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Strategies for Work Zone Transportation Management Plans (2020)

Chapter: Chapter 13 - Framework for Evaluation of Work Zone Strategies

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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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Suggested Citation:"Chapter 13 - Framework for Evaluation of Work Zone Strategies." National Academies of Sciences, Engineering, and Medicine. 2020. Strategies for Work Zone Transportation Management Plans. Washington, DC: The National Academies Press. doi: 10.17226/25929.
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220 This section describes various methods by which work zone strategies are evaluated. 13.1 Typical Work Zone Crash Characteristics Increased crash risks at a given work zone are a combination of temporary changes in geo­ metrics and influences related to work activity. Drivers can be distracted by ongoing construction activities behind barriers, moving equipment, construction access and egress, and lane closures that require drivers to maneuver around the closure or shift laterally. When work activity is occurring and travel lanes are temporarily closed, the risk of a crash for an individual motorist traveling through the work zone can increase by as much as about 66 percent during the day and 61 percent at night, compared with the crash risk expected to exist at a particular location (Ullman et al. 2008). The actual change in crash risk will vary substantially between projects, even when stratified on the basis of time period (daytime or nighttime) and work condition (no work activity, active work without lane closures, or active work with lane closures). Crashes that occur in nighttime work zones are not necessarily more severe than those that occur in similar daytime work zones, although differences do exist in the types of crashes. Generally, the increase in crash risk is higher for property­damage­only crashes than for injury and fatal crashes, regardless of whether the work is performed during the day or at night. The only exception is for intrusion crashes during nighttime, which have a greater percentage of injury and fatal crashes (Ullman et al. 2008). Crashes involving rear­end collisions are one of the most common crash types in work zones and typically increase as a function of AADT in both daytime and nighttime periods; the percentages are substantially lower in the nighttime periods. However, the percentage of rear­end collisions increases noticeably during daytime work activity on low­ to moderate­volume roadways, but not on higher­volume roadways. Nevertheless, the benefit of working at night, compared with doing the work during the day, extends across all AADTs, but it is much greater at higher AADTs. Several strategies have the potential to substantially lower the increased crash risk resulting from work zones (Appendix A). Strategies that appear to offer the greatest potential for crash­ risk reduction include the following: • Practices to reduce the number and duration of work zones (i.e., within a specific project limit). • Project coordination with adjacent projects on the same or nearby corridors to avoid conflicts (i.e., rerouted traffic to closed or reduced capacity routes or conflicting signs or messages). • Use of full directional roadway closures with median crossovers or detours. • Use of time­related contract provisions to reduce construction duration. • Appropriate work activities on high AADT roads (i.e., those that require temporary lane closures) being moved to nighttime hours. C H A P T E R 1 3 Framework for Evaluation of Work Zone Strategies

Framework for Evaluation of Work Zone Strategies 221 • Use of demand­management strategies to reduce volumes through work zones during the day. • Use of enhanced or automated traffic law enforcement (or both). 13.2 Expected Effects of Work Zones on Crashes It would be beneficial for work zone designers and others to be able to predict the safety consequences of their proposed work zone designs and management decisions before imple­ menting them in the field. The following are examples of ways to use work zone crash estimates: • Quantify the safety­related benefits of completing the work faster (i.e., accelerated contract incentives). • Estimate the expected effects of safety countermeasures contemplated for use in the work zone as part of the TMP. • Predict the differences in safety effects of alternative work zone design options (i.e., narrowed or closed lanes, closed shoulders, ramp closures, and complete closures). 13.3 Work Zone Safety-Related Data Analysis Depending on the actions being considered, methods are needed to estimate the number of crashes expected to occur in a work zone and the incremental change in crashes resulting from different work zone features. These methods vary in the amount of data and level of effort required, as well as in the level of accuracy to be achieved. Because of the relatively short duration of most construction projects (versus 3–5 years of after data in a typical before/after study at a permanent location) and relatively few crashes, there may not be sufficient work zone crash data to make statistically significant conclusions. Poor­quality data in the data set can result in misleading or incorrect conclusions. The number of variables that can affect the analysis of crashes within work zones can make isolating a single vari­ able difficult. Factors related to analyzing safety­related data in work zones include the following: • Frequent changes to the configuration of a work zone make it difficult to track or assign an exact work zone setup to a particular crash. • The number of work zone crashes per project is relatively small and typically does not follow a normal distribution. • Work zone strategies that encourage trip diversion may have significantly different pre­ and post­traffic volume, and the analysis may provide misleading conclusions. • Some crashes within the work zone limits may have been caused by non–work zone char­ acteristics (e.g., driver impaired or speeding), meaning the work zone may not have been a contributing factor or an indirect cause. 13.3.1 Before and After Crash Data Analysis Several considerations when conducting a before and after study of crash data within the work zone may affect the validity of the evaluation. These considerations include the following: • Regression-to-mean bias. A project corridor may have a high number of crashes imme­ diately before the work zone period. This may be an abnormal condition in which the site may experience fewer crashes during construction, regardless of the deployment. A simple before and after comparison is likely to result in an overestimation of the work zone strategy effect. Analysts can use more robust statistical analysis methods such as a Bayesian approach to minimize the problem.

222 Strategies for Work Zone Transportation Management Plans • Other explanatory factors after the work zone strategy deployment. Increased law enforce­ ment may cause drivers to reduce speed or be less aggressive, which potentially reduces crashes. If the before and after study does not take this relationship between increased law enforcement presence and reduced crashes into account, then the benefits of the work zone deployment can be overestimated. • Trends in the value of MOEs over time. If the decrease in crashes in the after data is a result of a long­term trend and not a result of the work zone deployment, then the evaluation will suffer from what is known as a maturation threat to validity. • Random data fluctuations. According to FHWA, “Crashes are random events that naturally fluctuate over time at any given site. If you consider a short­term average crash frequency, it may be significantly higher or lower than the long­term average crash frequency. The crash fluctuation over time can make it difficult to determine whether changes in observed crash frequency are due to changes in site conditions or natural fluctuations” (Herbel, Laing, and McGovern 2010). This threat to evaluation validity is known as instability. 13.3.2 Crash Rate Calculation Crash rate is a measure that can be applied to work zones to monitor trends in crashes using either real­time or lagging data. Crash rate analysis typically uses exposure data in the form of traffic volumes or roadway mileage. As Table 13.1 shows, crash rates are calculated by dividing the number of crashes by a normalizing factor. Such rates can be compared with preconstruction values to determine whether safety hazards exist and whether analysts need to consider modifications to the work zone. The benefit of crash rate analysis is that it provides a more effective comparison of similar locations with safety issues than analyzing crash frequency alone. In a situation when traffic volumes have changed significantly during the work zone, the crash rate calculation allows practitioners to take this into account. One way to calculate the crash rate for road segments is = × × × × 100,000,000 365 R C N V L Equation 1. Crash rate for road segment. where R = Crash rate for the road segment expressed as crashes per 100 million VMT; C = Total number of crashes in the study period; N = Number of years of data (or fraction of a year); V = Number of vpd (both directions); and L = Length of the roadway segment in miles. Normalizing Factors Example Measures Time Crashes per month Exposure Crashes per 1,000 vehicles traveling through the work zone Crashes per vehicle hours of travel time through the work zone Crashes per 100 million VMT through the work zone Distance Crashes per mile NOTE: VMT = vehicle miles traveled. Table 13.1. Examples of crash rate normalizing factors.

Framework for Evaluation of Work Zone Strategies 223 For example, a particular work zone is being assessed with the following values: C = 90 crashes over the past 1 year within this work zone, N = 1 year of data, V = 35,000 vpd, and L = 8 miles. The resulting segment crash rate (equation 2) would be 88.1 crashes per 100 million VMT. 100,000,000 90 365 1 35,000 8 88.1 100R crashes per million VMT= × × × × = Equation 2. Example crash rate calculation for road segment. Depending on the details of crash­reporting methods and crash history along the project corridor, a value of 88.1 crashes per 100 million VMT may or may not be cause for additional study. The most appropriate use of this crash rate is to determine the relative safety of the work zone in comparison with the pre–work zone condition and with other work zones that have similar characteristics. If a DOT has access to real­time crash reports, it can improve safety in its work zones even further by modifying active work zones based on reported work zone crashes. 13.3.3 Crash Modification Factors CMFs can be employed to estimate the incremental change in crashes related to alter native work zone features being considered, similar to procedures found in the HSM. A CMF is a multiplicative factor used to indicate how a particular condition or feature increases or decreases the number of crashes expected from base conditions. A CMF of 1.0 indicates that the feature has no incremental effect on crash risk. A CMF less than 1.0 indicates that the feature reduces crash risk, and a CMF above 1.0 indicates that the feature increases crash risk relative to base conditions. When multiple features are present, several CMFs are multiplied to arrive at the estimate of the expected change in crashes. Although many CMFs have been developed for many different permanent roadway features in recent years, only a few work zone­specific CMFs are currently available. In the absence of CMFs developed specifically for work zone features, the only available option is to use those that exist for permanent roadway features. In these cases, practitioners apply engineering judgment when interpreting the results of the analysis. The HSM provides limited information on CMFs for practitioners to use in work zones. The work zone elements addressed in the HSM include the duration (number of days) and length (miles) of freeway work zones. Equations 3 and 4 are based on research that considered work zone durations from 16 to 714 days, work zone lengths from 0.5 to 12.2 miles, and freeway AADTs from 4,000 to 237,000 vpd (Khattak, Khattak, and Council 2002). The base condition of the CMFs (i.e., the condition in which the CMF = 1.00) is a work duration of 16 days and 0.51 miles. The standard errors of the CMFs are unknown. Duration. Equation 3 provides expected average crash frequency for increasing work zone duration above the base condition (CMF = 1.0) of 16 days. ( )= + ×1.0 % 1.11 100 CMF increase in duration all Equation 3. Average crash frequency for increasing work zone duration (days).

224 Strategies for Work Zone Transportation Management Plans where CMFall = crash modification factor for all crash types and all severities in the work zone; and % increase in duration = the percentage change in the duration (days) of the work zone. Length. Equation 4 provides expected average crash frequency for increasing the work zone length above the base condition (CMF = 1.0) of 0.51 mi. ( )= + ×1.0 % 0.67 100 CMF increase in length all Equation 4. Average crash frequency for increasing work zone length (mi). where CMFall = crash modification factor for all crash types and all severities in the work zone; and % increase in length = the percentage change in the length (mi) of the work zone. 13.4 Work Zone Crash Estimation and Crash Cost Analysis NCHRP Research Report 869 (Ullman et al. 2018) describes the following two methods for estimating work zone crashes and crash costs: 1. Applying an overall WZCMF to a pre–work zone baseline estimate of crashes expected on the roadway segment where the work zone will occur. 2. Using a general safety performance function (SPF) that has been created using work zone­ specific data. A brief description of both methods follows. 13.4.1 Method 1. Using Pre–Work Zone Crash Estimates and an Overall WZCMF The preferred approach for developing planning­level work zone crash estimates is to apply an overall generic WZCMF to the pre–work zone baseline crash estimate for the roadway segment. Pre–work zone crash estimates would generally come from an SPF calibrated to the particular roadway segment using methods contained in the HSM or in state­calibrated crash­prediction models. However, if those data are not available, other estimation methods may be used. For example, work zone analysts could use the last 3–5 years of crashes occurring along the roadway segment along with yearly AADT values to determine a weighted yearly average of crashes. An overall WZCMF for freeways and Interstate facilities from a multistate data set of four­ and six­lane freeway and Interstate work zones was developed as part of NCHRP Research Report 869 (Ullman et al. 2018). The CMF is based on a ratio of pre– and during–work zone SPFs developed for those roadway segments. Equation 5 gives the ratios of those SPFs: = = ( ) ( ) ( ) ( ) − + − + − + − + 4­lane Facility 6­lane Facility e e e e 4­lanes 10.036 1.164 ln AADT 11.231 1.248ln AADT 6­lanes 9.987 1.164 ln AADT 12.318 1.344 ln AADT WZCMF WZCMF Equation 5. WZCMFs for four- and six-lane freeway and Interstate work zones.

Framework for Evaluation of Work Zone Strategies 225 To compute the total number of crashes expected during a work zone, multiply the per mile number of crashes normally occurring on the roadway segment each year by the duration of the work zone and calculate the overall WZCMF for the AADT of the roadway segment. As Equation 6 shows, if a crash rate is used, then the rate is first multiplied by the length of the project. ( ) ( ) ( )=         ­ . 12 Expected WZ Crashes Non WZ Crashes Mile Year Project Length WZ Duration Mo WZCMF Equation 6. Total number of crashes expected during a work zone. 13.4.2 Method 2. Work Zone-Based SPFs If no good data exist for the normal crash frequency on the section of freeway or Interstate where a work zone will be placed, a work zone engineer can use an SPF to develop a planning­ level estimate of crashes expected during the work zone. NCHRP Research Report 869 (Ullman et al. 2018) used the multistate database of work zones performed on four­ and six­lane Interstates and freeways to develop the following two predictive functions of the total number of work zone crashes expected to occur based on work zone length, work zone duration, and overall roadway AADT (equations 7 and 8). = × × ( )− +10.036 1.164 lnNumber of work zone crashes expected L n e AADT Equation 7. Crashes expected to occur on four-lane freeway and Interstate work zones. = × × ( )− +9.987 1.164 lnNumber of work zone crashes expected L n e AADT Equation 8. Crashes expected to occur on six-lane freeway and Interstate work zones. where L = length of work zone in miles and n = number of years the work zone will require (or number of months/12). The functions were developed with the following work zone conditions: • Pavement width of 40 ft in each direction for four­lane segments and 52 ft in each direc­ tion for six­lane segments (equal to 12­ft lanes, a 6­ft inside shoulder, and a 10­ft outer shoulder). • No lane shifts present. • No lane closures present. • Median width of 60 ft, inclusive of inside shoulder width of 6 ft in both directions. • No longitudinal barriers present. • AADTs ranging between 5,000 and 70,000 vpd on the four­lane segments. • AADTs ranging between 50,000 and 150,000 vpd on the six­lane segments. Examples 1 and 2 in the following sections are based on the work zone condition described above. NCHRP Web-Only Document 240: Analysis of Work Zone Crash Characteristics and Counter- measures (Ullman et al. 2018) provides additional details regarding the development of these models.

226 Strategies for Work Zone Transportation Management Plans 13.4.3 Example 1. Computing an Expected Crash Rate per Month during Construction A work zone engineer plans to monitor crashes occurring during a 2­year, 5­mi Interstate­ widening construction project. The engineer will compare monthly crashes to determine if they are increasing beyond what should be expected for the work zone setup. The roadway has the following characteristics: • Rural four­lane Interstate facility (12­ft lanes, 6­ft inside shoulder, 10­ft outside shoulder, wide median). • Traffic volume on the facility is 45,000 vpd during Year 1 of the project and 50,000 vpd during Year 2. • Based on a calibrated SPF developed by the DOT, the normal non–work zone crash rate on this facility is estimated to be 7.4 crashes per mile in Year 1 and 7.9 crashes per mile in Year 2. Step 1. Calculate the WZCMF (Years 1 and 2), assuming that good pre–work zone crash data exist. Step 2. Use the WZCMF to calculate the work zone expected crashes, work zone crash rate, and project length (Years 1 and 2, equation 9). Step 3. Sum Year 1­ and Year 2­expected crashes to determine total crashes (equation 10). =     = =     = ( ) ( ) ( ) ( ) − + − + − + − + WZCMF 1.34 WZCMF 1.33 4­lanes, year 1 10.036 1.164 45,000 11.231 1.248 45,000 4­lanes, year 2 10.036 1.164 50,000 11.231 1.248 50,000 e e e e ln ln ln ln Equation 9. Crashes expected to occur during the project duration. In this example, the expected crash rate each year follows: ( ) ( ) ( ) ( ) ( ) ( ) =     = =     = = + =( ) Expected Work Zone Crashes 7.4 5 mi 1 1.34 49.58 crashes Expected Work Zone Crashes 7.9 5 mi 1 1.33 52.54 crashes Expected Work Zone Crashes 49.58 52.54 102.12 crashes year 1 year 2 year 1 and 2 Total crashes mi yr year crashes mi yr year Equation 10. Expected crash rate per year. The work zone engineer can divide by 12 (number of months in year) to get a month­by­ month crash estimate per year. If a more finite­period analysis is needed, the engineer can apply seasonal factors to the AADT factors and develop and apply WZCMFs to determine the crashes expected each month of each year. Monthly crashes can be compared directly as well as cumula­ tively. Significant variations between actual and expected crashes per time period might indicate that a safety issue exists at the site and additional investigation is needed. As Figure 13.1 shows, an increase in the number of crashes is observed starting in month 7. If it is determined that the increase in crashes is significant enough, then the work zone engineer can initiate a more in­depth review to determine potential reasons for the increase. The potential reasons may be that the project has had a major traffic switch, work activities have involved more frequent deliveries, or poor weather conditions occurred during this time.

Framework for Evaluation of Work Zone Strategies 227 If good non–work zone crash data are not available for the segment, then the work zone engineer can apply a previous work zone SPF for four­lane facilities (equation 11). The compu­ tations would be as follows: ( ) ( ) ( ) ( ) ( ) ( ) = = = = = + = ( ) ( ) ( ) − + − + Expected Work Zone Crashes 5 mi 1 57.11 crashes Expected Work Zone Crashes 5 mi 1 64.56 crashes Work Zone Crashes Expected 57.11 64.56 121.67 crashes year 1 10.036 1.164 45,000 year 2 10.036 1.164 50,000 year 1 and 2 Total year e year e ln ln Equation 11. Expected crash rate using SPF. The work zone SPF estimate of 121.67 crashes over the 2­year project (5.07 crashes per month) is approximately 19.1 percent higher than what was computed using the calibrated pre–work zone crash rates and the overall WZCMF. As Figure 13.2 shows, in using the work zone SPF, Cu m ul ati ve N um be r o f C ra sh es to D at e Months of Project Figure 13.1. Expected versus actual crashes using Equation 9 WZCMF. Cu m ul ati ve N um be r o f C ra sh es to D at e Months of Project Figure 13.2. Expected versus actual crashes using the work zone SPF and CMF.

228 Strategies for Work Zone Transportation Management Plans the work zone engineer may conclude that crashes were not excessive relative to expectations. The difference in results shown in Figure 13.2 using both methods is another reminder of the importance of engineering judgment when interpreting and using planning­level estimates. 13.4.4 Example 2. Estimating the Effect of Accelerated Construction on the Expected Number of Work Zone Crashes and Savings A DOT is contemplating including contract incentives in a bid package to reduce the project duration and is trying to determine the savings, if any. By using traditional methods, the project would take 2 years to complete; however, if the duration is reduced to 18 months (i.e., acceler­ ated construction) what would be the project savings? The DOT will first calculate the non–work zone CMF to serve as a baseline for comparison (equation 12). The roadway has the following characteristics: • Project is 6 mi long. • It is an urban six­lane freeway facility. • The traffic volume on the facility is expected to be approximately 120,000 vpd for Year 1 of the project and 140,000 vpd for Year 2 of the project. • The freeway has 12­ft lanes, 6­ft inside shoulders, and 10­ft outside shoulders. • The total crash density on this section of freeway is 34.8 crashes per mile per year before construction based on 3 years of historical data. Traffic volumes during those years averaged 115,000 vpd (similar to what is expected for Year 1 of the project). Non­Work Zone Crash Rate 34.8 120,000 115,000 36.31 crashes per mile per year Non­Work Zone Crash Rate 34.8 140,000 115,000 42.36 crashes per mile per year year 1 year 2 crashes mi yr crashes mi yr =         = =         = Equation 12. Year 1 and 2 work zone crash rate. The DOT does not have a normal non–work zone expected crash frequency for the road­ way for each year of the project. Consequently, it will be necessary to estimate the normal pre–work zone crash frequency for each of the 2 years of the project based on the data avail­ able (equation 13). Because the only data available for use are the historical crash rate for the roadway segment associated with a lower AADT than that anticipated during the project, the DOT would first factor the crash rate for the 2 years of the project using the following ratio of AADT numbers: WZCMF 1.253 WZCMF 1.219 6­lanes, year 1 9.987 1.164 120,000 12.318 1.344 120,000 6­lanes, year 2 9.987 1.164 140,000 12.318 1.344 140,000 e e e e ln ln ln ln =     = =     = ( ) ( ) ( ) ( ) − + − + − + − + Equation 13. Work zone CMFs. This factoring process assumed a linear relationship between crashes and AADT, which is often not true. However, in the absence of local SPFs, it is considered to be a plausible planning­level assumption. Once the DOT has a predicted non–work zone crash rate for each year, WZCMFs are then computed for each of the 2 years of the project based on the expected traffic volumes (equation 14).

Framework for Evaluation of Work Zone Strategies 229 The total number of crashes expected for each alternative is calculated using the results of equation 13 as follows, assuming 24 months (Years 1 and 2 summed) for Alternative 1: ( ) ( ) ( ) ( ) ( ) ( ) =     = =     = = + =( ) Expected Work Zone Crashes 36.31 6 mi 1 1.253 272.97 crashes Expected Work Zone Crashes 42.36 6 mi 1 1.219 309.82 crashes Expected Work Zone Crashes 272.97 309.82 582.79 crashes ALT 1 year 1 ALT 1 year 2 ALT 1 year 1 and 2 Total crashes mi yr year crashes mi yr year Equation 14. Number of crashes expected for Alternative 1. For Alternative 2, the expected number of crashes for Year 1 of the project would remain the same as Alternative 1. For the second year, the first 6 months would be at the expected work zone crash rate and the second 6 months would be at the non–work zone crash rate (required to complete Year 2), as shown in equations 15 and 16: ( ) ( ) ( )=         +        = = + =( ) Expected Work Zone Crashes 42.36 6 12 6 mi 1.219 42.36 6 12 6 mi 281.99 crashes Expected Work Zone Crashes 272.97 281.99 554.96 crashes ALT 2 year 2 ALT 2 year 1 and 2 Total crashes mi yr mo mo yr crashes mi yr mo mo yr Equation 15. Number of crashes expected for Alternative 2. = − =−Expected Work Zone Crashes 582.79 554.96 27.83 crashesALT 1 ALT 2 Equation 16. Difference between Alternatives 1 and 2. Reducing the duration of the project by 6 months would be expected to result in 27.83 fewer crashes over the non­accelerated project schedule. The DOT can now apply comprehensive crash cost numbers to estimate the road­user safety cost savings that could be attributed to this reduction. Assuming a crash severity distri­ bution on the facility similar, as Table 13.2 shows, to typical crash cost values recommended in the HSM, reducing the project duration would be estimated to yield nearly $1,332,592 in crash cost savings. This would be in addition to any other savings that might also be achieved (i.e., travel time, freight, and emissions). Crash Severity Level Proportional Distribution of Crash Severities Proportion of the 27.83 Crashes Reduced Average Crash Costa Crash Costs Saved If Project Is Accelerated Fatality (K) 0.005 0.13915 $4.509,991 $627,565.25 Disabling injury (A) 0.018 0.50094 $242,999 $121,727.92 Evident injury (B) 0.088 2.44904 $88,875 $217,658.43 Possible injury (C) 0.136 3.78488 $50,512 $191,181.86 Property damage only (PDO) 0.753 20.95599 $8,325 $174,458.62 Total 1.000 27.83 n.a. $1,332,592.08 NOTE: aCrash costs in the Highway Safety Manual, 1st ed., updated to 2016 dollars. n.a. not applicable. Table 13.2. Estimated crash cost savings if project duration can be reduced, Example 2.

230 Strategies for Work Zone Transportation Management Plans 13.5 Evaluation of Alternative Work Zone Design Using Alternative CMFs Work zone designers developing construction plans have options for accommodating traffic through the various phases or stages of the project. These alternatives can include factors such as whether to close lanes or shoulders, use narrower lanes, close ramps, reduce acceleration or deceleration lane lengths, and deploy together with various technologies (e.g., EQWSs, DLMs). When designers must make decisions, it is useful for them to know the differences in expected crashes among these alternatives. The steps are as follows: Step 1. Define the work zone alternatives for which the expected safety effects are to be compared. Step 2. Determine the availability and suitability of CMFs. Step 3. Obtain baseline crash estimates that will be used to evaluate each alternative. Step 4. Multiply the selected CMFs for each work zone alternative with their appropriate base­ line crash estimates. Step 5. Compute crash estimate differences among the alternatives. For example, to alert drivers of downstream queues, a DOT is contemplating using the EQWS during an 8­month bridge repair project over an Interstate facility. The contractor will institute nighttime lane closures (7:00 p.m. to 6:00 a.m.) on the Interstate to perform the work and will work 5 nights per week. The Interstate serves 70,000 vpd in this area, and queues are expected to develop each night of work and can grow to up to 7 mi. Normally, this section of Interstate records 20.4 crashes per mile per year, 50 percent of which occur during the hours when the work is scheduled. The DOT wishes to estimate how many crashes might be prevented if the EQWS is incorporated into the project. The DOT performs the following analysis. Step 1. Define work zone alternatives to be compared. Alternative 1. Perform the nighttime lane closures over the 6­month project without EQWS. Alternative 2. Install EQWS at the beginning of the project to warn of queued traffic condi­ tions downstream. Step 2. Determine availability and suitability of CMFs for alternatives. A CMF for working at night with one or more lanes closed is 1.61 (Table 13.3). For Alter­ native 2, a CMF describing the effect of the EQWS is 0.56 with traffic queues (Table 13.4). Crash Severity Level CMF Nighttime Daytime Work Zone Active with Temporary Lane Closures PDO Crashes 1.748 1.808 Injury and Fatal Crashes 1.423 1.455 All Crashes Combined 1.609 1.663 Work Zone Active without Temporary Lane Closures PDO Crashes 1.666 1.398 Injury and Fatal Crashes 1.414 1.174 All Crashes Combined 1.577 1.314 Work Zone Inactive without Temporary Lane Closures PDO Crashes 1.330 1.196 Injury and Fatal Crashes 1.114 1.020 All Crashes Combined 1.237 1.127 NOTE: CMF = crash modification factor; PDO = property damage only; WZCMF = work zone crash modification factor. SOURCE: Ullman et al. (2008). Table 13.3. Freeway WZCMFs.

Framework for Evaluation of Work Zone Strategies 231 Work Zone Condition Work Zone Application CMF Volume Range Quality Crash Severity Stationary Police Enforcement DA 0.585 <125,000 M A Automated Speed Enforcement P 0.83 NS H F/I Speed Feedback Display P 0.54 NS H A Transverse Rumble Strips (Nighttime) (Queues Not Present/Queues Present) DA 0.89/0.397 55,000– 110,000 H A End Queue Warning System (Nighttime) (Queues Expected/Queues Present) DA 0.559/0.468 55,000– 110,000 M A Increase Shoulder Width (Inside/Outside) by 1 ft DA 0.97/0.948 NS M A Change Median Width 20 to 10 ft. Conversion (Rural/Urban Freeway) P 1.16/1.12 <120,000/ <131,000 H NS Reduce Lane Width 12 to 11 ft. (Divided Rural Multilane Roadway) P 1.03 >2,000 H A Reduce Lane Width 12 to 10 ft. (Divided Rural Multilane Roadway) P 1.15 >2,000 H A Reduce Lane Width 12 to 9 ft. (Divided Rural Multilane Roadway) P 1.25 >2,000 H A Reduce Shoulder Width 6 to 4 ft. (Rural Two-Lane Roadway, Undivided Multilane Roadway) P 1.15 >2,000 H A Reduce Shoulder Width 6 to 2 ft. (Rural Two-Lane Roadway, Undivided Multilane Roadway) P 1.3 >2,000 H A Reduce Shoulder Width 6 to 0 ft. (Rural Two-Lane Roadway, Undivided Multilane Roadway) P 1.5 >2,000 H A Variable Speed Limit P 0.92 NS H A Crossover Work Zone Left-Hand Merge DA 1 NS M A and Downstream Shift DA 0.54 20,000– 35,000 L A Reduce Speed Limit (10 mph/15–20mph) Q 0.96/0.94 NS M–H A Safety Edge on Temporary Roadway P 0.94 <19,000 H A NOTE: WZCMF = work zone crash modification factor; CMF = crash modification factor; DA = direct application; P = possible; Q = questionable; H = high quality of CMF; M = medium quality of CMF; L = low quality of CMF; A = all; F/I = fatal/injury; NS = not specified. SOURCE: NCHRP Research Report 869 (Ullman et al. 2018). Table 13.4. Available WZCMFs.

232 Strategies for Work Zone Transportation Management Plans Step 3. Obtain appropriate baseline crash estimate for applying CMFs. The work zone baseline crash estimate Alternative 1 is computed as in equation 17: Baseline Crashes 20.4 crashes mi yr 7.0 mi 8 mo 12 mo yr 5 days wk 7 days wk 0.5 night crashes all crashes 1.61 54.74 crashes ( ) ( ) ( )=                 = Equation 17. Baseline crash estimate for applying CMFs. Step 4. Apply CMFs for each alternative to baseline crash estimate. For Alternative 2 (with EQWS), the baseline crash estimate (Alternative 1) must be multiplied by the work zone queue warning CMF, as in equation 18, to compute the expected number of crashes: Crashes 54.74 crashes Crashes 54.74 0.56 30.65 crashes ALT 1 ALT 2 = = × = Equation 18. Computation of expected number of crashes. Step 5. Compute differences in crash estimates between alternatives. As shown in equation 19, the difference between Alternative 1 and 2 yields the number of crashes that installing the work zone QWS is expected to prevent: Expected Crash Difference 54.74 30.65 24.09 crashesALT 1 ALT 2 = − =− Equation 19. Differences in crash estimates between alternatives. The use of an EQWS at this location was computed to result in 24.08 fewer crashes. If, for example, the DOT had found crash severities at previous work zones to be distributed, as Table 13.5 shows, the crash cost benefits of the QWS would be computed to be nearly $1,153,050. The crash cost savings estimate in this analysis assumes that the severity of crashes remains the same in either alternative and is equivalent to the overall average crash severity distribution that the DOT had in previous work zones. Some evidence shows that the severity of crashes that occur when a QWS is implemented is also reduced relative to a no­system condition, which would further increase the crash cost savings that might be achieved. 13.6 General Freeway WZCMFs Table 13.3 presents WZCMFs based on NCHRP Report 627 (Ullman et al. 2008) for injury and fatal crashes, for property­damage­only crashes, and for all crash severity types combined. Generally speaking, the CMFs are higher for property­damage­only crashes than for injury Crash Severities 24.08 Crashes Reduced Fatality (K) 0.005 0.1204 $4.509,991 $543,002.92 Disabling injury (A) 0.018 0.43344 $242,999 $105,325.49 Evident injury (B) 0.088 2.11904 $88,875 $188,329.68 Possible injury (C) 0.136 3.27488 $50,512 $165,420.74 Property damage only (PDO) 0.753 18.13224 $8,325 $150,950.90 Total 1 24.08 n.a. $1,153,030 NOTE: aAverage crash costs are derived from the Highway Safety Manual, 1st edition, updated to 2016 dollars. n.a. = not applicable. Proportion of the Proportional Distribution of Crash Severity Level Average Crash Costa Crash Costs Saved in Alternative 2 Table 13.5. Estimated crash cost savings, Alternative 2 example.

Framework for Evaluation of Work Zone Strategies 233 and fatal crashes. Multiplying the appropriate CMF by the SPF provides an estimate of the crash frequencies expected on a given type of roadway for a given work zone condition. These computations yield the expected number of severe and property­damage­only crashes under each of the three work zone conditions. The crash frequencies estimated using the appropriate SPF and WZCMF can then be multi­ plied by a per crash cost value to assess exposure under each work zone condition as a function of roadway AADT. As noted, work zone–specific CMFs often lack many features of interest. All that can be done is to apply CMFs developed for permanent roadway features (Section 13.7) to what is expected, understanding that the results obtained are only a rough approximation of how an alternative may affect crashes during the time that the work zone is in place. These approximations may provide useful insights into the potential value of the different alternatives being considered; agencies are asked to use engineering judgment in applying the data. 13.7 Available CMFs Table 13.4 presents the available CMFs extracted from NCHRP Research Report 869 (Ullman et al. 2018). More detailed information on these and other non–work zone CMFs can be found in the report. 13.8 Measurable Goals and Performance Measures A successful performance­monitoring and evaluation work zone program generally com­ prises six steps: • Set goals and objectives that are consistent with DOT work zone priorities. • Identify appropriate performance measures to accurately evaluate and monitor goals and objectives. • Identify required data and sources to support calculation of performance measures. • Define appropriate evaluation methods within the constraints of data availability and staff. • Define an appropriate schedule for ongoing, periodic monitoring of the work zone. • Report results in a usable and easily understood format. Successful performance­monitoring and evaluation activities ensure that the project is designed and constructed efficiently. In any assessment of what strategies to include and design into the work zone, agencies need to think through safety considerations along with mobility and other considerations. It takes only one serious crash that can be attributed to the work zone to halt all operations and for the DOT to launch a comprehensive review of all work zone procedures and other activities. The performance measures in Table 13.6 are more specific to evaluation of work zone strate­ gies. Having cursory knowledge of typical performance measures currently in use and those emerging as consistent practice among local, state, and federal transportation agencies helps ensure consistency in work zone performance­monitoring and evaluation practices. Each goal area is discussed in the following subsections. Because the various TMP strategies mitigate effects differently, different approaches are needed for evaluating them. It is generally easier to evaluate capacity­enhancing influences and changes that reduce activity duration than it is to evaluate strategies that influence trip­ making behaviors. This is because a relationship exists between changes in motorists’ trip­ making decisions and behaviors that occur because operating conditions change when a

234 Strategies for Work Zone Transportation Management Plans work zone is introduced. Therefore, agencies might not measure strategies that attempt to affect trip­making decisions and behaviors against what was happening before the work zone implementation, but instead measure relative to what would have occurred had the particular strategy not been implemented. Work zone practitioners may identify one or more metrics that can be measured and that are known or expected to correlate to work zone impacts of concern (i.e., safety, mobility, customer satisfaction, and construction productivity and efficiency), and perform analyses to determine whether the implementation of a strategy affects that metric. 13.8.1 Safety The purpose of a safety evaluation and related MOEs is to assess the effects of a given work zone strategy on the project network safety. Safety is expressed quantitatively through MOEs such as the number of crashes, crash rate, and crash severity. The total number of crashes is an important consideration because of the potential for diversion of traffic with any lane or road closures. The crash rate is an important MOE as it normalizes the number of crashes based on exposure (i.e., the amount of travel on a section of roadway or through an intersection). The crash rate is normally expressed in number of crashes per one million VMT on a section of roadway or in number of crashes per one million vehicles traveling through an intersection. Crash severity is an important consideration because it deals with the cost of crashes in terms of fatalities, injuries, and property damage. Changes in roadway geometry or operations can affect the types of crashes that occur. It is possible to observe an increase in the number of crashes Goal Area Performance Measure Safety Reduction in overall crash rate Reduction in rate of crashes resulting in fatalities and serious injuries Improvement in surrogate measures (i.e., speeding and reckless driving citations) Mobility Reduction in average speed or percentage above PSL Reduction in 85th percentile of percentage above Reduction in travel time Reduction in percent time above predetermined speed Reduction in queue length and duration per time period Increase in throughput (vph) Reduction in change in volume/capacity ratio Environmental Impact Reduction in emissions such as hydrocarbons (HCs), carbon monoxide (CO), carbon dioxide (CO2), and nitrogen oxide (NOx) Customer Satisfaction Change in work zone quality ratings Reduction in the ratings of condition of travel through the work zone Complaint frequency Productivity Reduction in incident or severity rate Reduction in average duration between road repairs Reduction in user cost NOTE: PSL = posted speed limit; vph = vehicles per hour. Table 13.6. Recommended performance measures.

Framework for Evaluation of Work Zone Strategies 235 or the crash rate along a particular section of roadway, but the types of crashes occurring might be less severe. With respect to safety surrogate measures, these are highly site specific and best suited to evaluating strategies when a without­with comparison at each site can be made. For example, the presence of paid law enforcement can be assessed at each project by comparing speeds and erratic maneuvers during times when enforcement is not present to times when it is. Estimating the safety effects of any work zone strategy is difficult because many factors can contribute to the causes and prevention of a crash. These factors include driver skill, driver aggressiveness, driver attention, driver fatigue, speed and speed differential between lanes, level of congestion, type and difficulty of driving maneuver (e.g., changing lanes, making a permissive left turn), lighting, weather, level of law enforcement presence, and roadway geometry and operations. A given strategy might affect one or more of these factors, while other measures being taken (e.g., increase in law enforcement presence) might affect some of these factors as well. In estimating the safety effects, the work zone engineer must consider and control all other potential explanatory factors involved in a crash. 13.8.2 Mobility The purpose of any mobility goal is to estimate the effects of a work zone strategy on project network efficiency. Mobility is expressed quantitatively through MOEs such as travel time delay and travel time variability. Day­to­day variability in overall travel time from a particular origin to a destination is undesirable in a transportation network. Reduction of travel time variability improves the ability of individual citizens and the freight industry to plan and schedule their tasks. Efficiency is expressed by MOEs such as throughput or effective capacity. Effective capacity is the maximum potential rate at which persons or vehicles may traverse a link, node, or network under a representative composite of roadway conditions. Capacity (as defined by the Highway Capacity Manual) is “the maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a given point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic and control conditions.” The HCM defines the major difference between effective capacity and capacity; capacity is assumed to be measured under good weather and pavement conditions and without incidents, whereas effective capacity can vary depending on the work zone strategy or strategies deployed. Throughput is defined as the number of persons, vehicles, or units of freight actually travers­ ing a roadway section or network per unit time. Under certain conditions, measured throughput may reflect the maximum number of vehicles that can be processed by a transportation system. Capacity (and effective capacity) is calculated given the design and operation of the network segment and does not change unless the physical construction or operations of that network segment are changed. In contrast, throughput is an observable measure and, thus, is an MOE for the efficiency of the work zone. Care must be given to interpreting results, however, because throughput changes may be the result of factors besides effective capacity changes (e.g., changes in demand). Thus, not all throughput changes indicate improvements (or lack thereof) in the efficiency of a given situation. These measures can then be further subdivided to reflect certain subsets of time (e.g., peak periods, when lane closures are present) or different dimensions (e.g., duration of queue pres­ ence or average or maximum queue length, average delay per vehicle or total vehicle hours of delay per day). For some strategies, detailed project activity data would be needed to focus the

236 Strategies for Work Zone Transportation Management Plans assessment on the conditions that the strategy attempts to target. Examples of data would be the dates of implementation of night or weekend work or the dates of a major phase change when a particular ramp was closed to traffic. 13.8.3 Environmental Impact The purpose of an emissions assessment is to estimate the effects of the work zone strategy on vehicle emissions. From a systemwide perspective, fuel consumption is important because of its potential effect on the emissions of various gases, including hydrocarbons (HC), carbon monoxide (CO), CO2, and nitrogen oxide (NOx). The primary measure of an emission is its concentration in the atmosphere, usually expressed as grams per cubic centimeter (g/cm3). In addition, the total volume (expressed in tons) of an emission type present in the atmosphere is a useful MOE. For light duty vehicles, the highest emission rates of HC, CO, and NOx generally occurred during the transitional period when traffic changed from free­flow to congested conditions and vice versa; the lowest rates occurred during low­speed work zone congestion periods. However, the highest fuel consumption rates and the highest CO2 emissions occurred under work zone congestion, while the lowest fuel consumption and CO2 emissions occurred with peak hour congestion. Results for heavy duty vehicles were different in that work zone congestion was associated with the highest emissions of HC, CO, and CO2 and the highest fuel consumption, while NOx emission rates under the different traffic conditions were similar. For the freeway scenarios, fuel consumption and greenhouse gas emissions increased by 85 percent and 86 percent, respectively, under heavily congested work zones compared with free­flow conditions without congested work zones. For the multilane (four­ or six­lane) road scenarios, fuel consumption and greenhouse gas emissions increased by 83 percent and 84 percent, respectively, under heavily congested work zones, compared with uncongested traffic conditions. Mitigating congested work zones from heavy (average speeds of 5 mph) to medium congestion (average speeds of 25 mph for a freeway and 15 mph for a multilane road) would reduce fuel consumption and greenhouse gas emissions by 40 percent on a freeway and 32 percent on a multilane road (Zhang, Batterman, and Dion 2011). 13.8.4 Customer Satisfaction One of the key goals of a TMP strategy is to satisfy motorists’ desire for a good driving experience. To improve customer satisfaction, agencies rely heavily on public complaints as an information source for work zone problems that need attention. Some agencies are conducting or commissioning customer surveys to gain feedback regarding work zone safety and mobility performance. These surveys can help agencies plan projects, adjust construction and traffic management strategies, and improve success on future projects. By establishing simple methods of contact, the agencies can enable customer feedback through a project website or another method through which customers’ concerns can be reviewed and addressed. Properly designed survey instruments can help agencies assess the overall effectiveness of TMP strategies and differentiate between individual strategies within a set. Good two­way communication with the public can lessen congestion, since road users can make more informed choices as they plan trips. In addition, keeping the public informed can improve safety if drivers are more aware of prevailing road conditions (Hallmark, Turner, and Albrecht 2013). On the part of a roadway agency, communicating work­zone performance to the public can inspire confidence in the system and show good stewardship. For design and construction teams, communication can lead to improved design specifications and field training.

Framework for Evaluation of Work Zone Strategies 237 13.8.5 Productivity The productivity of work zone construction operations has definitions that range from how effective and safe workers are on the job to exact metrics of how many units of a construction product are accomplished in a certain span of time. The most widely accepted definition focuses on units produced over a defined time duration, or, conversely, on the labor hours needed to produce a unit. The purpose of productivity assessment is to estimate the effects of the work zone strategy on the efficiency of production. Performing the work safely and efficiently, such as implementing the full closure of a roadway, reduces the potential for crashes in a work zone, especially crashes involving both vehicles and workers. Completely closing the roadway to traffic can reduce the duration of the construction, since the contractor does not need to interact with traffic and will likely have access to a larger work space. Both avoiding interaction with the traffic and having access to larger work space will very likely increase the productivity of the contractor and reduce the duration of construction. Other strategies such as night work, extended hours in the off­peak direction of traffic, and multiple lane closures can also improve productivity. The measures pertaining to work productivity are expected to be the most applicable for evaluation of the TMP strategies implemented to reduce the frequency of traffic­affecting events and the total duration of work zone features that affect safety. In general, contractors will benefit from reduced injury costs, reduced construction costs, and, possibly, faster project completion. Road users will also benefit through less traffic congestion and shorter project construction time. 13.8.6 Partnering and Leadership Evaluation Although an important measure, client/contractor satisfaction (i.e., the DOT/contractor) is not discussed in this paper. This measure reflects the clients’ experiences with and confidence in the contractors’ abilities and cooperation. Client satisfaction does not guarantee loyalty (future work with that customer) but generally builds a level of trust and a partnership that can only work positively for the project. A dissatisfied client will tend to review all contractor submissions in detail, partner less, and not work with the contractor in the future. Conversely, a satisfied client still cannot necessarily guarantee future projects to any contractor. Therefore, the main benefit of high client satisfaction for a contractor is the opportunity to remain a client’s potential partner in the future. Client satisfaction measures are generally obtained through periodic partnership workshops and resulting surveys of project staff, both the contractor and client. This activity is carried out by a third party hired by the contractor. Items for evaluation are generally safety, quality, schedule, environmental compliance, issue resolution, responsiveness, communication, and command climate. Each area is evaluated quarterly if both the client and the contractor agree that the executive leadership and partnering is going well. If, however, any one party believes that a breakdown in communication is leading to project­related issues, then these evaluations can be held monthly. An example survey output is shown in Figure 13.3. 13.8.7 Use of Data and Results When agencies measure performance, they may end up with large amounts of data and results. The challenge is to use these results to make good decisions or to take timely and effective action. Project­level results may require immediate action by the responsible party (for example, a maximum queue length in the work zone is exceeded or a high frequency of crashes indicates a traffic control plan may not be working well).

238 Strategies for Work Zone Transportation Management Plans Audiences for data and results can vary from project­level personnel, to district­level manage­ ment, to central­office management, to elected or appointed officials, to the traveling public. These different audiences will be interested in different levels of information. For example, project­level personnel will need detailed results for each performance measure with potential solutions to mitigate negative impacts, whereas upper­level management may only require a quick briefing (if positive) on how things are going. The project contract documents need to carefully outline a scope—what data are to be collected and what expectations or goals the contractor is expected to meet—but allow the contractor to develop the approach (i.e., the public information plan). It is also important to be fair by recognizing and examining the successes as well as the problems and failures. Failure does not have to be recognized by the DOT as non­ compliance, but rather as an opportunity to work with the contractor to mitigate potential issues. Performance data and results will provide a valuable baseline for impact assessment and future project planning. 13.9 Resources and References Hallmark, S., J. Turner, and C. Albrecht. Synthesis of Work-Zone Performance Measures, Smart Work Zone Deployment Initiative and Iowa Department of Transportation, September 2013. Herbel, S., L. Laing, and C. McGovern. Highway Safety Improvement Program (HSIP) Manual, FHWA­SA­09­029, FHWA, U.S. DOT, January 2010. Highway Capacity Manual: A Guide for Multimodal Mobility Analysis, 6th ed. Transportation Research Board, Washington, D.C., 2016. Highway Safety Manual. AASHTO, Washington, D.C., 2010. [HSM] Khattak, A. J., A. J. Khattak, and F. M. Council. Effects of Work Zone Presence on Injury and Non­Injury Crashes, Accident Analysis and Prevention, Vol. 34, 2002. 3.55 2.45 2.45 3.00 3.18 3.09 2.91 2.91 4.35 3.50 3.40 4.30 3.40 3.70 3.85 3.70 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 1. 0 Sa fe ty R ati ng 2. 0 Q ua lit y Ra ti ng 3. 0 Sc he du le R ati ng 4. 0 En vi ro nm en ta l A w ar en es s & Co m pl ia nc e Ra ti ng 5. 0 Is su e Re so lu ti on R ati ng 6. 0 Re sp on si ve ne ss R ati ng 7. 0 Co m m un ic ati on R ati ng 8. 0 Co m m an d Cl im at e / Le ad er sh ip Ra ti ng Ra ti ng (M ax = 5 ) Owner Contractor Figure 13.3. A typical client/contractor monthly evaluation result.

Framework for Evaluation of Work Zone Strategies 239 Ullman, G. L., M. D. Finley, J. E. Bryden, R. Srinivasan, and F. M. Council. NCHRP Report 627: Traffic Safety Evaluation of Nighttime and Daytime Work Zones. Transportation Research Board of the National Academies, Washington, D.C., 2008. Ullman, G. L., M. Pratt, M. D. Fontaine, R. J. Porter, and J. Medina. NCHRP Research Report 869: Estimating the Safety Effects of Work Zone Characteristics and Countermeasures—A Guidebook. Transportation Research Board, Washington, D.C., 2018. http://dx.doi.org/10.17226/25007. Ullman, G. L., M. Pratt, S. Geedipally, B. Dadashova, R. J. Porter, J. Medina, and M. D. Fontaine. NCHRP Web-Only Document 240: Analysis of Work Zone Crash Characteristics and Countermeasures. Transportation Research Board, Washington, D.C., 2018. https://doi.org/10.17226/25006. Zhang, K., S. Batterman, and F. Dion. Vehicle Emissions in Congestion: Comparison of Work Zone, Rush Hour and Free­Flow Conditions. Atmospheric Environment 45 (2011) 1929–1939. National Science Foundation Materials Use: Science, Engineering, and Society Biocomplexity Program Grant and the University of Michigan Risk Science Center, January 2011.

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One of the ways a state department of transportation or other transportation agency can address work zone safety and other impacts is to develop and implement a transportation management plan (TMP).

The TRB National Cooperative Highway Research Program's NCHRP Research Report 945: Strategies for Work Zone Transportation Management Plans provides a practitioner-ready guidebook on how to select and implement strategies that improve safety and traffic operations in roadway construction work zones.

Supplemental materials to the report include NCHRP Web-Only Document 276: Evaluating Strategies for Work Zone Transportation Management Plans; fact sheets on ramp meters, reversible lanes, and truck restrictions; and guidebook appendices.

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