Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook (2018)

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21 Overview This chapter describes CMFs available in existing research that may be applicable to work zone safety analyses. The CMFs were first evaluated with respect to their potential reliabil- ity for work zone safety analyses. The overall reliability of each CMF for work zone analyses was determined using a combination of the applicability and quality ratings for each CMF. For example, highly reliable CMFs were developed using work zone data, and they had good study designs with low standard errors. Unreliable CMFs either had a low quality score or there was reason to doubt their applicability to a work zone. Reliability was categorized as follows: Highly Reliable—The CMF was developed with work zone data and had a high quality score (is included in HSM or has a 4- or 5-star rating from the Clearinghouse). Possibly Reliable—CMFs must meet one of two conditions: 1. The CMF was developed from work zone data with a medium quality score, or 2. The CMF was not developed with work zone data, but there is no obvious reason why it could not be applied to a work zone condition. CMFs developed from non-work-zone data should have a quality score of medium or higher. Unreliable—CMFs meet one of two conditions: 1. CMF has a low quality score, regardless of data source, or 2. CMF was developed using non-work-zone data, but there is reason to doubt its applicability to a work zone. This category applies regardless of quality rating. Treatments and factors with no CMF available are discussed in the final section of this chapter. In those cases, available safety research is reviewed, but no quantitative crash reduction effects are provided. Once the reliability of the available CMFs was established, they were aggregated and cataloged. Tables 4, 5, and 6 summarize the work zone CMFs included in this guidebook, organized by reliability rating. A summary of each treatment or factor is then presented using the elements described below. Description: The treatment for the CMF being computed is briefly described. Applicability to Work Zones: The CMF’s level of applicability to work zones is defined using three categories: Directly Applicable—The CMF was developed using work zone data. Possibly Applicable—The CMF was not developed using work zone data but may be appro- priate for work zone applications. In this case, the base condition, study design, and limitations C H A P T E R 4 Catalog of Available Work Zone CMFs

22 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Feature Applicability toWork Zones Quality Facility Type Table Number Work zone with no lane closure Directly applicable High Freeways and expressways Table 7 Work zone with one or more lanes closed (workers present) Directly applicable High Freeways and expressways Table 8 Work at night (workers present) Directly applicable Medium-High Freeways and expressways Table 9 Directly applicable High Urban Interstate Table 10Increase duration of work zoneIncrease length of work zone Table 11 Table 4. Highly reliable work zone CMFs. Feature Applicability to Work Zones Quality Facility Type Table Number Use stationary enforcement Directly applicable Medium Not specified Table 12 Use automated speed enforcement Possible High Rural two-lane highways Table 13 Use speed feedback display Possible High Not specified Table 14 Use transverse rumble strips Directly applicable, Questionable High Rural freeways, urban/suburban local roads Table 15 Use queue warning system Directly applicable Medium Rural freeways Table 16 Increase inside or outside shoulder width by 1 ft Directly applicable Medium Freeways Table 17 Table 18 Change median width Possible High Stop-controlled intersections, urban and rural freeways Table 19 Change roadside side slope Possible High Rural two-lane and multilane highways Table 21 Change horizontal curve radius Possible Low- Medium Rural two-lane and multilane highways Table 23 Change superelevation variance Possible High Rural two-lane highways Table 24 Remove left turn lane Possible High Rural and urban intersections Table 25 Table 26 Remove right turn lane Possible High Rural and urban intersections Table 27 Table 28 Remove crosswalk Possible Medium Four-leg stop- controlled intersections Table 29 Remove bicycle lane Possible Medium Urban multilane roadways and intersections Table 30 Remove two-way left-turn lane (TWLTL) Possible High Rural two-lane highways and urban intersections Table 31 Reduce lane width Possible High Freeways, rural two- lane and multilane highways Table 33 Table 32 Table 34 Table 35 Reduce shoulder width Possible High Freeway, rural two- lane and multilane highways Table 36 Table 37 Table 38 Table 39 Change vertical alignment (grade and curve) Possible Low- High Rural two-lane highways Table 40 Table 5. Possibly reliable work zone CMFs.

Catalog of Available Work Zone CMFs 23 should be checked before using these CMFs. There are no obvious reasons why these CMFs could not be applied in work zones; however, it is possible that some factors present in the work zone may not have been taken into account. Questionable—A CMF was available for a particular treatment, but there are reasons to believe that the CMF was developed for conditions that may not be directly transferable to a work zone environment. As a result, these CMFs should be used with caution, and limitations should be clearly noted by the analyst. Quality: The quality of a CMF depends on the standard error, number of samples, and study design, irrespective of its applicability to work zones. Hence, a directly applicable CMF can be of low quality and vice versa. The CMFs included in the HSM are considered as high qual- ity CMFs because they underwent extensive review prior to inclusion in the HSM. The CMF Clearinghouse (http://cmfclearinghouse.org) also rates the quality of CMFs. The Clearinghouse rates each CMF with a star rating format. The star quality rating indicates the quality or confidence in the results of the study producing the CMF. The star rating is based on a scale of 1 through 5, with a 5-star rating indicating the most reliable CMFs. Reviewers considered five aspects of each study—study design, sample size, standard error, potential bias, and data source—and judged each CMF according to its performance in each category. More details on the rating system used by the Clearinghouse can be found on its website. For this guidebook, CMFs with 4 or 5 stars were considered to be of high quality, 3 stars were considered to be of medium quality, and 1 or 2 stars were considered to be of low quality. The quality of those CMFs that have not been evaluated by the Clearinghouse was designated as not available (N/A). Facility Type: The type of road to which the CMF is applied. Application to facility types not listed may or may not be appropriate. Work Zone with No Lane Closure Description This CMF applies to a work zone where no lane closure is active. It is considered to be highly reliable. CMFs for conditions when workers are present, and conditions when the presence of workers is unknown, are shown. To develop the worker-present CMFs, daily project inspector Feature Applicability toWork Zones Quality Facility Type Table Number Use work zone variable speed limit Possible High Urban freeway Table 41 Reduce acceleration/deceleration lane length Questionable High Rural and urban freeways Table 42 Reduce intersection sight distance Possible Medium Intersection Table 43 Use crossover work zone Directly applicable Medium Rural multilane Table 44 Use Safety Edge on temporary roadways Possible High Rural two-lane and multilane Table 45 Increase retroreflectivity of markings (above agency standards) Possible Low- Medium Rural two-lane and multilane Table 46 Use left hand merge and downstream shift (Iowa Weave) Directly applicable Low Rural freeway Table 47 Reduce speed limit Questionable Medium- High Principal arterial freeways and expressways Table 48 Install median barrier Questionable High Freeways Table 49Table 50 Table 6. Potentially unreliable work zone CMFs.

24 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook diaries from 64 freeway construction projects in four states (California, North Carolina, Ohio, and Washington) were analyzed (7). This CMF was calculated based on the sites where work activity was occurring somewhere within the project but temporary lane closures were not in place. In a more recent effort involving projects from Ohio, Texas, Virginia, Utah, and Washington, a negative binomial regression model of crashes before and during work zones on Interstates and freeways was used to generate a planning-level work zone CMF that varies as a function of AADT (5). CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: No work zone. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Daytime (workers present) All Freeways and expressways All 1.31 0.03 (7 ) Daytime (workers present) Injury* Freeways and expressways All 1.17 0.04 (7 ) Overall (worker presence unknown) All Four-lane freeways and expressways 5,000– 70,000 AADT NA (5 ) Overall (worker presence unknown) All Six-lane freeways and expressways 50,000– 150,000 AADT NA (5 ) *Injury category includes both serious and minor injuries. NA = not applicable Table 7. Work zone with no lane closure. CMF Application Notes 1. The studies listed in Table 7 did not consider the effect of traffic diversion as the result of the presence of a work zone, so the CMFs only apply to the route that was under construction. 2. The Ullman et al. 2008 study did not control for other changes in roadway cross section, such as lane or shoulder width, so it is possible that these results also include some impact from changes in other characteristics (7). 3. Since the CMF for the Ullman et al. 2008 study was calculated for periods when workers were present, it may overestimate crashes if applied to all periods when the work zone is in place (7). It is possible that the presence of workers may induce rubbernecking and additional distractions that would increase crashes relative to times when the work zone is in place but no construction or maintenance activities are under way. 4. The CMFs for the Ullman et al. 2018 study may have experienced occasional short-term or short-duration lane closures (5). No attempt was made to quantify the frequency of these lane closures in the analysis.

Catalog of Available Work Zone CMFs 25 Work Zone with One or More Lanes Closed (Workers Present) Description This CMF applies to work zones where at least one travel lane is closed and workers are pres- ent. The CMFs developed did not distinguish between the number of base lanes and the number of lanes closed at a site, so it may not fully account for specific geometric effects. To develop these CMFs, daily project inspector diaries from 64 freeway construction projects in four states (California, North Carolina, Ohio, Washington) were analyzed to determine hours of work, hours and locations of temporary lane closures, and number of travel lanes closed during each work period (7). CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: No work zone. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Daytime All Freeways and expressways All 1.66 0.07 (7 ) Daytime Injury* Freeways and expressways All 1.46 0.11 (7 ) *Injury category includes both serious and minor injuries. Table 8. Work zone with one or more lanes closed (workers present). CMF Application Notes 1. The information presented in Table 8 is from an evaluation that did not examine the differ- ence in safety effects between the closure of a single lane and the closure of multiple lanes. Also, initial lane configuration of the roadway was not considered. 2. This study did not consider the effect of traffic diversion as the result of the presence of a work zone, so the CMF only applies to the route that was under construction. 3. Since the CMF was calculated for periods when workers were present, it may overestimate crashes if applied to all periods when the work zone is in place. The presence of workers may induce rubbernecking and additional distractions that would increase crashes relative to times when the work zone is in place but no construction or maintenance activities are underway. 4. There were 64 project sites used to develop these CMFs. The majority of projects where tem- porary lane closures were performed during the day occurred at locations where AADTs were relatively low, and at night at locations where AADTs were relatively high. Work at Night (Workers Present) Description Performing work at night reduces operational impacts on traffic because volumes are lower; however, lower light levels at night may reduce visibility for drivers and construction workers and introduce glare issues. These factors can affect construction zone crash risk and crash severity.

26 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Separate CMFs were developed for sites with lane closures and sites without lane closures. Again, the CMFs for night work at lane closures did not differentiate between the base number of lanes and the number of lanes closed. CMFs were also developed for periods when workers were present, so these may overestimate crashes if applied to periods when work was not under way. CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: No work zone present. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Work zone with one or more lanes closed (workers present) Nighttime All Freeways and expressways All 1.61 0.06 (7 ) Nighttime Injury* Freeways and expressways All 1.42 0.09 (7 ) Work zone with no lane closure (workers present) Nighttime All Freeways and expressways All 1.58 0.15 (7 ) Nighttime Injury* Freeways and expressways All 1.41 0.23 (7 ) *Injury category includes both serious and minor injuries. Table 9. Work at night (workers present). CMF Application Notes 1. For the information presented in Table 9, nighttime crashes were defined as those occurring from 7:00 p.m. to 6:00 a.m. 2. This evaluation did not examine the difference in safety effects between the closure of a single lane and the closure of multiple lanes. Also, initial lane configuration of the roadway was not considered. 3. Nighttime work zones with no lane closure were a fairly infrequent event. Consequently, the CMFs had a large standard error associated with the estimates, and should be used with caution. 4. Because the CMFs were calculated for periods when workers were present, they may over- estimate crashes if applied to all periods when the work zone is in place. It is possible that the presence of workers may induce rubbernecking and additional distractions that would increase crashes relative to times when the work zone is in place but no construction or main- tenance activities are under way. Increase Work Zone Duration or Length Description The HSM documents the result of a study that examined how changing the duration or length of a work zone would impact expected crashes (8). The CMFs developed were created relative to a base case of a work zone with a duration of 16 days and a length of 0.51 miles.

Catalog of Available Work Zone CMFs 27 CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. CMFs are applicable to work zones with durations of between 16 and 714 days and lengths between 0.5 and 12.2 miles. Base Condition: Work zone with a duration of 16 days and a work zone length of 0.51 miles. Note that the percent increases in the CMF formulas in Table 10 and Table 11 are calculated relative to these base conditions (e.g., a work zone with a length of 1.02 miles would be a 100% increase in length over the 0.51-mile base condition). Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Freeway 4,000 to 237,000 AADT 0.959 (8 ) Table 10. Increase duration of work zone. Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Freeway 4,000 to 237,000 AADT 0.530 (8 ) Table 11. Increase length of work zone. CMF Application Notes 1. CMFs in Tables 10 and 11 were developed using a negative binomial regression cross-sectional study design using work zone data from California. 2. The study design did not isolate other changes in roadway cross section, so these CMFs may also include effects related to other work zone design elements. 3. Please see notes under base condition to ensure that formulae are applied correctly. Use Stationary Police Enforcement Description Stationary police enforcement involves an officer in a patrol car being deployed adjacent to the travel lanes within or upstream of a work zone. Two main types of stationary police enforce- ment can be used. If the emphasis is on active identification and citation of traffic law violators, the enforcement officer may choose either an overt strategy (positioning a marked vehicle in full view of approaching traffic) or a covert strategy (using an unmarked vehicle or positioning his or her vehicle out of view of oncoming traffic) (9). On the other hand, if the goal is to alert approaching drivers and calm traffic rather than issue citations, the officer and marked vehicle can be positioned in full view close to the travel lanes with emergency lights flashing. CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: No enforcement used.

28 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Not specified 696 to 124,907AADT .585* Not calculated (10) * Use with caution. Authors stated that the CMF value “…seemed to be quite large and difficult to justify solely from the expected speed reduction caused by police enforcement” (10 ). Table 12. Use stationary police enforcement. CMF Application Notes 1. The CMF in Table 12 was obtained using data from Indiana work zones and a random-effect negative binomial crash frequency model, where each observation represented 1 month of data. Detailed hourly data with enforcement efforts was not available at enough sites to be used in the model. The authors noted that about 90% of the enforcement observations referred to conspicuous and ticketing enforcement (i.e., overt and active). 2. Other studies have shown speed reductions associated with stationary enforcement in the order of 5 to 13 mph for rural freeways, 3 to 8 mph for urban freeways, and 9 mph in a study conducted along an urban arterial (11, 12, 13). Although speed reductions of as much as 13 mph have been recorded with stationary enforcement, 5 to 7 mph reductions are more common, especially on high-volume, high-speed roadways (9). 3. Stationary enforcement will typically result in a greater speed reduction than circulating patrols and automated speed enforcement, but its spatial effects will be more localized. Spatial effects may be found from just before the officer location to approximately 1 mile downstream (14). Therefore, where speed reductions at a spot location are desired, the officer and vehicle should be positioned at a short distance (e.g., 1,000 ft is suggested). In addition, studies suggest that the temporary effect of stationary enforcement may not be significant after the departure of police (12). Use Automated Speed Enforcement Description Automated speed enforcement programs are promising safety countermeasures that have been tried in many countries and in a few states. Photo speed enforcement systems can consis- tently cite more drivers than traditional police enforcement, which can increase compliance with posted speed limits. Another benefit is that they do not require officers to risk injury by exposing themselves to vehicles moving at high speeds through the work zone (15). Previous studies have shown that safety effects from speed enforcement diminish with time as travelers become more aware of the cameras. Also crash reductions seem to be higher in corridors that had a higher density of automated speed enforcement devices (16). Caution should be taken before selecting automatic speed enforcement as a safety countermeasure because it is not always welcomed by the general public or policy makers due to privacy concerns. Likewise, legislation permitting automatic speed enforcement usage must be present, which is not the case in many jurisdictions. CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: No automated enforcement demonstration program.

Catalog of Available Work Zone CMFs 29 Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All Fatal, injury* All Not specified 0.83 0.01 (unadjusted) (4 ) *Injury category includes both serious and minor injuries. Table 13. Use automated speed enforcement (relative to no enforcement). CMF Application Notes 1. There were no studies available that specifically examined the safety effects of using automated speed enforcement in work zones. The CMF listed in Table 13 was derived from past studies on non-work-zone roads. Use Speed Feedback Displays Description Speed feedback displays consist of a digital display that shows the speed of approaching traffic. Figure 9 shows an example of a speed feedback display. Speeds are typically detected using radar, and the posted speed limit is often shown somewhere on the display so that drivers can determine if they are exceeding the posted speed limit. Speed feedback displays may be either (a) portable, trailer-mounted units or (b) permanent installations. In work zones, typical appli- cations are trailer-mounted units placed in the advance warning area. Past studies have shown that speed feedback displays can be more effective at reducing speeds within the work zone than static speed limit signs (17, 18, 19). CMFs Applicability to Work Zones: Possibly applicable, although CMFs were not developed with work zone data, so caution should be used for work zone applications. Available CMFs may have been collected under conditions that were not similar to work zones. Base Condition: Absence of speed feedback displays. Figure 9. Trailer-mounted work zone speed feedback display.

30 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Not specified Not specified 0.54 0.2 (4 ) Table 14. Use speed feedback displays. CMF Application Notes 1. While speed feedback displays may be used to manage work zone speeds, there were no studies available that examined safety effects in work zones specifically. The CMF listed in Table 14 was derived from a meta-analysis of past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. Likewise, the types of roads included in the meta-analysis were not specified, so this CMF may be influenced by data collected on lower volume residential streets. These values should be used with caution. Use Transverse Rumble Strips Description Transverse rumble strips can be raised bars or grooves placed perpendicular to the direction of travel. They may be used in work zones to provide advance warning to drivers approaching work zones and to manage speeds. Although rumble strips are sometimes used in work zones (see Figure 10), most prior studies that developed CMFs have focused on traffic calming or intersection applications (as shown in Figure 11) that may not be transferable to a work zone. One evaluation performed as part of this research project focused on portable transverse rumble strips that are put down prior to closing a lane for a single work shift and then picked up when the lane closure is removed. CMFs Applicability to Work Zones: Likely applicable for short-term application to Interstate lane closures. Possibly applicable for long-term applications; however, those CMFs were not Figure 10. Portable transverse rumble strips on Interstate work zone application.

Catalog of Available Work Zone CMFs 31 developed with work zone data. The CMFs were developed using conditions that are likely to vary significantly from a work zone. Base Condition: No transverse rumble strips present. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Install portable transverse rumble strips at short-term nighttime Interstate lane closures Nighttime All Rural Interstate when queues were not present 55,000–110,000 AADT 0.890 (not significant) 0.377 (5 ) Nighttime All Rural Interstate when queues were present 55,000–110,000 AADT 0.397 0.265 (5 ) Install transverse rumble strips on stop-controlled approaches of an intersection All All Rural three- and four-leg stop- controlled intersection Not specified 1.118 0.086(unadjusted) (21) All Fatal, serious injury Rural three- and four-leg stop- controlled intersection Not specified 0.785 0.107 (unadjusted) (21) Install transverse rumble strips on roadway segment as traffic-calming devices All Injury* Urban and suburban local roads Not specified 0.64 0.12 (22) *Injury category includes both serious and minor injuries. Table 15. Use transverse rumble strips. CMF Application Notes 1. The CMFs for the short-term nighttime Interstate lane closures found that the portable transverse rumble strips did not have a significant effect on crashes when traffic queues were not present at the lane closures. However, if traffic queues did form, the rumble strips reduced crashes that were expected to have occurred by 60%. 2. The CMFs listed in Table 15 for intersections and as traffic-calming devices on local roads were derived from past studies on non-work-zone situations, so their potential applicability to Figure 11. Transverse rumble strips for permanent applications (20).

32 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook a work zone situation is unclear. These values should be used with caution. Applications were primarily to alert drivers to stop signs or traffic calming on local roads, so it is unclear if these safety effects could be translated to a work zone. 3. For the long-term intersection application, the CMF for total crashes was not statistically significant, but there was a statistically significant reduction in fatal and serious injury crashes. Use Queue Warning Systems Description Queue warning systems use real-time data to dynamically alert traffic to stopped or slowed traffic downstream. For work zone applications, messages are typically displayed on portable changeable message signs. Large speed differentials between traffic approaching the end of a slow- moving traffic queue formed by a lane closure have sometimes been identified as a significant contributor to work zone rear-end collisions. Countermeasures that can reduce this rear-end collision potential at work zones where queues develop is of high interest to agencies and con- tractors nationally. During the widening effort on Interstate 35 through central Texas, Texas Department of Transportation (TxDOT) officials wanted to examine and implement technologies to help mitigate the impacts of end-of-queue crashes. An end-of-queue warning system was established, consisting of a highly portable work zone ITS of easily deployable radar speed sensors linked to one or more portable changeable message signs (PCMS). The end-of-queue warning system was deployed upstream of nighttime lane closures where queues are expected to develop. The system was deployed in conjunction with portable transverse rumble strips. CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: No queue warning system present. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Nighttime All Rural Interstate where queues were expected 55,000 to 110,000 AADT 0.559 0.255 (6 ) Nighttime All Rural Interstate when queues were actually present 55,000 to 110,000 AADT 0.468 0.301 (5 ) Nighttime All Rural Interstate when queues were not actually present 55,000 to 110,000 AADT 0.717 (not significant) 0.353 (5 ) Table 16. Use queue warning systems. CMF Application Notes 1. The CMFs listed in Table 16 were developed through an empirical Bayes analysis using 234 control and 216 treatment nights of lane closures. The sample sizes were very small in terms of both expected and actual crashes because less than 1 year’s worth of nighttime lane closures from each condition was available for analysis.

Catalog of Available Work Zone CMFs 33 2. For the Ullman et al. 2016 study, queues were assumed to have occurred for some period of time at all nights examined in this study (6). However, this was not verified. Also, the duration of any queues that occurred was not measured. 3. For the Ullman et al. 2018 study, Bluetooth data was used to identify actual periods when queues were present and periods when queues were not present (5). 4. Because all data was collected along a single corridor with multiple work zones, results may or may not be transferable to other locations. 5. In the Ullman et al. 2018 study, the CMFs for the queue warning system plus portable rumble strips were found to be similar to the CMFs for portable rumble strips only (5) (see Table 15). The effect of the queue warning system without the use of portable rumble strips could not be ascertained. Increase Inside or Outside Shoulder Width in Work Zone by 1 Ft Description The safety effect of increasing the inside and outside shoulder width in a work zone was examined using cross-sectional data on I-70 in Indianapolis, Indiana (23). A cross-sectional study design was used because a number of countermeasures were in place, but the researchers were able to estimate the isolated impact of increasing the shoulder width by 1 ft on both the inside and the outside shoulder. While CMF standard errors were low, results are based on a single corridor, so transferability to other sites remains uncertain. CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: Shoulder width prior to work zone installation. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Urban Interstate Not specified 0.97 0.01 (23) Table 17. Increase inside shoulder width by 1 ft. Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Urban Interstate Not specified 0.948 0.01 (23) Single vehicle All Urban Interstate Not specified 1.043 0.02 (23) Table 18. Increase outside shoulder width by 1 ft. CMF Application Notes 1. CMFs listed in Tables 17 and 18 were developed using a regression cross-sectional study design using work zone data. Although standard error values produced were low, the CMF developed was produced from data from a single Interstate route. Transferability of the CMF to other locations remains uncertain.

34 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Change Median Width Description Medians serve to provide physical separation between opposing directions of traffic. Numer- ous studies have reported crash reductions due to the presence of medians (22, 24, 25, 26). The type of crash most affected by the presence of a median or width of median is cross-median crashes. A cross-median crash is defined as a scenario where a vehicle departs its traveled way to the left, traverses the separation between the highway’s directional lanes, and collides with a vehicle traveling in the opposite direction. During construction, there may be a temporary reduction in median width as lanes are shifted to accommodate the work zone. Currently, no CMF is available for decreasing median width; however, the HSM includes CMFs for increasing median width. For work zones, it is assumed that the effect of decreasing median width is the inverse of increasing median width. CMFs Applicability to Work Zones: Possibly applicable. CMFs for increasing median width were not developed with work zone data, so caution should be used for work zone applications. Table 19 provides a few CMFs for increasing the median width, whereas Table 20 presents CMFs for reducing the median width. Base Condition: Base conditions vary depending on whether the CMF is for a segment or intersection. The original base conditions were set for widening medians, so the inverse of those CMFs are presented here. The original base conditions for widening the medians are as follows: • Four-lane highways with full access control: 10-ft-wide traversable median for a four-lane highway with full access control (25) • Stop-controlled intersections: Median wider than 80 ft (maximum median width of 300 ft) (26) Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Multivehicle All Rural four-leg approach Not specified 1.04 0.02 (26)Multivehicle All Urban and suburban four-leg approach Not specified 0.94 0.01 Multivehicle All Urban and suburbanthree-leg approach Not specified 0.98 0.01 Table 19. Increase median width in 3-ft increments (intersections). Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 20 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 1.16 0.02 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.12 0.04 (unadjusted) Table 20. Reduce median width (segments).

Catalog of Available Work Zone CMFs 35 CMF Application Notes 1. The CMF values in Tables 19 and 20 were calculated by finding the inverse of CMF values for providing left turn lanes. The standard error is from the original study (CMF for increasing median width). Caution should be taken before using these values. 2. Segment CMFs are presented here for only fully access-controlled facilities for the sake of brevity. Please refer to the HSM for additional CMFs for divided highways with partial or no access control (4). 3. The CMFs were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 4. Roads with full access control experience relatively fewer cross-median crashes probably because these roads generally have larger median widths. In the sample for this research, the average median width for roads with full access control ranged from 55 to 60 ft, Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 30 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 1.35 0.04 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.25 0.07 (unadjusted) 40 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 1.59 0.05 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.41 0.09 (unadjusted) 50 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 1.85 0.06 (unadjusted) Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.56 0.1 (unadjusted) (25 ) 60 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 2.17 0.07 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.75 0.1 (unadjusted) 70 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 2.5 0.07 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 1.96 0.1 (unadjusted) 80 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 2.94 0.07 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 2.17 0.1 (unadjusted) 90 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 3.45 0.07 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 2.44 0.1 (unadjusted) 100 ft to 10 ft conversion Cross median Not specified Rural freeway 2,400 to 119,000 AADT 4.00 0.06 (unadjusted) (25 )Cross median Not specified Urban freeway 4,400 to 131,000 AADT 2.78 0.1 (unadjusted) Table 20. (Continued).

36 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook whereas the average median width for roads with partial or no access control ranged from 29 to 40 ft. 5. For rural intersections, the confidence interval may contain 1. The HSM recommends using the rural intersection CMF with caution. Change Roadside Side Slope Description The steepness of the roadside slope (or side slope) is a cross-sectional feature that affects the likelihood of an off-road vehicle rolling over or recovering back into the travel lane. As part of their 1987 study, Zegeer et al. developed relationships between single-vehicle crashes and field-measured side slopes from 1:1 to 7:1 or steeper for 1,776 miles of roadway in three states: Alabama, Michigan, and Washington (27). CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Prior condition varied depending on CMF type. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 1V:7H to 1V:2H or steeper All Not specified Rural Not specified 1.18 Not specified (4 ) 1V:7H to 1V:4H All Not specified Rural Not specified 1.12 Not specified (4 ) 1V:7H to 1V:5H All Not specified Rural Not specified 1.09 Not specified (4 ) 1V:7H to 1V:6H All Not specified Rural Not specified 1.05 Not specified (4 ) Table 21. Increase roadside side slope. Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 1V:2H to 1V:4H All Not specified Rural Not specified 0.94 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.9 Not specified (4 ) 1V:2H to 1V:5H All Not specified Rural Not specified 0.91 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.85 Not specified (4 ) 1V:2H to 1V:6H All Not specified Rural Not specified 0.88 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.79 Not specified (4 ) 1V:2H to 1V:7H All Not specified Rural Not specified 0.85 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.73 Not specified 1V:3H to 1V:4H All Not specified Rural Not specified 0.95 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.92 Not specified (4 ) Table 22. Reduce roadside side slope.

Catalog of Available Work Zone CMFs 37 CMF Application Notes 1. The CMFs listed in Tables 21 and 22 were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution. The CMFs may not account for other objects that might be present on the roadside during construction, such as construction equipment or material. 2. Through NCHRP Projects 17-25 and 17-29, an expert panel on rural multilane highways was convened. This panel concluded that the CMFs derived were valid and the best available for both rural two-lane roads and rural multilane highways (25). These CMFs are included in the HSM. Change Horizontal Curve Radius Description Past research has shown that horizontal curves experience crash rates of up to four times the rates on tangent sections, all else being equal (27, 28). A number of researchers have found that milder curves are associated with lower crash rates compared with sharper curves (29, 30). Work zone activities may alter horizontal curvature during construction. CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications, especially in cases where there may be interactions with barriers or other work zone features. Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 1V:3H to 1V:5H All Not specified Rural Not specified 0.92 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.86 Not specified (4 ) 1V:3H to 1V:6H All Not specified Rural Not specified 0.89 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.81 Not specified (4 ) 1V:3H to 1V:7H All Not specified Rural Not specified 0.85 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.74 Not specified (4 ) 1V:4H to 1V:5H All Not specified Rural Not specified 0.97 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.94 Not specified (4 ) 1V:4H to 1V:6H All Not specified Rural Not specified 0.93 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.88 Not specified (4 ) 1V:4H to 1V:7H All Not specified Rural Not specified 0.89 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.81 Not specified (4 ) 1V:5H to 1V:6H All Not specified Rural Not specified 0.97 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.94 Not specified (4 ) 1V:5H to 1V:7H All Not specified Rural Not specified 0.92 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.86 Not specified (4 ) 1V:6H to 1V:7H All Not specified Rural Not specified 0.95 Not specified (4 ) Single vehicle Not specified Rural Not specified 0.92 Not specified (4 ) Table 22. (Continued).

38 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Base Condition: For the first CMF, the base condition is a tangent section. For rural four-lane highways, the base condition is roadways with a maximum speed limit of 55 mph (31). Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Modify horizontal curve radius and length and provide spiral transitions All Rural two-lane minor arterial Not specified = Length of curve including length of spiral (if present) (mi) R = Radius of curvature (ft) S = 1 if spiral transition is present, otherwise 0 Not specified (4 ) Increase in horizontal curvature from X to Y degrees All Fatal and injury* Rural four-lane highways Not specified Not specified (31) *Injury category includes both serious and minor injuries. All Table 23. Change horizontal curve radius. CMF Application Notes 1. The CMFs listed in Table 23 were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 2. Fitzpatrick et al. (2009) used datasets from Texas freeways that included 561 curve/tangent pairs for a total of 324.3 miles and 1,122 segments (31). When separate models were estimated for each area type/number of lane category, the result was significant for the rural, four-lane freeways at the 5% significance level, was significant for the urban, four-lane freeways at the 10% level, and was not significant for urban, six- or eight-or-more-lane freeways. 3. In addition to the freeway CMF listed, the HSM 2014 Supplement includes CMFs for horizontal curvature broken down by single/multiple vehicle crashes and PDO/fatal-injury crashes (32). They are not presented here for the sake of brevity but can be found in Chapter 18 of the HSM Supplement. Change Superelevation Variance Description The CMF for superelevation is based on the superelevation deficiency of a horizontal curve (i.e., the difference between the actual superelevation and the superelevation required by AASHTO policy). When the actual superelevation meets or exceeds that required by AASHTO policy, the value of the superelevation CMF is 1.00. An expert panel made a judgment that there would be no effect of superelevation deficiency on safety until the superelevation deficiency exceeds 0.01. CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Based on a horizontal curve radius of 842.5 ft.

Catalog of Available Work Zone CMFs 39 Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source 0.01 ≤ SV ≤ 0.02 All All Rural two-lane arterial Not specified 1+6*(SV–0.01) Not specified (33 ) SV > 0.02 All All Rural two-lane arterial Not specified 1+3*(SV–0.02) Not specified (33 ) Table 24. Change superelevation variance (SV). CMF Application Notes 1. The CMFs in Table 24 are included in the HSM. However, they were derived from non- work-zone data, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 2. These CMFs were developed based on a horizontal curve radius of 842.5 ft. To determine the CMF for changing that condition, the “new” condition CMF should be divided by the “existing” condition CMF. Remove Left Turn Lane Description Removing turn lanes from an intersection affects the safety and capacity of that facility. Cur- rently, no CMF is available for removing left turn lanes; however, the HSM includes a CMF for providing left turn lanes. For work zones, it is assumed that the effect of removing left turn lanes is the inverse of providing left turn lanes. CMFs Applicability to Work Zones: Possibly applicable. CMFs for adding left turn lanes were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Intersection where the left turn lane has been temporarily closed by a work zone. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Rural, three-leg stop-controlled intersection 1,600 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 1.79 0.07 (4 ) All All Rural, three-leg stop-controlled intersection 1,600 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 1.39 0.03 (4 ) All All Urban, four-leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 200 to 8,000 (minor road AADT) 1.37 0.04 (4 ) All All Urban, four-leg signalized intersection 4,600 to 40,300 (major road AADT) 100 to 13,700 (minor road AADT) 1.32 0.03 (4 ) Table 25. Remove left turn lanes from one major approach. (continued on next page)

40 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Urban, four-leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 2,600 (minor road AADT) 1.11 0.1 (4 ) All Fatal, injury* Rural, three-leg stop-controlled intersection 1,600 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 2.22 0.1 (4 ) All Fatal, injury* Rural, four-leg stop-controlled intersection 1,600 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 1.54 0.04 (4 ) All Fatal, injury* Urban, four-leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 200 to 8,000 (minor road AADT) 1.41 0.05 (4 ) All Fatal, injury* Urban, four-leg signalized intersection intersection 4,600 to 40,300 (major road AADT) 100 to 13,700 (minor road AADT) 1.39 0.06 (4 ) 7,200 to 55,100 (major road AADT) 550 to 2,600 (minor road AADT)All Fatal, injury* Urban, four-leg signalized 1.10 0.02 (4 ) *Injury category includes both serious and minor injuries. Table 25. (Continued). Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Rural, four-leg stop-controlled intersection intersection 1,500 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 1.92 0.04 (4 ) All All Urban, four-leg stop-controlled 1,500 to 40,600 (major road AADT)200 to 8,000 (minor road AADT) 1.89 0.04 (4 ) All All Urban, four-leg signalized intersection 4,600 to 40,300 (major road AADT) 100 to 13,700 (minor road AADT) 1.72 0.04 (4 ) All Fatal,injury* Rural, four-leg stop-controlled intersection 1,500 to 32,400 (major road AADT) 50 to 11,800 (minor road AADT) 2.38 0.04 (4 ) All Fatal,injury* Urban, four-leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 200 to 8,000 (minor road AADT) 2.00 0.06 (4 ) All Fatal, injury* Urban, four-leg signalized intersection 4,600 to 40,300 (major road AADT) 100 to 13,700 (minor road AADT) 1.92 0.07 (4 ) All Fatal,injury* Urban, four-leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 2,600 (minor road AADT) 1.20 0.02 (4 ) *Injury category includes both serious and minor injuries. Table 26. Remove left turn lanes from both major approaches. CMF Application Notes 1. Tables 25 and 26 list the CMF values calculated by finding the inverse of CMF values for providing left turn lanes. The standard error is from the original study (CMF for providing left turn lanes). Caution should be taken before using these values. 2. These CMFs are included in the HSM. However, they were derived from non-work-zone data, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 3. The study was limited to projects at three- and four-leg intersections. The database assembled for the 580 study intersections included a total of 26,056 intersection-related accidents in the District of Columbia, Illinois, Iowa, Louisiana, Minnesota, Montana, Nebraska, New Jersey, North Carolina, Oregon, and Virginia.

Catalog of Available Work Zone CMFs 41 Remove Right Turn Lane Description Removing right turn lanes from an intersection affects the safety and capacity of that facility. Currently, no CMF is available for removing right turn lanes; however, the HSM includes a CMF for providing right turn lanes. For work zones, it is assumed that the effect of removing right turn lanes is the inverse of providing them. CMFs Applicability to Work Zones: Possibly applicable. CMFs for adding right turn lanes were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Intersection where the right turn lane has been temporarily closed by a work zone. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Three-leg and four- leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 25 to 26,000 (minor road AADT) 1.16 0.06 (4 ) All All Three-leg and four- leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 8,400 (minor road AADT) 1.04 0.02 (4 ) All Fatal, injury* Three-leg and four- leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 25 to 26,000 (minor road AADT) 1.30 0.08 (4 ) All Fatal, injury* Three-leg and four- leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 8,400 (minor road AADT) 1.10 0.04 (4 ) *Injury category includes both serious and minor injuries. Table 27. Remove right turn lanes from one major approach. Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Three-leg and four- leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 25 to 26,000 (minor road AADT) 1.35 0.08 (4 ) All All Three-leg and four- leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 8,400 (minor road AADT) 1.09 0.03 (4 ) All Fatal, injury* Three-leg and four- leg stop-controlled intersection 1,500 to 40,600 (major road AADT) 25 to 26,000 (minor road AADT) 1.69 Not specified (4 ) All Fatal, injury* Three-leg and four- leg signalized intersection 7,200 to 55,100 (major road AADT) 550 to 8,400 (minor road AADT) 1.20 Not specified (4 ) *Injury category includes both serious and minor injuries. Table 28. Remove right turn lanes from both major approaches.

42 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook CMF Application Notes 1. The CMF values listed in Tables 27 and 28 were calculated by taking the inverse of the CMF values for providing right turn lanes. The standard error in the table is from the original study (CMF for providing right turn lanes). Caution should be taken before using these values. 2. These CMFs are included in the HSM, but they were derived from non-work-zone data, so their applicability to a work zone situation is unclear. These values should be used with caution. 3. The study was limited to projects at three- and four-leg intersections. The database assembled for the 580 study intersections included a total of 26,056 intersection-related accidents in the District of Columbia, Illinois, Iowa, Louisiana, Minnesota, Montana, Nebraska, New Jersey, North Carolina, Oregon, and Virginia. Remove Crosswalk from Minor Approaches Description Removing crosswalks from an intersection affects the pedestrian safety of that facility. While CMFs do exist for crosswalk installation, they do not exist for removal of a crosswalk. It is assumed that the effect of removing a crosswalk is the inverse of providing a crosswalk at an intersection. CMFs Applicability to Work Zones: Possibly applicable. CMFs are assumed to be the inverse of providing a crosswalk on the minor approach of an intersection. Base Condition: A four-leg stop-controlled intersection where a crosswalk has been removed from the minor approach. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Four-leg stop- controlled intersection Not specified 2.66 Not specified (34 ) Table 29. Remove crosswalk from a minor approach. CMF Application Notes 1. The CMF value listed in Table 29 was calculated by taking the inverse of the CMF values for providing a crosswalk. Caution should be taken before using this value. 2. The analysis conducted by Haleem et al. (2011) was performed on 2,475 unsignalized intersections collected from six counties in Florida (34). Remove Bicycle Lane Description Bicycle lanes enable bicyclists to travel at their preferred speed and facilitate predictable behavior and interactions between bicyclists and motorists. If these lanes are removed as part of a work zone, there could be negative safety consequences. Because no CMFs exist for

Catalog of Available Work Zone CMFs 43 removing bicycle lanes, it is assumed that the effect of removing a bicycle lane is the inverse of providing one. CMFs Applicability to Work Zones: Possibly applicable. CMFs are assumed to be the inverse of providing a bicycle lane facility. CMFs for adding a bicycle lane were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Roadway segments and intersections where a bicycle lane has been removed. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source All All Urban multilane road segment Not specified 1.06 0.101 (unadjusted) (35 ) All Fatal, injury* Urban multilane road segment Not specified 1.06 0.114 (unadjusted) (35 ) All All Urban three-leg and four-leg intersections Not specified 0.95 0.053 (unadjusted) (35 ) All Fatal, injury* Urban three-leg and four-leg intersections Not specified 0.93 0.059 (unadjusted) (35 ) *Injury category includes both serious and minor injuries. Table 30. Remove bicycle lanes. CMF Application Notes 1. The CMF values listed in Table 30 were calculated using the inverse of the CMF values for providing bicycle lanes. The standard error in the table is from the original study (CMF for providing bicycle lane). Caution should be taken before using these values. 2. The data was collected on the intersections and roadway segments of New York City from 1999 to 2008. A before–after study was performed on the data. Remove TWLTL from Major Approach Description A TWLTL can provide lateral separation between opposing traffic, yet allow the full comple- ment of turning movements (e.g., left turns into and out of access points). If these lanes are removed as part of a work zone setup, safety may be affected. No CMFs for removal of TWLTLs were found, so it is assumed that the effect of removing a TWLTL is the inverse of providing it. CMFs Applicability to Work Zones: Possibly applicable. CMFs are assumed to be the inverse of providing TWLTLs. The CMF for adding TWLTLs was not developed with work zone data, so caution should be used for work zone applications. Base Condition: TWLTL removed from a road with a driveway density ≥5 driveways per mile.

44 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Available CMFs Crash Type Crash Severity Facility Type Range Volume Standard CMF Error Source All Rural two-lane arterial Not specified = proportion of driveway-related crashes = TWLTL-involved left turn crashes as a proportion of driveway- related crashes Not calculated (4 ) All All All Urban and rural two-lane road Not specified 1.25 (unadjusted) (36 ) All Fatal, injury* Urban and rural two-lane road Not specified 1.35 0.03 0.07 (unadjusted) (36 ) *Injury category includes both serious and minor injuries. Table 31. Remove TWLTL. CMF Application Notes 1. The CMF values listed in Table 31 were calculated using the inverse of the CMF values for providing a TWLTL. The standard error in the table is from the original study (CMF for providing TWLTL). Caution should be taken before using these values. 2. Geometric, traffic, and crash data were obtained for 78 sites in North Carolina, 10 sites in Illinois, 31 sites in California, and 25 sites in Arkansas. The Empirical Bayes method was used to determine the safety effectiveness of installing the TWLTLs. Reduce Lane Width Description Work zone activities may require that lane widths be reduced to accommodate construction or maintenance activities (see Table 32). The HSM considers a 12-ft-wide lane as the standard, but narrower lane widths are also possible. The HSM provides CMFs for reduced lane widths, but these CMFs do not consider interactions with shoulder widths or barriers that may be present in work zones. As a result, it is unclear if these CMFs can be directly applied because the impact of interactions with other work zone features is not considered. CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed using work zone data and do not consider interactions with work zone features. Base Condition: A 12-ft-wide lane. Available CMFs Crash Type Severity Facility Crash Type Volume Range CMF Error SourceStandard Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane, divided and undivided multilane <400 AADT 1.01 Not calculated (4 ) Table 32. Reduce lane width from 12 ft to 11 ft (non-freeway).

Catalog of Available Work Zone CMFs 45 Crash Type Severity Facility Crash Type Volume Range CMF Error SourceStandard Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway >2,000 AADT 1.05 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway >2,000 AADT 1.04 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway >2,000 AADT 1.03 Not calculated (4 ) Table 32. (Continued). Crash Type Severity Facility Crash Type Volume Range CMF Error SourceStandard Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane, undivided multilane roadway <400 AADT 1.02 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway >2,000 AADT 1.30 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway >2,000 AADT 1.23 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway <400 AADT 1.01 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway >2,000 AADT 1.15 Not calculated (4 ) Table 33. Reduce lane width from 12 ft to 10 ft (non-freeway).

46 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Crash Type Severity Facility Crash Type Volume Range CMF Error Source Standard Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway <400 AADT 1.05 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two- lane roadway >2,000 AADT 1.50 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway <400 AADT 1.04 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Undivided rural multilane roadway >2,000 AADT 1.38 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway <400 AADT 1.03 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Divided rural multilane roadway >2,000 AADT 1.25 Not calculated (4 ) Table 34. Reduce lane width from 12 ft to 9 ft or less (non-freeway). Crash Type Crash Severity Facility Type Volume Range dradnatS FMC Error Source All Fatal, injury* Freeway Not specified N/A (4 ) *Injury category includes both serious and minor injuries. Table 35. Reduce lane width (freeway). CMF Application Notes 1. The CMFs listed in Tables 33, 34, and 35 are included in the HSM, but they were derived from non-work-zone data so their potential applicability to a work zone situation is unclear. These values should be used with caution because they do not account for interactions with other work zone elements. 2. The freeway CMFs are applicable to lane widths in the range of 10.5 ft to 14 ft.

Catalog of Available Work Zone CMFs 47 Reduce Shoulder Width Description Shoulder widths may also be reduced during work zone activities. The HSM considers a 6-ft-wide lane as the baseline value for two-lane and multilane roadways. The HSM provides CMFs for reduced shoulder widths, but these CMFs do not consider interactions with lane widths, clear zone objects, or barriers that may occur in work zones. As a result, it is unclear if these CMFs can be directly applied because the impact of interactions with other work zone features has been not considered. Analysts need to weigh the values provided by this CMF with those presented in Tables 17 and 18 (that utilized limited work zone data) to assess which values would provide more reasonable results. CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed using work zone data. Base Condition: A 6-ft-wide shoulder. Available CMFs Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway <400 AADT 1.02 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway >2,000 AADT 1.15 Not calculated (4 ) Table 36. Reduce shoulder width from 6 ft to 4 ft (non-freeway). Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway <400 AADT 1.07 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway >2,000 AADT 1.30 Not calculated (4 ) Table 37. Reduce shoulder width from 6 ft to 2 ft (non-freeway).

48 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Crash Type Crash Severity Facility Type Volume Range CMF Standard Error Source Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway <400 AADT 1.10 Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway 400 to 2,000 AADT Not calculated (4 ) Single vehicle run off road, multiple vehicle head-on, side swipe All Rural two-lane roadway, undivided multilane roadway >2,000 AADT 1.50 Not calculated (4 ) Table 38. Reduce shoulder width from 6 ft to 0 ft (non-freeway). Crash Type All Crash Severity Fatal, injury* Facility Type Freeway Volume Range Not specified CMF Wis = paved inside shoulder width Standard Error Not calculated Source (4 ) *Injury category includes both serious and minor injuries Table 39. Reduce shoulder width (freeway). CMF Application Notes 1. The CMFs in Tables 36, 37, 38, and 39 are included in the HSM. However, they were derived from non-work-zone data, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 2. The freeway CMFs are applicable to shoulder widths in the range of 2 to 12 ft. Change Vertical Grade Description Vertical curves provide gradual changes between tangents of different grades. Grades or straight vertical sections are designed to be steep enough to allow for longitudinal drainage, but not so steep as to pose a danger to vehicles either through inadvertent increased speed downhill or through the difficulty of climbing uphill and posing safety risks where there are inadequate passing opportunities. CMFs Applicability to Work Zones: Likely applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Roadway with no vertical grade.

Catalog of Available Work Zone CMFs 49 Available CMFs Crash Type All Crash Severity All Facility Type Rural two- lane road Volume Range Not specified CMF 1.04 Standard Error Not specified Source (4 ) Table 40. Increase vertical grade by 1%. CMF Application Notes 1. The CMF listed in Table 40 was derived from past studies on non-work-zone roads, so the potential applicability to a work zone situation is unclear. These values should be used with caution. 2. The CMF included in the HSM can be applied to each individual section on the roadway, without respect to the sign (upgrade/downgrade). This CMF is included in the HSM in bold letters indicating a standard error of 0.1 or less. This value is based on roads with a 55 mph speed limit and a 12-ft lane width. Install Variable Speed Limit System Description Variable speed limit (VSL) systems dynamically change the posted speed limit in response to traffic conditions. The operation of VSL systems vary but frequently are configured to adjust speed limits in response to observed congestion, weather conditions, or work zone presence. While no work-zone-specific CMFs were located, a CMF is available for a permanent freeway deployment where the VSL was implemented primarily to provide speed harmonization and address congestion (37). CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Safety impacts for permanent locations with recurring congestion may not translate to a work zone where congestion may be more unpredictable. Base Condition: No VSL system present. Available CMFs Crash Type All Crash Severity All Facility Type Urban Interstate Volume Range Not specified CMF 0.92 Standard Error 0.04 Source (37 ) Table 41. Install VSLs. CMF Application Notes 1. While VSL systems may be used to manage work zone speeds, there were no studies available that examined safety effects in work zones specifically.

50 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook 2. The CMF in Table 41 was developed using data from a single permanent site in Missouri using an empirical Bayes analysis. While the CMF is reliable for the corridor that was studied, analysts should consider whether the results from a permanent installation would be trans- ferable to a particular work zone application. Reduce Ramp Acceleration/Deceleration Lane Length Description Work zone activities may decrease the length of freeway ramp acceleration or deceleration lanes. The HSM Supplement refers to acceleration and deceleration lanes as speed-change lanes (32). They are defined as the section of roadway area located between the marked gore and taper points of a ramp merge or diverge area, and on the same side of the freeway as the merge or diverge area (see Figure 12). CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. If the change in acceleration/deceleration Figure 12. Illustrative freeway segments and speed-change lanes (32).

Catalog of Available Work Zone CMFs 51 lane length was accompanied by installation of barriers or other changes that might interact with the speed-change lane length, these CMFs should be used with extra caution. Base Condition: Freeways with ramp entrances/exits located on the right side of the road. Available CMFs *Injury category includes both serious and minor injuries. Crash modification factors for entrance ramp acceleration lanes Crash modification factors for exit ramp deceleration lanes Crash Type All All Crash Severity Fatal, injury* Fatal, injury* CMF = ramp side indicator variable (1.0 if entrance/exit is on the left, otherwise 0) = Length of ramp entrance = AADT volume of ramp = ramp side indicator variable (1.0 if entrance/exit is on the left, otherwise 0) = Length of ramp exit Standard Error Not calculated Not calculated Source (32 ) (32 ) Facility Type Rural; one through lane Urban; one through lane Urban; two through lanes Rural; one through lane Urban; one through lane Urban; two through lanes Volume Range 0 to 7,000 vpd 0 to 18,000 vpd 0 to 32,000 vpd 0 to 7,000 vpd 0 to 18,000 vpd 0 to 32,000 vpd Table 42. Change acceleration/deceleration lane length. CMF Application Notes 1. The CMF for entrance ramps is applicable for deceleration lane lengths of between 0.04 and 0.30 miles (210 to 1,600 ft). The CMF for exit ramps is applicable for acceleration lane lengths of between 0.02 and 0.30 miles (106 to 1,600 ft) (see Table 42). 2. The CMF volume ranges indicate the conditions for which the CMF is considered valid. It is not known whether the CMF would produce reasonable results outside of these ranges. 3. The indicator variable for ramp side Ileft is associated with a positive regression coefficient. This sign indicates that a ramp entrance/exit on the left side of the through lanes is associated with an increase in crash frequency, relative to one on the right side. 4. CMFs for PDO crashes are also included in the HSM for these factors. Reduce Intersection Sight Distance Description Drivers acquire most of the information they use to control and navigate their vehicles visually. Appropriate sight distance approaching and within work zones is desirable from an operations and safety perspective. Likewise, work activities may reduce pre-existing sight triangles due to the presence of barriers and work vehicles. Reductions in sight distance could create negative safety impacts. While CMFs for increasing intersection sight distance are available, they do not

52 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook specify the magnitude of the sight distance change that occurred to generate the CMFs. The CMFs for reducing intersection sight distance were assumed to be the inverse of the CMFs for increasing the sight distance. CMFs Applicability to Work Zones: Possibly applicable. CMFs are assumed to be the inverse of increasing sight distance. CMFs were not developed with work zone data and do not include the magnitude of the sight distance reduction, so extreme caution should be used for work zone applications. Base Condition: Unclear. Studies did not quantify how much intersection sight distance was available before/after improvement, so the base condition is uncertain. Use of these CMFs is thus more problematic because severe sight distance reductions are treated the same as smaller ones. Available CMFs Crash Type All All All All Crash Severity Property damage only Injury* Fatal Injury* Facility Type Four-leg intersection Four-leg intersection Signalized intersection Signalized intersection Volume Range Not specified Not specified Not specified Not specified CMF 1.12 1.89 2.27 1.59 Standard Error 0.15 0.29 Not calculated Not calculated Source (22 ) (22 ) (38 ) (38 ) *Injury category includes both serious and minor injuries. Table 43. Reduce intersection sight distance. CMF Application Notes 1. The CMFs listed in Table 43 were developed by Elvik et al. (2004) and did not differentiate between signalized and unsignalized intersections (22). No other geometric information of the intersections was provided. 2. There was no information available on the degree of change to the intersection sight distance. The sight distances before and after the modification were not mentioned in any of these reports. 3. The standard errors listed are those for the original study, which examined increases in inter- section sight distance. Use Crossover Work Zone (Two-Lane, Two-Way Operation) Description This countermeasure applies to multilane divided facilities where one direction of travel is closed due to work activities. Traffic in both directions is merged into a single lane, and traffic in one direction is transitioned to the opposite side of the roadway. Figure 13 shows a typical appli- cation for a freeway crossover work zone from the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) (39).

Catalog of Available Work Zone CMFs 53 Figure 13. Typical freeway work zone crossover application from MUTCD (39).

54 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: Single lane closure in one direction. Available CMFs Crash Type All Crash Severity All Facility Type Four-lane divided highway Volume Range Not specified CMF 1.00 Standard Error 0.35 Source (40 ) Table 44. Use crossover work zone. CMF Application Notes 1. The CMF in Table 44 was developed using a simple before-and-after study. Even though the CMF indicates no safety impact, the standard error is extremely large, so the impacts of the crossover design are unclear at this time. Install Safety Edge on Temporary Roadway Description Pavement edge drop-offs on highways have been linked to many serious crashes, including fatal collisions. To mitigate vertical drop-offs, FHWA advocates installing Safety Edge on pavements during paving or resurfacing projects. Safety Edge provides a beveled edge to the pavement, which allows drivers who drift off the roadway to return to the pavement safely (see Figure 14). Even though this treatment showed a positive safety impact on regular roadways, its impact on temporary roadways has yet to be explored. Figure 14. Safety Edge on roadways.

Catalog of Available Work Zone CMFs 55 CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: Rural highways prior to resurfacing and installation of Safety Edge (unpaved and paved shoulders). Available CMFs Crash Type All Run off road Crash Severity All All Facility Type Rural two-lane principal arterial Rural two-lane principal arterial Volume Range 310 to 18,697 AADT 310 to 18,697 AADT CMF 0.943 0.937 Standard Error 0.057 (unadjusted) 0.057 (unadjusted) Source (41) (41) Table 45. Use Safety Edge on temporary roadway. CMF Application Notes 1. The CMFs listed in Table 45 were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution. 2. While none of these results is statistically significant, they do show a small, consistent benefit of the provision of Safety Edge on rural two-lane highways. 3. There were some observed differences between treatment and comparison sites for the period before resurfacing, which could confound the analysis results. Also, the sites with unpaved shoulders, where Safety Edge was expected to be most effective, had the lowest crash frequencies. This increased the variability in the data and made the statistical tests less powerful. These CMFs should be used with caution. Increase Retroreflectivity of Pavement Markings Description Pavement markings provide useful visual and navigational information to motorists. Previous research has shown that greater longitudinal pavement marking retroreflectivity levels increase drivers’ detection distance of this marking. However, increased visibility may also cause drivers to feel too comfortable during nighttime conditions, and drivers may then pay less attention or operate at unsafe speeds (42). CMFs Applicability to Work Zones: Possibly applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Base Condition: For rural roadways, the base condition is a retroreflectivity value less than or equal to 200 millicandela/square meter/lux (mcd/m2/lux) (43). For principal arterials, base condition is thermoplastic markings (ranging from 250 to 512 mcd/m2/lux for white edgeline, 252 to 401 mcd/m2/lux for white skiplines, 204 to 348 mcd/m2/lux for yellow edgeline, and 202 to 328 mcd/m2/lux for yellow centerlines) (42).

56 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Available CMFs Increase retroreflectivity of white edgeline, yellow edgeline, and yellow centerline Increase pavement marking retroreflectivity of white edge lines from X to Y mcd/m2/lux Increase pavement marking retroreflectivity of white skiplines from X to Y mcd/m2/lux Increase pavement marking retroreflectivity of yellow edge lines from X to Y mcd/m2/lux Increase pavement marking retroreflectivity of yellow centerlines from X to Y mcd/m2/lux Crash Type Several* All All All All All Crash Severity All All All All All All Facility Type Rural; multilane arterials and freeways Three-lane principal arterial Two-lane principal arterial Three-lane principal arterial Three-lane principal arterial Two-lane principal arterial Volume Range Not specified 2,752 to 47,572 2,752 to 47,572 2,752 to 47,572 2,752 to 47,572 2,752 to 47,572 Standard Error Not specified Not specified Not specified Not specified Not specified Not specified Source (43 ) (42 ) (42 ) (42 ) (42 ) (42 ) *Several = cross median, fixed object, frontal and opposing direction side swipe, head on, nighttime, run off road, side swipe, single vehicle. CMF Table 46. Increase retroreflectivity of markings from X to Y mcd/m2/lux. CMF Application Notes 1. There were no studies available that examined the safety effects of increasing retroreflectivity in work zones specifically. The CMFs listed in Table 46 were derived from non-work-zone roads, so their potential applicability to a work zone situation is unclear. 2. No standard errors for the CMFs were determined, so it is unclear how reliable these CMFs are. 3. It is important to check the base condition before using these CMFs to ensure that formulae are applied correctly. 4. The expected effect of letting the pavement markings degrade below the base level over the duration of the work zone can also be estimated using the formulae. In these cases, the Y (ending) value will be less than the X (beginning) value. 5. Cross-sectional regression equations were used to estimate the monthly target crash frequency. For multilane highways, the yellow pavement marking retroreflectivity parameter estimate was counterintuitive (42). Further research is needed to verify this relationship. Use Left-Hand Merge and Downstream Lane Shift (Iowa Weave) Description Some states will implement right lane closures followed by a lane shift when the activity area requires a left lane closure. This configuration is sometimes termed the “Iowa Weave.” Thus, every work zone would initially require that drivers merge from the right lane to the left lane, regardless of which lane is actually closed. Past studies have shown that this configuration is effective at

Catalog of Available Work Zone CMFs 57 slowing approach speeds, and it may improve driver expectations when approaching a work zone lane closure (44). Figure 15 shows an example conceptual traffic control plan of this strategy. CMFs Applicability to Work Zones: Directly applicable, data collected in work zones. Base Condition: CMFs are calculated relative to expected crashes with a conventional MUTCD right lane closure. No CMFs are available relative to a left lane closure. Available CMFs Crash Type All All Crash Severity All Fatal, injury* Facility Type Four-lane rural freeway Four-lane rural freeway Volume Range 20,120 to 35,864 vpd 20,120 to 35,864 vpd CMF 0.54 2.24 Standard Error Not calculated Not calculated Source (45 ) (45 ) *Injury category includes both serious and minor injuries. Table 47. Use Iowa Weave. CMF Application Notes 1. CMFs for the treatment listed in Table 47 were developed in a single study using data from 10 Arkansas Interstate work zones. A non-regression cross-sectional study design was used. Therefore, there were likely several uncontrolled sources of variation in the data. For example, no assessment of before-work-zone crash frequency was performed, so it is unknown whether the differences are due to the treatment or other site characteristics among the 10 sites. 2. No standard errors for the CMFs were determined, so it is unclear how reliable these CMFs are. Although the CMFs were computed using work zone data, they are based on limited information and should be used cautiously. Lower Posted Speed Limit Description Work zones may alter the geometric design and capacity of the roadway, so speed limits may be lowered in response to these changes. While no CMFs were identified that relate specifically to work zone speed limit reductions, several CMFs do exist that estimate safety effects of reduced speed limits in non-work-zone situations. Given that work zone speed limit reductions are often in response to changes in geometry at the site, it is uncertain whether these CMFs are transferable to work zones. Figure 15. Example traffic control plan for Iowa Weave (44).

58 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook CMFs Applicability to Work Zones: Questionably applicable. CMFs were not developed with work zone data, so caution should be used for work zone applications. Work zone speed reduction decisions may be driven by very different factors than non-work-zone speed reductions, so it is unclear if these may be used for work zones. Base Condition: Divided roadway with posted speed limit of 100 kph (62 mph) (46), freeways with the highest speed limit of 55 mph (47). Available CMFs Lower speed limit from 100 kph to 80 kph Lower posted speed by 5 mph Lower posted speed by 10 mph Lower posted speed by 15 to 20 mph Crash Type All All All All Crash Severity All All All All Facility Type Principal arterials, freeways, and expressways Urban and rural freeways Urban and rural freeways Urban and rural freeways Volume Range 3,100 to 50,300 Not specified Not specified Not specified CMF 0.86 1.17 0.96 0.94 Standard Error 0.079 (unadjusted) Not specified Not specified Not specified Source (46 ) (47 ) (47 ) (47 ) Table 48. Lower posted speed limit. CMF Application Notes 1. The CMFs listed in Table 48 were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution for work zones because reduced work zone speed limits are often connected to other changes in the roadway cross section. 2. Park et al. (2010) used 33 treatment sites and 44 comparison sites from Korean expressways to carry out the analysis (46). The results were statistically significant. 3. The study by Parker et al. (1997) was conducted from October 1985 to September 1992, when the maximum speed limit was 55 mph (89 kph) on freeways (47). The general types of sites included in the study were short sections, that is, 0.5-mile (0.8-km) segments in rural com- munities and 1-mile (1.6-km) sections in urban and rural communities. Because random selection and assignment of roadway sections to (a) experimental groups and (b) control groups for posted speed limit changes were not possible, these findings apply only to the study locations and cannot be generalized. Install Barriers Description Work zones often use barriers to provide protection for workers. While barrier use is a common work zone design attribute, there have been no prior studies that have developed CMFs for work zone barrier use. The HSM includes CMFs for barriers on freeways for non-work-zone situations, but there are questions about whether those CMFs would translate into a work

Catalog of Available Work Zone CMFs 59 zone environment. For example, the HSM CMFs assume a base case of no barrier being present. The roadside is likely to have many more potentially hazardous objects in close proximity to the travel lanes during work zone activities than when the road is under construction. As a result, these barrier CMFs likely underestimate the benefits of installing barriers versus not having barriers for work zone cases. Caution should be used in applying these CMFs. CMFs Applicability to Work Zones: Questionably applicable. The CMFs documented here were developed for non-work-zone conditions. The roadside environment is likely more hazardous during work activities, so potential safety benefits of barrier use are likely underestimated. Furthermore, the HSM defines a barrier as cable barrier, concrete barrier, guardrail, and bridge rail, and so the CMF values are influenced by non-work-zone barrier types. Base Condition: No barrier present in the median for median barrier CMF. No barrier present in the clear zone for outside lane barrier CMF. Available CMFs Crash Type All All Crash Severity Fatal and injury PDO Facility Type Freeways Freeways Volume Range Not specified Not specified CMF Standard Error Not specified Not specified Source (32 ) (32 ) Pib = Proportion of effective segment length with median barrier, Wicb = Distance from edge of inside shoulder to barrier face (ft). Table 49. Install median barrier. Crash Type Single vehicle Single vehicle Crash Severity Fatal and injury PDO Facility Type Freeways Freeways Volume Range Not specified Not specified CMF Standard Error Not specified Not specified Source (32 ) (32 ) Pob = Proportion of effective segment length with barrier on the outside, Wocb = Distance from edge of outside shoulder to barrier face (ft). Table 50. Install outside barrier (outside of rightmost travel lane). CMF Application Notes 1. The CMFs listed in Tables 49 and 50 were derived from past studies on non-work-zone roads, so their potential applicability to a work zone situation is unclear. These values should be used with caution for work zones since the base case (without barrier) may be more hazardous than for non-work-zones. These CMFs are best used to assess the relative trade-offs of positioning the barriers at different lateral distances from the travel lanes, once the decision to use barriers has been made on the basis of other factors (pavement edge drop-offs, proximity of workers, equipment to travel lanes, etc.).

60 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook 2. The barrier CMFs shown here also reflect results for cable barrier, guardrail, and bridge rail. As a result, they may not correctly estimate the safety impact of concrete barriers used in work zones. 3. For the median barrier CMF, the CMF is valid for Wicb values of between 0.75 and 17 ft. 4. For the outside barrier CMF, the CMF is valid for Wocb values of between 0.75 and 17 ft. Work Zone Features for Which No CMFs Exist Although this catalog of available CMFs is extensive, it does not encompass the entirety of work zone feature alternatives that practitioners can consider when designing and operating work zones. Through the conduct of this research, specific questions arose about the crash modification effect of a number of additional features for which no CMF data could be identified. However, in some cases, studies of the operational effects of these features were identified. These operational measures can provide useful insights into the potential safety benefits of the features. Summaries of key non-CMF research findings are provided for the following: • Circulating or mobile police enforcement • Pack enforcement • Legislation and signage for increased work zone fines • Programmatic public education and outreach campaigns for work zone safety • Project-specific public education and outreach campaigns for work zone safety • Enhancements to work space ingress and egress points Circulating or Mobile Police Enforcement Description Circulating patrols involve officers circulating through a work zone in marked or unmarked vehicles and are intended to extend the coverage of stationary enforcement in both time and space. Officers can identify a violator through measurements from a radar unit or by physically following the vehicle and noting the speed required to maintain a consistent following dis- tance. Circulating patrols prevent drivers from reducing their speed only at locations where they “know” the officer is located, but these patrols’ ability to reduce speed and increase driver awareness at a particular spot is limited. Circulating patrols can also serve roles in conjunction with speed enforcement in work zones, such as roadway monitoring, incident detection, and emergency response (9). It is likely that site-specific factors such as the length of the circulation route will influence the effectiveness of this feature and so would likely have less of an effect on safety than was previously reported for stationary police enforcement. Other Reported Safety Impacts Some studies have reported the effects of circulating enforcement in terms of speed reduc- tion. When compared with freeway scenarios without enforcement, studies from 1985 showed reductions in the order of 2 to 3 mph with circulating enforcement (48), and separate efforts from 1992 found 4.3 to 4.4 mph lower average speeds for cars and 4.3 to 5.0 mph lower average speeds for trucks (49). More recent data suggests that average speed reductions with circulating enforcement tend to be somewhat smaller (in the order of 2 to 4 mph) than those achieved with stationary techniques (9). Studies also show that the spatial effects of circulating patrols are limited. Halo (or lasting) effects for trucks were found that lasted for at least 1 hour after patrols departed from the work zone (49). However, cars traveled 2.4 to 3.0 mph faster and the percentage of fast-moving cars in the work zone increased after the police left the area. In addition, results from a 28-mile freeway

Catalog of Available Work Zone CMFs 61 segment in Michigan without a work zone showed that drivers had a tendency to reduce their speed by as much as 5 mph as they approached the patrol car, but accelerated back to their original speed or higher (up to 3 mph) after passing it. The study also concluded that the halo effect of police presence had negligible influence on speed selection by the motorists (50). Pack Enforcement Description In situations where active enforcement (i.e., identification and citation of traffic law violators) is desired, some agencies utilize a pack enforcement strategy. In this case, an officer in an enforce- ment vehicle (marked or unmarked) is positioned to identify traffic law violators and immediately communicates the description and license plate number of the violator to one or more officers at a downstream location for apprehension and citation. In this way, the speed reduction and traffic- calming effect of the upstream enforcement vehicle is maintained while the active enforcement efforts downstream contribute to a lasting change in driving behavior (9). In some cases the officer identifying violators provides an upstream overt presence to encour- age slowing at the back of the queue or work zone approach, but the officer can also be positioned at the work zone approach, within the work zone, or on an overpass (51). Other Reported Safety Impacts No studies evaluating speed reductions or safety effects associated with pack enforcement were found. However, some of the general advantages of pack enforcement have been summarized in previous publications (9, 51), including the following: • It is perceived to be “safer” than other enforcement strategies as it eliminates the pursuit of violators through work zones. • Violators can be identified at locations with concrete barriers, and then pulled over down- stream where shoulders are available. • Speed reduction effects achieved at an upstream location remain downstream. • Downstream citation ensures that credibility of enforcement is not lost. • Multiple officers are available to respond in case of work zone incidents. Conversely, some of the disadvantages of this strategy include increased costs, greater require- ment of law enforcement resources, and known violators traveling through the work zone until they reach the location of officers positioned downstream. Legislation and Signage for Increased Work Zone Fines Description As of June 2016, every state except Wyoming has implemented increased fines for certain violations occurring in work zones (52). Increased fines may apply to speeding, all moving violations, or all violations, depending on the state (see Figure 16). In 25 states, workers must be present for the increased fines to be in effect. The rationale for these increased fines is that the higher penalties would influence driver behavior, thereby improving safety. Other Reported Safety Impacts A 1997 Texas Transportation Institute (TTI) study attempted to assess the impact of increased fine legislation on the number of fatal crashes in long-term freeway work zones in the United States (53). Data from the Fatality Analysis Reporting System (FARS), a national database of all fatal crashes, was analyzed to determine if trends in fatal crashes in work zones

62 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook were significantly different between states with and without increased fines in work zones (3). At the time, only 14 states had at least 1 year of crash data following the implementation of the increased fine legislation. The data from these states was compared with data from the remain- ing 36 states that had not enacted legislation. The researchers found no significant difference between the trends in the number of fatal work zone crashes. Evaluations in Maryland, Minnesota, Pennsylvania, and Washington showed inconclusive impacts on total crashes, but those efforts were hampered by limited exposure data (53). Speed impacts were also generally not found to be significant. Although safety impacts remain inconclusive, an Oregon study found that increased fines can be an effective strategy for increasing driver awareness of work zone safety hazards, with 79% of drivers surveyed indicating that they reduced speed either “a lot” or “some” in response to signs (54). While violations were not found to be significantly reduced, increased awareness of work zone hazards was seen as a significant benefit. Programmatic Public Education and Outreach Campaigns for Work Zone Safety Description State DOTs and other agencies engage in public education and outreach aimed at improving work zone safety. Programmatic campaigns are typically intended to encourage drivers to reduce speeds, respect workers, drive attentively, and practice other good driving habits in work zones (55). These campaigns can be directed toward the general population or designed to target specific groups, for example young drivers. Examples of nationwide programmatic campaigns include the annual “National Work Zone Awareness Week,” a recurrent event aimed at motorist and worker safety and mobility issues in work zones, and “Turning Point: Roadway Work Zone Safety for New Drivers,” an effort that promoted safety messages to the general public, especially to new teen drivers. At the state level, efforts led by DOTs in coordination with other agencies are common practice, and almost every state has launched work-zone-related campaigns in recent years. Other Reported Safety Impacts Despite the wide use of programmatic campaigns for work zone safety throughout the United States, evaluations to measure their effects are not common. Evaluations tend to rely on qualitative opinions of drivers, and it is difficult to translate these results into crash reductions. A survey on state DOT work zone public outreach efforts indicated that only 2 of 42 agencies have conducted an evaluation of campaign effectiveness (55). The majority of survey respondents indicated that they believe work zone safety is one of the most important safety-related public outreach messages, but also expressed doubt about the adequacy of the scope of these efforts, citing difficulties to change driver behavior in the absence of additional funding for advertising Figure 16. Sample work zone sign showing increased fines.

Catalog of Available Work Zone CMFs 63 purchases. In 2013, a study in Saskatchewan conducted an advertisement effectiveness study to evaluate awareness of paid construction zone advertising, finding that 70% of the questionnaire respondents agreed that advertising messages have changed their behavior (56). Some general purpose campaigns have had significant impact. For example, an analysis of themed campaigns across the world indicated that drinking-and-driving campaigns reduced crashes by 13 to 14%, speeding campaigns reduced crashes by 8%, and other single campaigns reduced crashes by 10% (57). In general, media and public traffic safety education campaigns tend to have high benefit-cost ratios compared with other outreach efforts (58, 59). It should be noted, however, that the results are likely to be very site- and campaign-specific and thus cannot be directly translated into CMFs. Project-Specific Public Education and Outreach Campaigns for Work Zone Safety Description Project-specific campaigns are typically aimed at notifying the public about an individual highway project or phase of a project and can result not only in monetary savings by reduced road user delay costs but also in enhanced public support and agency credibility (55). More- over, the Final Rule on Work Zone Safety and Mobility requires that TMPs for significant projects include a public information plan to inform those affected by the project of the expected work zone impacts and changing conditions (60). Public information plans include both public awareness and motorist information strategies that range from press releases and media alerts to education campaigns and 511 traveler information systems (61). Public information plans may include, but are not limited to, information on the project characteristics, expected impacts, closure details, and commuter alternatives. Other Reported Safety Impacts Given that a public information component is required for the Final Rule on Work Zone Safety and Mobility, examples of a wide variety of project-specific campaigns can be found in the literature across the United States. However, the rule does not require a follow-up evaluation of public information efforts, and project-specific campaigns are difficult to evaluate from a safety standpoint due to several reasons, including the uniqueness of projects (making comparisons with other projects difficult), relatively short periods for safety analysis, and the difficulty to iso- late the public campaign effects from other factors (60). Examples of campaigns with significant results in terms of traffic diversion and delay savings include the I-405 project in Los Angeles related to the “Carmageddon” work zone (62), the I-15 Devore project also in California (63), and the “Hyperfix” project on I-65/70 in Indianapolis (64). Enhancements to Work Zone Ingress and Egress Points Description Work zone access and egress are critical to work zone safety, and data shows that vehicles entering and exiting the work zone can be a significant safety concern (65, 66). As part of federal rules to promote safety for workers and motorists in work zones, agencies should also address safe means for work vehicles and equipment to enter and exit traffic lanes and for the delivery of constructions materials to the work zone (67). Recommended practices to enhance safety at work zone access and egress locations are available, including incorporating construction access and egress locations into project plans, using ITS, and providing median access from cross-street overpasses (68).

64 Estimating the Safety Effects of Work Zone Characteristics and Countermeasures: A Guidebook Other Reported Safety Impacts Strategies to enhance safety at work zone access and egress locations have been implemented by several agencies, but only a few studies have been conducted to quantify or qualify the results of those implementations. Regarding the use of enhanced temporary traffic control devices and ITS, an access and egress survey indicated that DOTs and contractors believed that improper use of traffic control equipment can be a major contributor to confusion for truck drivers, equipment operators, and the traveling public (69). The survey identified “Upgrade/additional equipment, markings” as the best practice related to access and egress in closed (positive barrier between workers and traffic) and open work zones (no positive barrier and mostly used for short-term work zones). In the survey, additional equipment and upgrading equipment referred to signage, arrow boards, message boards, and any other additional equipment that a contractor can provide to either protect its jobsite or to communicate with the traveling public. Participants from the same studies also suggested improving construction trucks’ access and egress by extending acceleration and deceleration distances and by providing alternate routes. In addition, a survey of state DOTs that included responses from 20 officials from 14 states ranked the following as the most effective measures to improve safety of access and egress loca- tions in freeway and expressway work zones (70) (in descending order): • Incorporate access and egress locations into internal traffic control plans. • Build temporary ramps to provide median access from street overpass. • Improve lighting and visibility of access and egress points during nighttime work zones. • Use ITS technology to improve access and egress safety.