersection traffic control. This particular intersection is located on a rural two-lane roadway with a posted 13

of 55 mph. 14

The project example discusses the project context and defines the intended project outcomes. The outcomes 15

are focused on improving safety and enhancing the intersection to be a gateway to the adjacent community. 16

Safety is the primary performance category of interest within this project. Based on these intended 17

outcomes, a set of performance targets (e.g., reducing severe crashes) and related geometric design 18

decisions (e.g., intersection control) are identified. These help inform the project team in identifying and 19

developing potential solutions for the intersection. The alternatives considered for the intersection were: 1) 20

Single-lane roundabout (Exhibit 4); and 2) Traffic signal (Exhibit 4); and 3) Low-cost pavement marking 21

and signing enhancements to the existing two-way stop controlled intersection. Using performance analysis 22

resources such as the Highway Safety Manual (HSM) (14), the project example illustrates the expected 23

crash performance at the intersection with the different traffic control designs. It includes planning level 24

cost estimates to be able to gauge the cost effectiveness of the alternatives by calculating the cost per crash 25

mitigated over the design life of each alternative. 26

Exhibit 4. Roundabout Concept and Traffic Signal Concept. 27


From the performance-based analysis process and results, the project team, including the agencies 29

involved, was able to objectively and quantitatively consider the relative safety performance of the different 30

alternatives relative to their costs. Based on this comparison, they selected the roundabout alternative in 31

combination with way-finding and gateway treatments. The application of performance-based analysis in 32

this project example is readily transferable to intersection design and traffic control feasibility studies in 33

other rural contexts, urban areas, and suburban communities. It can also be expanded to include other 34


performance measures discussed in NCHRP Report 785 such as mobility, quality of service for different 1

modes of travel, and accessibility (3). 2

Project Example #2: Richter Pass Road 3

The Richter Pass Road example illustrates incorporating performance-based analysis into a corridor study 4

for a rural two-lane roadway where surrounding land uses have evolved from rural to increasingly 5

suburban. The roadway traverses a hillside that has experienced increasing amounts of residential 6

development adjacent to the roadway and accessing the roadway. The roadway frequently has steep side 7

slopes with drop offs on one side and retaining walls or cuts through rock on the other side of the roadway. 8

The corridor has experienced a steady increase in traffic volume as well as crashes. 9

The project example discusses the project context and highlights the low-cost treatments previously 10

implemented along Richter Pass Road. A defining feature of the roadway is that the original design speed is 11

55 mph, the posted speed is 45 mph, and there are advisory speed signs for horizontal curves along the 12

roadway for as low as 15 mph. The topography the roadway traverses and the resulting alignment does not 13

create a consistent or predictable roadway for motorists. The intended project outcomes are focused on 14

reducing crash frequency and severity while maintaining a reasonable level of mobility the commuter 15

traffic using the roadway. 16

Exhibit 5. Previously Implemented Low Cost Treatments. 17

18


A unique characteristic of this example is the use of FHWA’s Speed Concepts: An Informational Guide to 20

identify a range of alternative alignments that would create a more consistent driving experience for 21

motorists (15). The alternatives range from a Minimal Improvements to Ultimate Improvements concepts 22

with two additional variations that present a practical design approach and a more traditional interim 23

approach. In this example, the HSM and FHWA’s Speed Concepts: An Informational Guide are used to 24

evaluate the potential performance of each alternative (14, 15). Planning cost estimates for each of the 25

alternatives were developed and are compared to the potential performance of the alternative to gauge cost 26

effectiveness. 27

Within this example, the Practical Improvements alternative, developed using principles of practical design, 28

was selected as the preferred alternative. This alternative provided the most cost effective enhancements for 29

safety and mobility while fitting the project context and available funding. 30

Project Example #3: Cascade Avenue 31

The Cascade Avenue example integrates performance-based analysis into an urban, multimodal context 32

within a project that is focused on reallocating existing roadway right-of-way to better serve a wider range 33

of road users. This example represents an increasingly common project type that cities, counties and states 34

across the U.S. are encountering. Projects like Cascade Avenue are sometimes referred to as complete 35

streets projects, road diet projects, and/or context sensitive solutions. An increasing number of guidebooks 36


are being produced and published by organizations such as the National Association of City Transportation 1

Officials (NACTO) whose publications such as Urban Street Design Guide and Urban Bikeway Design 2

Guide provide a range of innovative treatments reallocating roadway cross-sections to improve quality of 3

service for pedestrians, bicyclists and transit (16, 17). 4

Cascade Avenue is an urban arterial with four-lane undivided roadway cross-section with on-street parallel 5

parking on both sides of the roadway. It connects a vibrant downtown core with an active university 6

campus. The intended outcome of the project is to make Cascade Avenue a more comfortable, safe, and 7

attractive urban street for transit riders, pedestrians and bicyclists. The local business community would 8

also like to see improvements that increase economic vitality along the corridor with a particular focus on 9

local small business success. Exhibit 6 illustrates one of the alternative cross-sections evaluated. 10

Exhibit 6. Alternative 3 – Bicycle and Pedestrian Oriented. 11


This project examples uses performance measures from the full range of performance categories addressing 14

safety, mobility, quality of service, accessibility, and reliability across modes. The potential solutions focus 15

on alternative cross-sections with some cross-sections oriented more towards one or two modes (e.g., 16

Alternative 2 is the transit-oriented cross-section). The performance-based analysis evaluates each 17

alternative relative to the performance measures that assess the safety, mobility, reliability, quality of 18

service, and accessibility across the different modes. The performance-based analysis results illustrate the 19

wide range of tradeoffs between modes across the alternative. Ultimately, the project team and agency 20

selected Alternative 2, the transit-oriented alternative, as the preferred based on the balance of performance 21

and modes. 22

In addition to illustrating how performance-based analysis could be incorporated into these complete street, 23

road diet, and/or context sensitive solutions projects, the tradeoffs and consideration specific to Cascade 24

Avenue also illustrate the importance of considering the desired function of an urban road in the context of 25

the broader roadway network. From the performance-based analysis results, it is clear that not every street 26

is able to serve every user equally well. As a result, it is useful for project teams and agencies to understand 27

the intended or necessary function of the roadway as it relates to the broader street network. 28

Summary of Applications 29

The performance-based analysis framework provides flexibility for practitioners to be able to integrate 30

performance-based analysis into their design and project decisions under a variety of project contexts and 31

throughout the project development process. The above project examples represent a range of project types; 32

the additional three project examples in NCHRP Report 785 address application in the context of potential 33

environmental impacts, balancing modes through a redeveloping light industrial area, and application to an 34

interchange project (3). 35

36


Conclusion 1

Highway and street geometric design has evolved significantly over the last century. Early roadway design 2

considerations were focused primary on quality of travel and adapting to weather related issues. As the 3

automobile became a popular transportation vehicle, low traffic volumes and relatively low speeds did not 4

reveal a need for significant changes and quality of travel and year-round use remained a priority. From the 5

1920’s through 1940’s, traffic volume had grown and motorized vehicles became a dominant transportation 6

mode. Vehicle designs advanced, speeds increased, and highway and street design evolved steadily to react 7

to and adapt to the changing conditions. During much of this time, AASHO objectives and associated 8

policies emphasized design consistency on similar roadway types across the states. 9

The various policy documents evolved and were combined as documents not dissimilar to policies today. 10

Of course there were advances as the art of geometric design advanced, as designers learned lessons from 11

the past, and applied research led to quantifying design criteria. However, the highway and street design 12

process has essentially remained tied to process and nominal design values. The evolution in roadway 13

design has been positive and resulted in high quality roadways serving a diverse range of users. And 14

despite the amount of design resources available, designers still apply engineering judgment in the best 15

design circumstances. 16

Increasingly, roadway agencies have limited resources to invest and often are developing projects within a 17

physically constrained environment (e.g., limited right-of-way in an urban area, minimizing impacts in 18

environmentally sensitive areas). It is not always fiscally possible or reasonable to categorically construct 19

roadways to meet design standards. Through initiatives such as context sensitive solutions and practical 20

design, as a profession, we have learned that in many circumstances we must construct roadways using 21

flexible design approaches to adapt to the unique need of each contextual design environment. 22

A performance-based analysis approach advances street and highway design by first understanding the 23

desired outcomes of a project, selecting performance categories and performance measures that align with 24

those outcomes, evaluating the impact of alternative geometric design decisions on those performance 25

measures, and arriving at solutions that achieve the overall desired project outcomes. The approach is 26

adaptable to each stage of the project development process, and focuses on the performance effects of 27

geometric design decisions. When considering how performance outcomes relate to the investment needed 28

to achieve various outcomes, one can consider the potential benefits compared to the associated investment. 29

The performance-based approach can support project documentation needs and can, overall, inform and 30

guide project decision making while supporting risk management objectives. 31

NCHRP Report 785: Performance-Based Analysis of Geometric Design of Highways and Streets 32

documented a process framework for conducting performance-based analyses of highway geometric design 33

(3). The performance-based approach supports project documentation needs and can, overall, inform and 34

guide project decision making while supporting risk management objectives. This methodology is based 35

on first, understanding intended project outcomes, and then subsequently considering and selecting 36

geometric design elements or features that best meet a project’s unique context. A performance-based 37

approach gives primary consideration to the respective stage of the project development process, and 38

provides complementary focus on the performance effects of resulting geometric design decisions. 39

References 40

1. The Evolution of Performance-Based Codes and Fire Safety Design Methods , Brian J. Meacham, 41

Society of Fire Protection Engineers, Boston, MA, 1996 42

2. Next Generation Performance-Based Seismic Design Guidelines, FEMA-445, August 2006 43

3. Report 785: Performance-Based Analysis of Geometric Design of Highways and Streets, 44

National Coooperative Highway Research Program, Washington, DC, 2104 45


4. America’s Highways- 1776-1976, A History of the Federal-Aid Highway Program, U.S. 1

Department of Transportation, Federal Highway Administration, U. S. Government Printing 2

Office, Washington, D. C., 1976. 3

5. The Evolution of Roadway Design and its Relationship to Design Immunity, Blaschke and 4

Rowan, 1991 5

6. A Policy on Highway Classification, American Association of State Highway Officials, 6

Washington, D.C., 1938. 7

7. A Policy on Sight Distance for Highways, American Association of State Highway Officials, 8

Washington, D.C., 1940. 9

8. A Policy on Criteria for Marking and Signing No-Passing Zones on Two and Three Lane Roads, 10

American Association of State Highway Officials, Washington, D.C., 1940. 11

9. A Policy on Design Standards, American Association of State Highway Officials, Washington, D. 12

C., 1945. 13

10. A Policy on Geometric Design of Rural Highways, American Association of State Highway 14

Officials, Washington, D. C., 1954. 15

11. A Policy on Arterial Highways in Urban Areas, American Association of State Highway Officials, 16

Washington, D. C., 1957. 17

12. A Guide for Achieving Flexibility in Highway Design, American Association of State Highway 18

and Transportation Officials, Washington, D. C., 2004. 19

13. Geometric Design Strategic Research, Transportation Research Circular E-C110, Transportation 20

Research Board, Washington, DC, 2007. 21

14. Highway Safety Manual, American Association of State Highway and Transportation Officials, 22

Washington, D. C., 2010. 23

15. Speed Concepts: Informational Guide, Federal Highway Administration, Washington, D.C., 2009. 24

16. Urban Streets Design Guide, National Association of City Transportation Officials, New York, 25

NY, 2013. 26

17. Urban Bikeway Design Guide, National Association of City Transportation Officials, New York, 27

NY, 2012. 28

Documents

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