Work Zone Road User Costs - Concepts and Applications
Chapter 3. Application of WZ RUC during MOT Alternative Analysis
A MOT strategy is a temporary application of traffic control measures and devices to facilitate road users through work zones. The functions of a MOT strategy are to (1) provide reasonably safe and effective movement of traffic through or around the work zones, (2) reasonably protect road users, workers, responders to traffic incidents, and equipment, and (3) facilitate the efficient completion of the
A temporary traffic control strategy can be enhanced into a comprehensive TMP by adding features such as construction staging, phasing, safety improvements, enforcement of traffic regulations, incident management, public involvement and outreach programs, traffic operations at the corridor or network level, non-traditional contractual arrangements, and innovative construction techniques.
MOT alternative analysis is an assessment of competing strategies to determine one that best mitigates the adverse mobility, safety, environmental, business, and community impacts of a construction work zone at reasonable agency and WZ RUC. The analysis considers potential benefits, costs, and constraints associated with each feasible alternative and their effectiveness in managing work zone impacts.
The selection of an MOT alternative for a project depends on factors such as the significance of mobility and safety impacts, project type and complexity, urban/rural location, construction factors, constructability constraints, agency and road user costs, agency policies, and aspects of the surrounding area (e.g., availability of alternate routes, nearby businesses). Therefore, to devise an effective MOT strategy, it is imperative to take these influencing factors into consideration in a systematic manner on a project-by-project basis.
The MOT alternative analysis evolves over the various stages of project development. In the planning stage, the agency conducts a cursory qualitative assessment to evaluate the criticality of the proposed work zone impacts as well as the system needs, constraints, and deficiencies (e.g., agency policies or resource availability). Based on the impact assessment, a decision is made whether there is a need for conducting a detailed MOT alternative analysis. For projects with low to moderate impacts, the agency may find conventional strategies adequate (e.g., permitted lane closure timings), while the projects with significant impacts may require a more detailed impact assessment and MOT alternative analysis.
In the preliminary engineering stage, candidate MOT strategies are identified based on the potential design, construction techniques, phasing, and contracting strategies. Quantitative analysis of work zone impacts is conducted at this point using sketch-planning tools and deterministic tools to analyze the effectiveness of each candidate strategy. For projects with low to moderate impacts, this level of analysis would suffice. For more complex projects with significant impacts, simulation tools can be employed.
The agency sets performance goals (threshold values) for each performance measure based on agency policies and project-specific needs to ensure a minimum acceptable level of work zone performance. The expected benefits, costs, and constraints associated with each candidate alternative are evaluated against the performance thresholds, and against each other, and ranked to determine the preferred alternative. Based on this evaluation, an alternative that best meets the criteria is selected as the preferred alternative using decision analysis tools.
In the design stage, a further work zone impacts assessment is conducted, if required, to finalize the preferred MOT strategy. The design and construction details are refined as the project progresses from preliminary engineering and design stages, and therefore, inputs and assumptions used in the MOT alternative analysis will have to be revised accordingly.
In the construction stage, unforeseen situations such as a change in the original construction schedule, construction technique, or the TMP may warrant reassessing the selected MOT strategy or reanalyzing the work zone impacts. The contractor also may propose value engineering solutions to the selected MOT strategy.
The steps involved in the MOT alternative analysis process are listed below and discussed in greater detail in the following sections:
- Perform preliminary analysis of work zone impacts using available project information.
- Identify the need for MOT alternative analysis based on preliminary analysis of work zone impacts. If there is a need for MOT alternative analysis, go to Step 3.
- Identify candidate strategies for MOT alternative analysis.
- Identify performance measures and thresholds.
- Conduct detailed analysis of work zone impacts when the final design is complete.
- Use Kepner-Tregoe method to select a preferred MOT strategy.
MOT alternative analysis typically begins with a cursory assessment of work zone impacts in the early planning stages of the project. The available information on project scope and duration, roadway/traffic characteristics, and other contributing factors (local communities, businesses, traveling public, etc.) is compiled and evaluated. More detailed discussion can be found in the FHWA’s guidance on the work zone impact assessment. (Sankar, P., K. Jeannotte, J. P. Arch, M. Romero, and J. E. Bryden, Work Zone Impacts Assessment - An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects, Report No. FHWA-HOP-05-068, Office of Operations, Federal Highway Administration, Washington, DC, 2006.)
Though qualitative in nature, this assessment evaluates how the proposed work zone will affect the mobility, safety, and economical impacts of the traveling public and the community at large. It provides a general sense on the magnitude of work zone impacts, which are in turn used to establish the significance of the project type and the need for conducting a detailed MOT alternative analysis.
The assessment helps to identify issues relating to project scheduling, potential construction approaches and contractual arrangements, funding constraints, availability of agency resources and analysis tools, agency policies, concurrent projects and coordination issues, and their potential effects on work zone impacts. The findings of this assessment are used in identifying candidate strategies for the MOT selection process. Early impact assessment helps to limit the number of candidate strategies considered in the MOT alternative analysis and to develop a better end product. (Bourne, J. S. et al, Best Practices In Work Zone Assessment, Data Collection, and Performance Evaluation, NCHRP Project 20-68A Scan 08-04, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, 2010.)
Some of the typical factors that would be considered in the preliminary evaluation include:
- Facility type: freeway, principal arterial, collector, local etc.
- Area type: rural or urban.
- Project type and complexity.
- Expected construction duration.
- Need for early completion.
- Strategic importance of the roadway.
- Traffic volume.
- Level of service – the adequacy of roadway capacity to accommodate traffic demand.
- Peak hour traffic demand.
- Commuter traffic.
- Availability of detour alternatives.
- Ability of detour routes to accommodate diverted traffic volume.
- Likelihood of getting lost in detours.
- Adequacy of lane shoulder width.
- Interference with contractor access to work zone.
- Need to consider business impacts.
- Level of public interest.
- Need to consider local ordinances on noise for night work.
- Safety risks to motorists and construction workers.
- High incidence areas.
The next step in the MOT alternative analysis process is to determine the relative impact based on the project size and complexity, expected duration of construction, traffic volume affected, and the magnitude of mobility, safety, and economical impacts. The purpose of this step is to identify the level of effort and resources required for MOT alternative analysis commensurate with the magnitude of work zone impacts.
Based on this guidance, FHWA specifies the following criteria for designating a project as “significant”:
All Interstate system projects that occupy a location for more than three days with either intermittent or continuous lane closures, and located within the boundaries of a designated Transportation Management Area (TMA). A TMA is an urbanized area with a population of over 200,000 individuals.
The FHWA Work Zone Mobility and Safety Self-Assessment Guide presents another scheme for categorizing work zone projects based on the expected impact levels. (FHWA Work Zone Mobility and Safety Self-Assessment Guide, Office of Operations, Federal Highway Administration, Washington, DC, 2004.) Under this classification, projects are categorized into Types I, II, III, and IV (see Table 39). Projects classified as Types I and II may require MOT alternative analysis.
In addition, State and local highway agencies have developed their own criteria to define whether a project is “significant.” Some of the typical criteria include:
- Volume/capacity ratio exceeding a specified value.
- Work zone travel time delay exceeding a specified value.
- Queue length exceeding a specified value.
- Reduction in level of service exceeding a specified level.
- Estimated project cost exceeding a specified value.
- Projects based on functional classification.
- Projects on the safety improvement list.
- Worker safety considerations.
- Traffic volume.
- Restrictions on emergency vehicle access.
- Impacts on public/private access.
- Early completion goal.
- Time of work.
- High level of public interest.
- Regional significance.
- Network/corridor level significance.
- Anticipated performance not meeting thresholds.
Table 40 presents a sample of criteria used by the North Carolina DOT for defining significant projects. (NCDOT, Guidelines for Implementation of the Work Zone Safety and Mobility Policy, Draft, 2007.)
The need for an MOT alternative analysis is established based on the significance of the project size and complexity, project duration, traffic volume, and severity of work zone impacts.
Highway agencies typically use partial width reconstruction for low volume, low-impact roads as the baseline MOT strategy where the partial lane closure is in effect during weekday, daytime, or off-peak hours for lane-by-lane construction until the corresponding phase of construction is completed. The closure timings typically are determined based on the latest traffic data, actual field operation experience, and highway capacity calculations. These pre-determined strategies can be effective when the hourly traffic demand does not exceed the work zone capacity. In such cases, the MOT alternative analysis may not be warranted.
When the hourly demand exceeds the agency-estimated work zone capacity values, it is necessary to check whether the projected work zone performance exceeds the allowable targets using quantitative impact analysis. If the projected performance exceeds the allowable targets, a MOT alternative analysis is required to select a strategy that projects work zone performance below the thresholds.
In practice, the requirement for a MOT alternative analysis is waived for non-significant projects with moderate work zone impacts if:
- The hourly traffic demand does not exceed the work zone capacity during lane closure.
- The measured work zone performance does not exceed agency-specified thresholds.
Similar to the approach mentioned above, Figure 12 presents a schematic of lane closure process adopted by the Maryland State Highway Administration (SHA) for arterial highways.
MOT alternative analysis is required for all significant projects where moderate to high impacts are anticipated on work zone traffic and the local area. For such projects, the traffic demand is likely to exceed the lane capacity of the proposed work zone. In such cases, a quantitative analysis is required to model the expected mobility and safety impacts using sketch-planning or deterministic tools. If the estimated impacts do not meet the agency’s thresholds, an alternative analysis should be conducted to select the preferred MOT strategy.
Work zone performance measures are defined, quantifiable, outcome-based conditions or response times that are used to evaluate success of work zone policies, procedures, and performance. Performance measures focus on what to achieve, not how to achieve it. (Work Zone Safety Performance Measures Guidance Booklet, Prepared by American Traffic Safety Services Association (ATSSA), Fredericksburg, VA, 2010.) There are four key measures of work zone performance: mobility (or construction congestion), safety, construction efficiency and effectiveness, and public perception and satisfaction. Table 41 presents a list of performance measures recommended for use in the MOT alternative analysis for each performance category.
At the project level, performance measures are used in evaluating the projected performance of proposed work zone strategies in the pre-construction stages and monitoring the actual performance of those strategies during construction. At the agency level, performance measures are used in evaluating the performance of work zone policies, management strategies, practices, and techniques. In the MOT alternative analysis, the performance measures quantify the impacts outcomes associated with each MOT alternative to determine what would work for the given work zone conditions.
Sources: Highways for Life, Performance Contracting Framework, Prepared by Science Applications International Corporation, Federal Highway Administration, Washington, DC, 2006. Ullman, G. L., R. J. Porter, and G.J. Karkee, Monitoring Work Zone Safety and Mobility Impacts in Texas, Report No. FHWA/TX-09/0-5771-1, Submitted to Texas Department of Transportation, Austin, TX, 2009. Sankar, P., K. Jeannotte, J. P. Arch, M. Romero, and J. E. Bryden, Work Zone Impacts Assessment - An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects, Report No. FHWA-HOP-05-068, Office of Operations, Federal Highway Administration, Washington, DC, 2006.
Performance thresholds set the benchmark of minimum acceptable level for comparing candidate alternatives and further determine what would work best for the given work zone conditions. These values are set by the agency based on the institutional policies and may vary with individual project needs. Table 42 presents a summary of performance thresholds used by various highway agencies for managing work zone impacts.
Sources: Highways for Life, Performance Contracting Framework, Prepared by Science Applications International Corporation, Federal Highway Administration, Washington, DC, 2006. Bourne, J. S. et al, Best Practices In Work Zone Assessment, Data Collection, and Performance Evaluation, NCHRP Project 20-68A Scan 08-04, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, 2010.
Tables 35 and 36 in Chapter 2 provide an array of candidate strategies for work zone management for consideration in the MOT alternative analysis. FHWA’s TMP Matrix77 provides a brief description of the strategies listed in these tables, their pros and cons, what project characteristics may trigger their inclusion in the TMP, and their contributions toward possible improvements in mobility and motorist and worker safety. This information can be used as guidance in the selection of candidate MOT alternatives.
The candidate selection depends largely on the expected mobility and safety impacts, economical impacts to local business and the community, construction phasing and staging, traffic control costs, capacity reduction, feasibility of full lane closure (necessary in some cases), and the distance to feasible detour routes. The findings of the initial assessment conducted in Step 1 should be taken into consideration in identifying the candidate strategies for the MOT alternative analysis. In addition, it is necessary to review the constructability options of the candidate strategies for inclusion in the MOT alternative analysis.
The following factors, used by Maryland SHA for identifying possible work zone constraints, can be used as additional factors for candidate selection:
- Ability to meet performance thresholds.
- Ability to maintain access (businesses, communities, etc.).
- Ability to provide required ramp merge distances.
- Right-of-way impacts.
- Environmental impacts.
- Bridge widths.
- Significant impacts on construction duration.
- Significant impacts to earthwork, retaining walls, pier clearances, profile differences, etc.
- Ability to maintain existing drainage, utility and lighting systems.
- Constructability and construction equipment access.
- Impacts on pedestrian and bicycle facilities.
- Impacts on emergency services (fire, ambulance, police, hospitals).
- Safety (of traveling public and workers).
- Ramp capacity.
- Construction and MOT costs.
Table 43 presents a list of possible strategies for identifying possible candidate strategies based on the preliminary assessment.
In this step, a more rigorous reassessment of work zone impacts and issues, qualitative as well as quantitative, is conducted to facilitate the selection of preferred MOT strategy. The level of detail varies depending on the significance of the impacts and the project itself. More detailed discussion can be found in the FHWA’s guidance on work zone impact assessment. (Sankar, P., K. Jeannotte, J. P. Arch, M. Romero, and J. E. Bryden, Work Zone Impacts Assessment - An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects, Report No. FHWA-HOP-05-068, Office of Operations, Federal Highway Administration, Washington, DC, 2006.)
During the detailed assessment, the performance impacts are quantified for each candidate strategy and qualitative criteria, if any, are reconfirmed. Specific issues pertinent to mobility, safety, construction, and coordination (e.g., right-of-way, utility) are identified and addressed. At this stage, the use of work zone impact analysis tools is considered more suitable for a detailed quantitative analysis. Section 2.9 provides a detailed discussion on the available work zone impact analysis tools, their advantages, and their disadvantages.
Example 3.1: Identifying alternatives for MOT analysis
US 00 serves as a major arterial road connecting the regional industrial hub with the twin metros located in Polk County, District 1. The existing pavement between mileposts 100 and 110 has reached the end of its useful life and needs reconstruction. The route carries significant amounts of commuter and truck traffic. The alternative routes for detour have limited lane capacity and can accommodate only a portion of the work zone traffic volume. This industrial hub is paramount to the economic vitality of the metro region, so long delays are not acceptable. This route also serves a hurricane evacuation route connecting the twin metros to interstate highways. The construction is expected to be scheduled in late summer and early fall seasons.
For the US 00 pavement reconstruction project, the following candidate alternatives can be considered for MOT alternative analysis:
- Alternatives that restrict the operational time of work zones to off-peak hours
- Off-peak full closure.
- Nighttime full closure.
- Weekend full closure.
- Reversible lanes.
- Nighttime partial width closure.
- Weekend partial width closure.
- Work hour restrictions for peak travel.
- Alternatives that divert work zone traffic demand
- Diverting trucks to alternative routes during peak hours.
- Restricting truck travel through the work zone during peak hours.
The MOT alternative analysis involves the consideration of both qualitative and quantitative factors. Recognizing that the possibility for an ideal MOT strategy is impractical, the selection process should focus on identifying an option that more or less meets the project goals. Selecting a meaningful and justifiable option involves weighing both quantifiable performance metrics and policy directives to ensure that both agency and project-specific needs are incorporated in decision making. Decision analysis tools provide a structured, systematic framework for gathering, organizing, and evaluating information to make informed choices.
While any appropriate decision analysis tool can be used, the Kepner-Tregoe (K-T) decision analysis method is recommended here for MOT alternative analysis. (Kepner, C. H., and B. B. Tregoe, The New Rational Manager, Princeton Research Press, Princeton, NJ, 1981.) Not only does this tool allow combining quantitative and qualitative criteria of work zone road user impacts, but it also provides flexibility to make project-specific choices. The steps include:
- Prepare decision statement.
- Define MUST and WANT objectives.
- Assign weights to WANT objectives.
- Identify candidate MOT alternatives.
- Summarize the findings of work zone impact assessment.
- Evaluate alternatives against MUST objectives.
- Evaluate alternatives against WANT objectives.
- Calculate the weighted scores of alternatives.
- Evaluate adverse consequences.
- Select the preferred MOT strategy.
Example 3.2: Illustrating the K-T decision analysis method
The "US 00 Pavement Rehabilitation" example presented in Example 3.1 has been selected for illustrating the K-T decision analysis method.
Step 7.1 Prepare Decision Statement
The K-T decision analysis process begins with a precise statement of what needs to be done and how it will be done. This statement provides the focus for all other steps that follow and sets the limits on the range of alternatives that would be considered in the decision analysis. This statement must be defined consistent with the agency’s work zone related policies and project-specific needs.
The decision statement for the project presented in Example 3.2 is as follows:
The purpose of the decision analysis is to identify the most appropriate strategy for maintaining traffic on US 00 during the reconstruction of the pavement segments between mileposts 100 and 110.
Step 7.2 Define Objectives
Objectives are the decision criteria that describe the required and desired attributes of the resulting choice, and the explicit limits imposed on the decision process. The objectives include:
- MUSTS: These are the mandatory attributes required for an alternative to be considered in the decision process. These attributes are considered mandatory to guarantee a successful decision. Any alternative that cannot comply with a MUST objective is eliminated for further consideration, while those comply with all the MUST objectives qualify as feasible alternatives. The MUST objectives should be measurable, and all MUST objectives are assigned with GO and NO GO options.
- WANTS: These are the desired attributes based on which a preferred alternative is selected from the pool of feasible alternatives (i.e., alternatives that fulfill all the MUST objectives). A mandatory or high-priority objective can be considered as a WANT objective, if that objective is not measurable or a relative assessment is preferred over an absolute GO/NO GO judgment. A MUST objective can also be considered as a WANT objective by rephrasing the objective statement for relative assessment of feasible alternatives. Numerical weights indicating their relative importance are assigned.
In other words, “the MUSTS decide who gets to play, but the WANTS decide who wins.” (Kepner, C. H., and B. B. Tregoe, The New Rational Manager, Princeton Research Press, Princeton, NJ, 1981.)
A list of MUST objectives for Example 3.2 is as follows:
- Maintain a minimum of one lane each direction for work zone traffic during weekdays – Go/No Go
- No lane closure from 7a.m. to 10 a.m. and 4 p.m. to 8 p.m. on weekdays – Go/No Go
- Queue length not more than 0.75 for more than 1 hour – Go/No Go
- Delay time not more than 30 minutes – Go/No Go
- Available detour routes exceed capacity? – Go/No Go
- MOT alternative has no constructability issues – Go/No Go
A list of WANT objectives for Example 3.2 is presented as follows:
- Minimize daily road user costs ($)
- Minimize number of days for project completion
- Minimize traffic control & construction engineering costs ($)
- Minimize length of detour (miles)
- Minimize queue length (lane-miles)
- Minimize average delay time per vehicle (min.)
- Minimize percent motorist traveling at a speed 15 mph less than the posted limit
- Minimize average time to clear a non-injury incidence (min.)
- Maintain emergency services (adjectival ratings—poor, average, good)
- Reduce environmental impacts (adjectival ratings—low, moderate, severe)
Selection of Objectives
One of the commonly cited concerns with decision analysis is the interdependency among objectives. It is a phenomenon where two or more objectives are highly correlated. The presence of interdependence among objectives in decision analysis can produce erroneous or misleading outcomes. Interdependence leads to lead to double counting and tend to weigh heavily toward the interdependent factors, while diminishing the significance of other factors in the analysis. Therefore, it is imperative that a decision analyst screen for interdependency among the objectives and validate them.
For example, consider the list of WANT objectives presented above. The factor “daily road user costs” is highly correlated with the following factors: length of detour, maximum queue length, average delay time, average time to clear non-injury incidence, percent traveling at a speed 15 mph less than the posted speed limit. The factors all contribute to the computation of daily road user cost value. Similarly, the factors “the number of days for project completion” and “traffic control & construction engineering costs” are highly correlated.
One common technique used in screening the interdependency among objectives is sensitivity analysis. A sensitivity analysis can be conducted formally or informally to evaluate the effects of varying one objective (numerical or adjectival) on other objectives and final outcomes. The results of the sensitivity analysis will help to identify correlations among analysis factors. Both the degree of correlation and the logical dependency between the factors should be taken into account while identifying the dependent pairs. The purpose here is to avoid double counting rather than eliminating all correlated factors.
Consider the dependency between two pairs:
- Average delay time vs. daily road user cost. In this case, considering both factors in the analysis will lead to double counting, as the factor “daily road user cost” is a monetized aggregation of various impacts including the factor “average delay time.” Any change in the average delay time will result in a proportional change in the daily road user cost. In such cases, it is suggested that the analyst eliminate the factor “average delay time” or break the factor “daily road user cost” into individual components.
- Average delay time vs. average time to clear a non-injury incident. In this case, the factor “the change in average time to clear a non-injury incidence” also causes a proportional change in the average delay time, and hence is highly correlated. However, considering the probability of a non-injury incident and the importance of clearing the incident, the analyst may prefer to list both factors to emphasize the effectiveness on traffic incident management in MOT alternative selection and distinguish it from other traffic delay control strategies. Therefore, it is imperative to use engineering judgment and experience in selecting the objectives so that the intended purpose of the analysis and the complexity of the problem are not diluted.
The problem of interdependency may occur if one objective is defined at the aggregate/generic level while another is defined at the component/specific level. For example, in the list of WANT objectives presented above, the interdependency between the factor “daily road user cost” and other factors is a result of mixing up the factors from different hierarchical order, as illustrated in Figure 13. This figure presents the relationship between “daily road user costs” and only those delay-related WANT objectives listed in the example. All the factors listed on the left (queue length, average time to clear a non-injury incidence etc) contribute in determining the average delay time, which in turn, is used in the daily road user cost computation.
A modified list of WANT objectives for Example 3.2 is presented as follows:
- Minimize delay costs
- Minimize vehicle operating costs
- Minimize number of days for project completion
- Minimize traffic control and associated construction costs (e.g., shoulder widening, temp bridges)
- Minimize average time to clear a non-injury incidence (min.)
- Maintain emergency services (adjectival ratings—poor, average, good)
- Reduce environmental impacts (adjectival ratings—low, moderate, severe)
Step 7.3 Assign Weights to WANT Objectives
The WANT objectives are not all equally important. Therefore, it is necessary to allocate weights to the items listed in Step 7.2 to reflect their relative priority in the decision. A simple approach is to give the most important criterion a weight of 10 and then assign weights to the rest against that standard.
In this way, each WANT objective is weighted on a scale of 1 to 10 based on its relative importance in the decision process, with 1 indicating “least preferable” and 10 indicating “most preferable” or “equally preferable.” The weights assigned to the WANT objectives should reflect the agency’s policies, results of work zone impact assessment, and project-specific needs. The contribution of the WANT objective to the overall work zone impacts should be taken into account while assigning weights. In addition, the following issues should be evaluated while assigning the weights:
- Too many high weights may indicate unrealistic expectations or a faulty perception of which objectives can guarantee success.
- Too many low weights suggest the possible inclusion of unimportant details in the analysis.
- Biased objectives may produce an ineffective analysis.
Sensitivity analysis can be used in screening such issues.
The following illustrates the assigning of weights to each of the WANT objectives considered in Example 3.2:
|No.||WANT Objective||Assigned Weight|
|2||Vehicle operating costs||8|
|3||Number of days for project completion||10|
|4||Traffic control & associated construction costs ($)||8|
|5||Average time to clear a non-injury incidence (min.)||4|
|6||Maintenance of emergency services (adjectival ratings—poor, average, good)||6|
|7||Environmental impacts (adjectival ratings—low, moderate, severe)||3|
Step 7.4 Identify Candidate MOT Alternatives
Identify all potential alternatives to be evaluated and measured as MUST and WANT objectives. The viable alternatives that could succeed in identifying the preferred MOT strategy are listed herein. Use the alternatives identified in Step 5 as candidate alternatives for decision analysis. No attempt is made in this step to evaluate these alternatives, only to list them.
The candidate alternatives for Example 3.2 are as follows:
Alternative A. Daytime partial lane closure –closed between 7 a.m. and 5 p.m.
Alternative B. Nighttime partial lane closure –closed between 8 p.m. and 6 a.m.
Alternative C. Nighttime partial lane closure –closed between 9 p.m. and 7 a.m.
Alternative D. Nighttime full lane closure –closed between 9 p.m. to 7 a.m.
Alternative E. Truck traffic diverted through detour routes during peak hours.
Step 7.5 Summarize the Findings of Work Zone Impact Assessment
A detailed work zone impact assessment for each candidate alternative should be done to evaluate both MUSTs and WANTs. Use the findings of the preliminary and detailed impact assessments conducted in Step 1 and Step 5, respectively, for evaluation. The assessment findings must be summarized for each alternative against the objectives.
The following summarizes the impact assessment findings of all alternatives against the MUST objectives considered in Example 3.2:
|MUST Objective||Alternative Evaluation|
(Calculated for the selected detour route.)
(Weighted average for both mainline and detour routes. )
(Calculated for the selected detour route.)
(Weighted average for both mainline and detour routes.)
The following summarizes the impact assessment findings of all alternatives against the WANT objectives considered in Example 3.2:
|WANT Objective||Alternative Evaluation|
Step 7.6 Evaluate Alternatives against MUST Objectives
Evaluate all available alternatives against each of the MUST objectives identified in the earlier step. Any alternative is eliminated from further consideration if it fails to satisfy one or more of the MUST objectives; only those satisfying all the objectives are considered as feasible alternatives.
For Example 3.2, the results obtained from the evaluation of alternatives against MUST objectives are presented as follows:
Alternatives A and E are eliminated.
Alternatives B, C and D qualify as feasible alternatives
Based on the evaluation results, Alternatives A and E are eliminated from further consideration, as these alternatives did not satisfy all the required attributes. Alternatives B, C, and D are carried into the next step.
Step 7.7 Evaluate Alternatives against WANT Objectives
In this step, each alternative is assigned with a score of 1 to 10 against each WANT objective based on how well the alternative meets that objective. This step involves assessing each alternative individually against each WANT objective and comparing the alternatives with each other against each WANT objective.
For Example 3.2, the results obtained from the evaluation of alternatives against WANT objectives are presented as follows:
|WANT Objective||Weight||Alternative Score|
Step 7.8 Calculate the Weighted Scores of Alternatives
The weighted score of each feasible alternative should be computed to determine the relative performance of the alternatives. The weighted score is the score of an alternative multiplied by the weight of the WANT objective to which the score refers. For example, the weight of the objective “length of detour” is 7, and the score of Alternative D against this objective is 2. Therefore, the weighted score of Alternative D on that objective is 14. For each alternative, all the weighted scores are added up to calculate the total weighted score for that alternative.
The total weighted score of an alternative indicates how well an alternative stack up against each of the other alternatives on overall performance against WANT objectives. In other words, the total weighted scores indicate the comparative performance of the alternatives.
For Example 3.2, the individual and the total weighted scores of each feasible alternative are as follows:
|WANT Objective||Alternative Score|
|Total weighted score||373||367||426|
In this example, Alternative D is considered as the tentative choice.
Step 7.9 Evaluate Adverse Consequences
After the completion of alternative evaluation using MUST and WANT objectives, the feasible alternatives should be evaluated against potential risks identified in the work zone impact assessment. The objective of this step is to understand the consequences of selecting an alternative by evaluating them separately. No comparative assessment is made as to identify which alternative is more likely to produce adverse consequences than other alternatives.
The risk assessment begins with the tentative choice (i.e., the alternative with the highest total weighted score). For this alternative, the probability of the occurrence of an adverse consequence is rated on a scale from “Low” to “High,” with a rating of “Low” indicating “an unlikely event” and “High” indicating “a most probable event.” The severity of the impact (i.e., performance of an alternative under that event) is assessed and rated on a similar scale, with a value of “Low” indicating “inconsequential” and “High” indicating “very severe.” This evaluation is repeated for each alternative that passes all the MUST objectives.
The likelihood of the adverse events occurring and the performance of an alternative under these situations were rated as probability and severity ratings, respectively. An alternative is considered a high-risk choice if it has at least one potential adverse consequence that is considered both highly probable and very severe, while those alternatives with low probability and low-severity consequences are considered low-risk choices.
For Example 3.2, three potential risks were considered:
- Event of flooding.
- High-severity crashes (involving multiple crashes and longer incidence time).
- Event of an emergency evacuation due to hurricanes.
The evaluation of adverse consequences for the MOT alternatives B, C, and D considered in the example are shown as follows:
Based on this evaluation, the adverse consequences of implementing Alternative B or Alternative C are deemed less significant, and therefore, selected for further consideration. Implementing Alternative D is more likely to create problems and confusion during emergency evaluation for the following reasons:
- An emergency mass evacuation is more probable during late summer and early fall (the period when the construction is expected to be scheduled).
- Failure to remove full closure traffic controls within a shorter period of time could be problematic.
- Local users are more likely to avoid this route, assuming that the full closure would still be in place, thus resulting in network-level bottlenecks and confusion.
Alternative D is considered as a high-risk choice, while Alternatives B and C are deemed low-risk choices.
Step 7.10 Select the Preferred MOT Strategy
The total weighted score and the results of adverse consequence evaluation are summarized for each alternative from steps 7.8 and 7.9.
High-risk choices can be eliminated from further consideration. Other alternatives are then ranked based on their weighted scores. The alternative with the lowest rank is selected as the preferred MOT strategy.
Alternatively, high-risk choices may be enhanced with additional measures to mitigate the impacts of an adverse consequence. These enhancements may incur additional costs and may impact work zone performance. Therefore, these revised choices may need to be re-evaluated through the decision analysis process with other alternatives. Engineering judgment should be exercised in making any decisions relating to eliminating, reviewing, and/or re-evaluating high-risk choices.
In Example 3.2, Alternative D is identified as a high-risk choice despite its highest total weighted score. However, a decision was made to review Alternative D for possible enhancements rather than eliminating it. Since only nighttime full closures are made under Alternative D, there was scope for addressing the concerns related to emergency evacuation with no requirement for re-evaluation. Risks associated with emergency evacuation can be mitigated effectively through improvements in public awareness and motorist information strategies. The cost of implementing mitigation measures is marginal and can be justified with road user cost savings.
For Example 3.2, the recommended MOT strategy is Alternative D with additional public awareness and motorist information strategies.
|Alternative||Description||Total Weighted Score||Adverse Consequence||Rank|
|A||Daytime partial lane closure –closed between 7 a.m. to 5 p.m.||Eliminated||–||–|
|B||Nighttime partial lane closure –closed between 8 p.m. to 6 a.m.||373||Low Risk||2|
|C||Nighttime partial lane closure –closed between 9 p.m. to 7 a.m.||367||Low Risk||3|
|D||Nighttime full lane closure –closed between 9 p.m. to 7 a.m.||426||High Risk
|E||Truck traffic diverted through alternative detour routes during peak hours.||Eliminated||–||–|
Appendix A provides a worksheet for performing K-T decision analysis for MOT strategy selection.
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