Use of Narrow Lanes and Narrow Shoulders on Freeways: A Primer on Experiences, Current Practice, and Implementation Considerations

Chapter 2. Performance Based Practical Design and the Role of Operations

Performance Based Practical Design

Performance-Based Practical Design (PBPD) modifies the traditional "top down, standards first" approach to a "design up" approach where designers and decision makers exercise engineering judgment to build up the roadway and operational improvements from existing conditions to meet both project and system objectives. PBPD uses appropriate analysis tools — such as those discussed in Chapter 4 — to evaluate the performance impacts of planning and design decisions in relation to the cost of providing various geometric elements and operational features.

PBPD should not be viewed as a stand-alone set of activities. Rather, it is an integral part of a broader process known as "Performance-Based Planning and Programming." The Federal Highway Administration (FHWA) publication "Performance Based Planning and Programming Guidebook" (Reference 25) describes the application of performance management principles within the planning and programming processes of transportation agencies and regional entities (e.g., Metropolitan Planning Organization (MPOs)) to achieve desired performance outcomes for the multimodal transportation system. Figure 2 shows the Performance-Based Planning and Programming (PBPP) process, indicating where PBPD concepts and activities may be applied. As shown in Figure 2, PBPDrelated activities can be applied to the preliminary engineering and design activities, with any cost savings going to support additional projects as part of the regional programming process.

PBPD concepts can also be used during planning activities to help identify strategies and analyze alternatives.

Figure 3 identifies and summarizes the various PBPD concepts and potential activities, starting with "baseline conditions" including design policies and guidelines, current and projected issues and needs, and stakeholder concerns; and then moving into analysis such as developing alternatives, analyzing these alternatives in terms of improved performance and costs, coupled with trade-offs and engineering judgment. The results of these PBPD-related activities and concepts (i.e., "Moving Forward") is the selection of the optimal concepts and strategies for design, the identification of any design exceptions, and the documentation of the decisions. The optimal design concepts, along with any associated cost savings, are fed back into the PBPP framework.

As collectively shown in Figures 2 and 3, with PBPD designers apply a "design up" approach by using existing conditions as the baseline and engineer solutions that meet the project purpose based on explicitly defined transportation performance needs as derived from system and regional goals and objectives. This approach differs from a more conventional approach of setting project design criteria based solely on values listed in design specifications or standards for a set of given conditions. Designers then evaluate the solutions against the tradeoffs based on an objective analysis of performance data. Some of the tradeoffs considered include the estimated costs for each potential solution, coupled with due consideration of agency polices, legal requirements, stakeholder sensitivities, and any other potential constraints.

Note: Performance-Based Practical Design shown in orange.
Figure 2. Diagram. Framework for Performance-Based Planning and Programming.
(Source: Adapted from Federal Highway Administration document number HEP-13-041, Reference 25)

Figure 3. Diagram. Concepts and Activities Associated with Performance-Based Practical Design.
(Figure is based on several Federal Highway Administration documents and presentations on the subject of Performance-Based Practical Design)

A basic tenet of PBPD involves making project decisions that directly serve performance needs while considering whether the same investment of money would yield a greater return on investment if applied to other system needs and/or priorities. It is important to document the design decisions and present them to decision makers showing the benefits relative to the no-build option. These PBPD design and decision-making analyses can easily be transferred to design exception forms for review, approval and record-keeping.

By implementing a PBPD approach, agencies may reduce or eliminate project elements that are determined to be non-essential, resulting in lower cost and improved value by taking advantage of existing design flexibility. Agencies may also use the associated cost saving to deliver a greater number of projects that yield a greater performance return on investment than otherwise possible under existing project development and design approaches.

Relationship Between PBPD and Context Sensitive Solutions

Context-sensitive solutions (CSS) seek a transportation solution that addresses the needs of all road users and the functions of the facility within the context of its setting, considering land use, users, the environment, and other factors. CSS is a collaborative, interdisciplinary approach that includes the viewpoints of all stakeholders in the development of a shared vision of project goals, and uses a defined decision-making process. CSS and PBPD rely on flexibility to achieve results that meet the project purpose and need. PBPD compliments CSS by providing performance information that supports decision-making.

Design Criteria and Design Exceptions

As previously noted, PBPD moves away from the more conventional "top down, standards first" approach to more of a performance and valuebased "design up" approach. Designers that focus on the relationships between design dimensions and performance may become less obligated to meet one or more of the design guidelines, such as those found in the AASHTO Green Book ("A Policy on Geometric Design of Highways and Streets"). Design criteria and standards offer many benefits, including promoting consistency, establishing a design "norm", and promoting efficiency in design development. However, "standard" does not necessarily mean "best", nor are standards intended to be a substitute for engineering judgment and context-specific considerations. PBPD provides planners and designers with the flexibility to make the optimum design decisions.

A design exception is a documented decision to design a highway element or a segment of highway to design criteria that do not meet minimum values or ranges established for that highway or project. Federal regulations (Reference 13) state that "Approval …may be given on a project basis to designs which do not conform to the minimum criteria as set forth in the standards, policies, and standard specifications." A design exception is NOT an indication of failure or a "flawed" design; rather it is a necessary and legitimate process to allow professional and engineering judgment in the design process, providing a useful "tool" for employing practicality and flexibility in design decisions in a design-up approach such as PBPD.

As noted in the FHWA document “Mitigation Strategies for Design Exceptions” (Reference 14) there are a broad range of reasons why design exceptions may be considered and found to be necessary. Some of these include the following:

• Impacts to the natural environment
• Social or right-of-way impacts
• Preservation of historic or cultural resources
• Sensitivity to context and community values
• Construction or right-of-way costs

Widening the roadway footprint, including the possibility of additional right-of-way, will certainly impact the last bullet, and may impact one or more of the other bullets. Adding a lane by narrowing the existing lanes within the existing roadway footprint can help reduce or even eliminate the concerns noted above in the bulleted list that so often apply to projects that end up widening the roadway.

A final notice published in the Federal Register on May 5, 2016 completed FHWA's effort to update the policy regarding controlling criteria for design, applicable to projects on the National Highway System. FHWA reduced the number of controlling criteria from 13 to 10 for Interstate highways, other freeways, and roadways with design speed ≥ 50 mph, and now applies only 2 of those criteria to low speed roadways (non-freeways with design speed < 50 mph). FHWA also clarified when design exceptions are needed and the documentation that is expected to support such requests.

FHWA has adopted new policies to modify highway design standards that encourage greater flexibility in order to achieve a design that best suits the desires of the community, while satisfying the purpose for the project and needs of its users. As an example, FHWA published revisions to current federal policy that will help reduce cost and speed up the design of local roads and streets. In 1985, thirteen design criteria were prioritized because of their perceived impact on operations and safety. Under the new policy, ten criteria will be prioritized for high speed roadways, and only two criteria will be emphasized for lowerspeed roads such as rural roads that become main streets through smaller towns and cities. This will provide state and local engineers to develop flexible design solutions that meet local travel needs and goals.

Chapter 8 of the Green Book recommends shoulder widths for freeways shown in Table 4. Additionally, the AASHTO policy on design standards for the Interstate highway system requires a 10 ft. paved right (outside) shoulder. Shoulder widths less than the values shown in Table 4 will also require a design exception under the existing and proposed FHWA policy on Controlling Criteria.

Moving the inside travel lane closer to the roadway edge — including part time use of the shoulder as a travel lane — may also impact the horizontal alignment (to be renamed as "horizontal curve radius" under the proposed FHWA policy on Controlling Criteria) and sight distance as shown in Figure 4, and may therefore also require a design exception.

Table 4. Recommended Shoulder Widths for Freeways.

Side of Roadway	DDHV for truck traffic (veh/hr)	Total numbers of freeway lanes	Recommended shoulder width (ft)
Right Shoulder	≤ 250	All	10
Right Shoulder	> 250	All	12
Left Shoulder	≤ 250	Less than 6	4
Left Shoulder	≤ 250	6 or more	10
Left Shoulder	> 250	All	12

(Source: NCHRP Report 783: Evaluation of the 13 Controlling Criteria for Geometric Design; adapted from Chapter 8 of the AASHTO Green Book)

Figure 4. Diagram. Potential Impact on Sight Distance From Moving the Left-Most Travel Lane To the Inside.

Transportation Systems Management and Operations

Transportation Systems Management and Operations (TSMO) — also often referred to simply as "operations" — is defined as:

Intelligent Transportation System (ITS) technologies — be they devices for monitoring traffic flow on the roadways, hardware and software at Transportation Management Centers (TMCs), and/or "Connected Vehicle" applications — are crucial to the success of these operations strategies. ITS represents the “enabling technology for operations.”

TSMO strategies — coupled with the supporting ITS technology — are a most important aspect of delivering transportation services to customers. Experience has shown that aggressive applications of these operations strategies can, in effect, "take back" much of the capacity lost due to congestion and disruptions. Operations strategies also enhance safety, promote reduced emissions, and increase system reliability.

Perhaps most importantly, actively managing the transportation network can improve travelers' experiences, providing them with real-time information and choices throughout the trip chain — from origin to destination — leading to network performance optimization and increased efficiency. TSMO strategies are relatively low cost (compared with adding capacity), much quicker to implement (two to three years), and offer substantial benefits (with very positive benefit-cost ratios).

FHWA recommends an "objectives-driven, performance-based approach" for including "operational and management strategies to improve the performance of existing transportation facilities" in the planning process. This objectives-driven, performance-based approach to planning for operations within a metropolitan area — conducted in collaboration among planners, transportation providers, operators, and other stakeholders — is shown in Figure 5.

The activities shown in Figure 5 parallel the PBPP and PBPD concepts identified in previous Figures 2 and 3, including the development of potential strategies based on goals, objectives, and needs; and then evaluating and subsequently selecting strategies in terms of performance and cost. Moreover, lowcost, rapidly deployable, and flexible treatments — as provided by many TSMO strategies — all fall under the collective umbrella of PBPP and PBPD. Table 5 provides a list of TSMO strategies that may be used in conjunction with narrow lanes and/or shoulders as part of the PBPD process.

Figure 5. Flowchart. An Objectives-Driven, Performance-Based Approach.
(Adapted from Federal Highway Administration, Reference 25)

Table 5: Transportation System Management and Operations Strategies Typically Used On Freeways and the Potential Relationships to Performance-Based Practical Design.

TSMO Strategy	Description	Potential Use and Value in Narrow Lanes/Shoulders
Incident Management	The systematic, planned, and coordinated use of human, institutional, electrical, mechanical, and technical resources to reduce the duration and impact of incidents, and improve the safety of motorists, crash victims, and incident responders.	Used to address safety and reliability concerns of narrow lanes or the loss of the shoulder as a vehicle refuge.
Ramp Management	The application of control devices, such as traffic signals, signing, and gates to regulate the number of vehicles entering or leaving the freeway, or to smooth out the rate at which vehicles enter and exit the freeway.	Metering the traffic that enters the freeway from on-ramps can help prevent flow breakdown on the mainline, and improve safety in merge and weaving areas that may be impacted by the use of narrow lanes and/or shoulders.
Managed Lanes (HOV,HOT)	Highway facilities or a set of lanes where operational strategies are proactively implemented and actively managed to optimize traffic flow and vehicular and person throughput. These strategies typically involve pricing, vehicle eligibility, and access control.	Used to improve travel time and reliability for vehicles carrying the most passengers or those willing to pay an additional fee for using the lane. The use of narrow lanes and shoulders may provide the opportunity to add or expand such lanes.
Traveler Information (511, apps on Smartphones, DMS)	A combination of strategies for enabling better traveler decision making throughout the trip chain — before, during, and near the end of a trip.	Allows drivers to adjust their route, time of travel, or mode, thus lessening demand on key facilities at peak times. DMS can also alert motorists that queues, significant slowdowns, or blocked lanes are ahead — as may result from narrow lanes or shoulders — thus reducing rear-end crashes and improving safety.
Dynamic Speed Limits	Adjusts speed limit (or advisory) displays based on real-time traffic, roadway, and/or weather conditions. They can be applied to an entire roadway segment or individual lanes. This "smoothing" process helps minimize the differences between the lowest and highest vehicle speeds.	Used to reduce speeds in advance of congestion, or perhaps in advance of segments with narrow lanes, limited shoulder widths, or reduced sight distance (e.g., requiring a reduced design speed as part of the design exception process). Is often used in conjunction with part time shoulder use, dynamic lane assignment. (Refer to Figure 6)
Dynamic Lane Assignment	Dynamically closing or opening individual traffic lanes as warranted and providing advance warning of the closure(s), typically through lane control signs, to safely merge traffic into adjoining lanes.	Used to open and close a part time lane (e.g., part time shoulder use), or to close lane(s) upstream of a crash or disabled vehicle (e.g., with no shoulder for refuge). One or more lanes may also be closed to allow emergency vehicles to reach the crash scene quicker, particularly if there are narrow shoulders. This strategy is often used in conjunction with dynamic speed limits.
Dynamic Junction Control	Dynamically allocating lane access on mainline and ramp lanes in interchange areas. This may consist of assigning lanes dynamically either for through movements, shared through-exit movements, or exitonly.	Used to better allocate available capacity at interchange areas and reduce the amount of weaving and merging. Is typically used with some sort of dynamic lane assignment. May be deployed to identify if the ramp shoulder is open to traffic and which mainline lanes can access the ramp; or may be deployed to promote safe merging operations during use of the mainline shoulder.

Incorporating the consideration of TSMO strategies into the PBPD concepts and activities, designers and decision makers can expand the variety of options available to them, including perhaps the ability to postpone or reduce the need for conventional capacity improvements. Additionally, TSMO strategies may also help mitigate some of the safety and reliability impacts of PBPD solutions that result in less than full standard geometric design decisions, thereby providing solutions and support for any design exceptions. For example, dynamic speed limits and dynamic lane assignment strategies may be used in this context as shown in Figure 6.

Figure 6. Diagram. Example of Dynamic Speed Limits and Dynamic Lane Assessment in Support of Narrow Lanes and Shoulders.

In summary, PBPD and TSMO — along with Context Sensitive Solutions and value engineering — are very complimentary as shown in Figure 7. Their respective approaches have much in common, and they all strive for the same goal — namely, providing a wellperforming transportation system using the most cost-effective improvements.

The FHWA website for PBPD (Reference 12) identifies notable attributes for PBPD as listed below. The phrase "and TSMO" can be added immediately after "PBPD" in this list and still ring very true.

• PBPD (and TSMO) focuses on performance improvements that benefit both project and system needs.
• Agencies make sound decisions based upon performance analysis.
• By scrutinizing each element of a project's scope relative to value, need, and urgency, a PBPD (and TSMO) approach seeks a greater return on infrastructure investments.
• PBPD (and TSMO) strengthens the emphasis on planning-level corridor or system performance needs and objectives when planning, scoping and developing individual projects.
• PBPD (and TSMO) can be implemented within the Federal-aid Highway Program regulatory environment utilizing existing flexibility. PBPD does not eliminate, modify, or compromise existing design standards or regulatory requirements.

Figure 7. Diagram. Overlapping Relationship between Performance-Based Practical Design, Performance-Based Planning and Programming, Transportation System Management and Operations, Context SensitiveSolutions, and Value Engineering.