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13 This chapter presents findings from a literature review of countermeasure effectiveness with regard to pedestrian safety and traffic-speed management. Although studies explicitly docu- menting countermeasure effectiveness with regard to pedestrian safety are still uncommon, many studies have examined how countermeasures work to reduce traffic speed. Because traffic speed is a critical component of pedestrian injury severity, these studies are reviewed here. The chapter is organized into two sections: 1. research on pedestrian safety and traffic speed and 2. research on countermeasures that have been studied specifically with regard to reduc- ing traffic speed. Countermeasures covered include those classified as engineering, education, enforcement, and policy-related. Where available, findings from studies of countermeasures that reduce vehicleâpedestrian crashes and/or pedestrian injury severity as related to speed are presented; when studies have examined impacts on both pedestrian safety and traffic speed, this is discussed in the text. Additionally, the text covers some strategies that are promising or currently being tested, but for which empirical results are not yet available. Strategies were included in the review if the purpose of the treatment was specifically to reduce vehicle speeds and the treatment is appli- cable to roadways where pedestrian activity might be expected (e.g., residential streets) and/or if there is documentation from at least one source (academic or otherwise) that the treatment reduced vehicle speeds. These strategies are distinguished from those that are proven. When applicable, the text refers to additional information about these treatments in Chapter 3. Refer to Synthesis Scope and Approach (Section 1.3) for more information about the types of studies included in this review. 2.1 Pedestrian Safety and Traffic Speed This section presents a review of primarily academic studies documenting the relation- ship between traffic speed and pedestrian safety. This relationship is important because driver speed directly influences not only the injury severity of a pedestrian, but also the likelihood of a collision (Elvik et al. 2004, GÃ¥rder 2004, Aarts and Schagen 2006). The faster a driver is traveling, the less they can see at any one time (e.g., to notice and begin to slow for a crossing pedestrian), the greater the stopping distance required to stop with sufficient time to prevent a collision, and the lower the likelihood that the stopping distance will be available (AASHTO 2011, Tefft 2013, see Figure 2-1). Therefore, higher-speed roads need additional treatments to facilitate safe pedestrian travel. The studies included in this review examined the relationship between vehicle impact speed and pedestrian injury severity, uniformly finding that it is positive and nonlinear (i.e., that as speed increases, injury severity increases even faster) (Leaf and Preusser 1999, RosÃ©n and Sander C H A P T E R 2 Literature Review
14 Pedestrian Safety Relative to Traffic-Speed Management Figure 2-1. Pedestrian severe injury risk and driver field of vision and stopping distance at various speeds. (Data source: AASHTO 2011, Tefft 2013; Image source: Toole Design.) 2009, Richards 2010, RosÃ©n et al. 2011, Tefft 2013, Kroyer 2015, Martin and Wu 2018). Most studies on this topic evaluate pedestrian safety using at least 5 years of crash data and measure traffic speed via vehicle impact speed, typically derived from crash reconstruction efforts or posted speeds. Many relate a pedestrianâs risk of fatality to vehicle impact speed using an S-curve. Studies documenting the relationship between vehicle impact speed and pedestrian safety date back to the 1970s. The more recent studies (typically post 2000) are generally accepted as more robust because of the failure of many earlier studies to weight samples so that analyses were not based on biased datasets that overrepresented fatal and severe injuries. For example, of the 11 studies reviewed by RosÃ©n et al. (2011), only 2 adjusted for sample bias (Davis 2001, RosÃ©n and Sander 2009). As a result, the injury-risk curves derived from analyses conducted over the last two decades are typically less steep than those presented in earlier studies and may differ from more shocking figures that have been used to promote traffic safety in the past. However, the weighted sample research is considered more accurate, and the S-curves shown in the studies that accounted for the underreporting of minor and noninjury crashes are still quite steep. Even within the weighted sample studies, the estimated risk of pedestrian injury relative to impact speed varies slightly. For example, RosÃ©n and Sander (2009) reported that the risk of a pedestrian fatality at an impact speed of 30 mph was approximately 7%, and the risk of fatality at 40 mph was approximately 25%. When Tefft examined the four studies that all used weighted samples and adjusted their results to account for various factors and allow for comparison, he found slight variations in the fatality risk estimates (Davis 2001, RosÃ©n and Sander 2009, Richards 2010, Tefft 2013). Table 2-1 presents the ranges in impact speed (measured in mph) that correspond to various likelihoods of pedestrian fatality, per the seminal studies on the topic. One reason for the differences in injury-risk curves is that the studies used different datasets (e.g., from different countries, where certain risk factors may be more or less present) and slightly dif- ferent methodologies, such as including or excluding certain crash types, or accounting or not for confounding factors such as vehicle or age. For example, Tefft (2013) included pedestrians
Literature Review 15 struck by light trucks (i.e., pickup trucks, vans, and sport utility vehicles) in his dataset, whereas RosÃ©n and Sander (2009) excluded crashes involving these types of vehicles. It is ideal to con- trol for pedestrian age and vehicle type when possible, as research has found that pedestrian injury severity can be strongly influenced by/associated with both. For example, vehicle mass and design have clear impacts on pedestrian injury severity, with larger vehicles being associ- ated with more severe crashes (Henary et al. 2003, Lefler et al. 2004, Roudsari et al. 2004). In the United States, light trucks are common and are often involved in crashes that result in pedestrian injuries: In 2016, light trucks were involved in 42% of pedestrian fatalities that involved only one vehicle (NHTSA 2018). Tefftâs analysis also adjusted for victim age, finding that the average fatality risk for a 70-year-old pedestrian struck at any given speed was similar to the average fatality risk for a 30-year-old pedestrian struck at a speed approximately 12 mph higher (2013). In other words, older pedes- trians are at substantially greater injury risk at any given speed. Similarly, Martin and Wu (2018) and Richards (2010) found that for all speeds, the fatality risk was much higher for elderly pedes- trians than for other adults. Other studies, such as those by Kroyer (2015), Pitt et al. (1990), and Kim et al. (2008), suggest that it is not just seniors who are at greater risk of severe injury or fatality, but even adults ages 45 to 64 and young children. These findings suggest that reducing traffic speeds is especially important in areas where these populations are expected, such as near senior and community centers, assisted-living facilities, schools, and parks. Severe injury risk is also important to understand given the propensity for such injuries to alter someoneâs life substantially. Tefftâs research also examined the relationship between impact speed and pedestrian severe injury risk, finding a pedestrianâs risk of severe injury to be 40% at an impact speed of 30 mph and 73% at an impact speed of 40 mph (2013). Thus, while the risk of fatality at 30 mph may be relatively low (see Table 2-1), the risk of serious injury at that speed or higher is substantial for the average pedestrian age 15 or older. The cumulative literature clearly demonstrates that vehicle impact speeds strongly affect pedestrian injury severity and safety. In areas where pedestrian activity is expected, slowing vehicles will be an integral part of any strategy to improve pedestrian safety. 2.2 Countermeasures Review This section presents a review of countermeasures to reduce traffic speeds and improve pedes- trian safety. Given the current state of research on pedestrian safety and speed, this chapter includes information from a mixture of published academic literature and âgrayâ literature, Risk of Fatality (%) Impact Speed (mph)* 10 24 to 33 25 33 to 41 50 41 to 48 75 48 to 55 90 54 to 63 *Ranges correspond to the results from the four studies, which each used a slightly different methodology. Sources: Davis 2001,RosÃ©n and Sander 2009,Richards 2010, Tefft 2013. Table 2-1. Pedestrian fatality risk associated with various impact speeds.
16 Pedestrian Safety Relative to Traffic-Speed Management such as reports from government entities. Throughout this chapter, the terms âcountermeasureâ and âtreatmentâ are used synonymously. Few evaluations of countermeasures (peer-reviewed or otherwise) directly measure effects on pedestrian safety. However, a relatively large body of evidence indicates the effectiveness of vari- ous countermeasures regarding reducing vehicle speeds. Given that pedestrian safety is closely related to traffic speed, as discussed above, treatments proven effective or shown as promising at reducing traffic speeds are included in this review. Topics covered in the countermeasure review include â¢ Engineering countermeasures, â¢ Enforcement countermeasures, â¢ Education and marketing campaigns, and â¢ Policies and legislative efforts necessary to support any of the above. 2.2.1 Background on Study Methods and Limitations There are a few different ways researchers evaluate a countermeasureâs impact on safety. The most common way to measure safety is to measure the change in the number of crashes over time. Because this synthesis focuses on traffic-speed management, most of the studies discussed document changes in traffic speed, rather than crashes. However, if a study also documented changes in vehicleâpedestrian crashes in particular, this is articulated in the review. The two most commonly used measurements are mean travel speed and 85th percentile speed. Another measurement sometimes used is top-end (also called high-end) speeders: drivers traveling at least 10 mph above the speed limit. Most studies included in this review measure the impact of countermeasures via a beforeâafter or cross-sectional approach; some studies use both to control for general trends that may be occurring throughout a specific area. Studies that include a cross-sectional approach typically include a crash analysis. Although more data can lead to more robust findings, many of the existing studies on countermeasures to improve pedestrian safety include only a few study sites and only a few rounds of data collection. Some beforeâafter studies report two rounds of postinstallation data to measure the long-term impacts of a treatment, but in most cases, this information is not collected. Many studies collect postinstallation data only a few weeks or months after a treatment is installed (FHWA 2014). The effectiveness of treatments that do not force or require vehicles to slow down may decline over time as drivers become more accustomed to such treatments. 2.2.2 Using the Countermeasures Review The following discussion of countermeasures includes a description and summary of each countermeasureâs effectiveness at reducing traffic speed and/or improving pedestrian safety. Because of differences in study methods and data collection bounds and periods, as well as the fact that many studies lack additional details about context and many treatments are not well studied, it is difficult to determine the most effective treatment for a given roadway environment. Even across studies of the same type of treatment, there can be wide ranges in the reported effects. Therefore, this synthesis reports only on general trends in treatment effectiveness; engineering judgment remains a key aspect of selecting the appropriate treatment for a situation. In general, treatments are listed individually or grouped with similar treatments. However, there are times when countermeasures are studied as parts of a suite of treatments, rather than alone. For example, a city may install a series of chicanes and speed humps along the same street
Literature Review 17 segment to reduce driving speeds in a residential area. Thus, a summary of existing literature on the impacts of combinations of treatments is presented following the section on the individual treatments. For additional guidance on how to choose and where to apply the engineering treat- ments, as well as information on treatment installation costs, refer to NCHRP Project 15-63, âGuidance to Improve Pedestrian and Bicycle Safety at Intersections,â (in progress) and the Pedestrian and Bicycle Safety Guides and Countermeasure Selection System (PedSafe and BikeSafe). Additional information on countermeasures more generally (i.e., not solely related to speed) can be found in multiple sources, including FHWAâs 2008 Toolbox of Countermea- sures and Their Potential Effectiveness for Pedestrian Crashes and Retting et al.âs 2003 counter- measure review. 2.2.3 Engineering Countermeasures Treatments with Vertical Deflection Traffic-calming treatments that integrate vertical deflection have proven to be the most effec- tive engineering treatments for reducing speed. In this context, vertical deflection refers to treat- ments that physically raise the height of the roadway in a specific area, which typically require vehicles to slow as they drive over them. These types of treatments include speed humps, speed lumps (also called speed cushions), and speed tables/raised crossings. Studies have shown that engineering treatments with vertical deflection are more effective at reducing vehicle speeds than engineering treatments with horizontal deflection and enforcement strategies, such as ASE cameras (Mountain et al. 2005, FHWA 2014, Gonzalo-Orden et al. 2016). Raised traffic-calming treatments have also been found to improve safety for motorists (Mountain et al. 2005). How- ever, because these treatments are so effective, they tend to be used on local or low-volume roads more than other roads where mobility is a higher priority, a fact reflected in the studies presented here. Speed Humps and Speed Lumps/Cushions. Speed humps and speed lumps/cushions are two commonly used traffic-calming treatments with vertical deflection. Speed humps provide a continuous raised area, typically 12 to 14 ft in length, whereas speed lumps/cushions are speed humps with cutouts to allow wheels of large vehicles (e.g., emergency response vehicles and buses) to easily pass through (see Figure 2-2). These treatments are typically applied along roads with posted speeds of 20 to 25 mph. Figure 2-2. Speed humps (left) and lumps (right) on residential streets. (Source: Toole Design.)
18 Pedestrian Safety Relative to Traffic-Speed Management The effectiveness of these treatments to reduce vehicle speeds is well documented. In general, speed humps and speed lumps have been found to be similarly effective, with the latter preferred along emergency response vehicle routes. A review of speed lumps and speed humps found that in comparison to control sites, speed lumps reduced 85th percentile speeds by 25% (9 mph), which was comparable to that of speed humps (23% or 8 mph) (Gulden and Ewing 2009). These findings are on par with most studies of these two treatments, which have found postinstallation reductions of 5 to 8 mph in 85th percentile speeds (FHWA 2014, Agerholm et al. 2017). For example, along the City of Alexandriaâs West Abingdon Drive and Martha Custis Drive, two collector streets with one lane in each travel direction, 85th percentile speeds decreased by 21% to 30% (6.5 to 10.5 mph) after speed lumps were installed. Along both streets, the speed lumps reduced 85th percentile speeds to align more closely with the posted speed (25 mph) (City of Alexandria n.d.). The San Francisco Municipal Transportation Agency (SFMTA) found similar results along eight nonarterial residential streets where residential traffic-calming measures were installed between 2011 and 2015 (City and County of San Francisco 2016). At locations where speed humps were installed, the 85th percentile speed decreased by 23%, and vehicles traveling over 30 mph decreased by 87%. Ponnaluri and Groce (2005) also found that speed lumps reduced the number of vehicles traveling above the speed limit. Speed humps are one of the few treatments for which the direct effect on pedestrian safety has been studied. Rothman et al. (2015) estimated a crash modification factor (CMF) of 0.74 for speed humps on local roads; among crashes involving children (ages 0 to 14), the CMF is 0.56. This study used a beforeâafter quasiexperimental design and was conducted in Toronto; it is unclear whether vehicle or pedestrian volumes changed, or if risk was displaced to other areas. Using a matched caseâcontrol study, Tester et al. (2004) evaluated the impact of speed hump installation specifically on childâpedestrian safety. A multivariate conditional logistic regression analysis revealed that speed humps were associated with a 53% to 60% reduction in the risk of injury or death among children struck by a vehicle in their neighbor- hood (adjusted odds ratio = 0.47) after controlling for race and ethnicity (Tester et al. 2004). As with many traffic-calming treatments, the effect of speed humps is localized, and the greatest reductions in speeds have been found to occur closest to the treatment (Agerholm et al. 2017). Speed humps have also been found to be effective when used in combination with curb extensions (Ewing 1999, Gitelman et al. 2017). For more information on curb extensions, see the section on neckdowns, bulb-outs, curb extensions, and chokers; for more information on the study of combined treatments, see the Engineering Countermeasure Combinations section. Speed Tables and Raised Crossings. A speed table is a longer and wider speed hump (typi- cally 22 ft long) with a flat top and ramps going up either side (see Figure 2-3). Similar to speed humps and speed lumps, speed tables have proven effective at reducing vehicle speeds. Speed tables are often used in conjunction with marked crosswalks to provide raised crossings for pedestrians and, when used at intersections, to reduce turning speeds for vehicles. Speed tables have been shown to reduce 85th percentile speeds and mean speeds by 3 to 11 mph (FHWA 2014). In one Australian study, reductions in 85th percentile speeds as high as 40% were documented (Hawley et al. 1992). Huang and Cynecki (2001) measured the impacts of raised crosswalks in North Carolina and observed reductions in 50th percentile speeds (ranging from 2.5 to 12 mph) across the three study sites; for two of these sites, the reductions were statistically significant (p < 0.05). In Spain, Gonzalo-Orden et al. (2016) measured the impact of two raised crosswalks by comparing speed profiles of vehicles traveling along a roadway with two raised crosswalks compared to a similar roadway with regular marked crosswalks. The researchers found that two raised crosswalks, which were approximately 1,700 ft (520 m) apart, performed
Literature Review 19 similarly and were associated with 50th and 85th percentile speeds 12 mph lower than the road- way with regular marked crosswalks. To date, there is little research on the impact of this treatment directly on pedestrian safety. However, Elvik and Va (2004) found that raised crossings installed with a marked crosswalk were associated with a nearly 45% reduction in vehicleâpedestrian crashes (CMF: 0.55). Simi- larly, Chen et al. (2013) derived a CMF of 0.45 based on an examination of beforeâafter data from 601 speed table locations (referred to as speed humps in the study) along road segments in New York City. The treatments typically were installed along one-lane residential streets. Speed tables have also been found to be effective when used in combination with speed humps (Gitelman et al. 2017); for more information, see the Engineering Countermeasure Combinations section. Treatments with Horizontal Deflection In contrast to treatments with vertical deflection, which force vehicles to slow down, treat- ments with horizontal deflection encourage slower speeds by laterally shifting the line of travel. These treatments include chicanes, neckdowns, curb extensions, chokers, raised center islands, and mini traffic circles. Although treatments that integrate horizontal deflection are less commonly studied than treatments with vertical deflection, the former have been proven effective in many situations and are widely used in many U.S. cities. Importantly, treatments with horizontal deflection include options appropriate for arterial or other high-volume road- ways. Research indicates that, in general, horizontal treatments can be more effective than ASE, but are typically less effective than treatments with vertical deflection (FHWA 2014; Mountain et al. 2005). Chicanes. Chicanes are small, raised islands used to narrow the roadway and laterally shift traffic. Typically, chicanes alternate between sides of the road, but occasionally are placed on only one side of the road (see Figure 2-4). The FHWA (2014) reported reductions in 85th percentile speeds ranging from 3 to 9 mph after the installation of chicanes. Ewing (1999) found that the 85th percentile speed reductions associated with chicanes averaged 14% and were on par with treatments with vertical deflections. The Traffic Advisory Unit (1997) in London reviewed speed data for 142 chicanes and found that chicanes reduced mean and 85th percentile speeds by 12 mph. Figure 2-3. Raised crossings in residential (left) and commercial (right) environments. (Source: Toole Design.)
20 Pedestrian Safety Relative to Traffic-Speed Management Agerholm et al. (2017) also used a beforeâafter study to compare the impacts of chicanes and speed humps on vehicle speeds in Denmark. The authors found that the two treatments were similarly effective at reducing mean travel speeds and 85th percentile speeds. The chicanes were associated with a 3-mph reduction within 410 ft of the treatment and a 4-mph reduction within about 250 ft of the treatment. The authors noted that there was a slightly greater variation in speeds at sites with the chicanes compared to those with the speed humps, although only two sites with chicanes were included in this study. This review found no research on the impact of this treatment directly on pedestrian safety. Mini Traffic Circles. Mini traffic circles are small, circular raised islands placed in the middle of uncontrolled intersections of residential streets (see Figure 2-5). Mini traffic circles are best suited for streets with speed limits less than 30 mph (FHWA 2010). Figure 2-4. Chicanes on both sides of the street (left) and one side of the street with a mini traffic circle (right). (Source: Toole Design.) Figure 2-5. Mini traffic circles in residential areas. [Source: www.pedbikeimages.org, Dan Burden (left) and Toole Design (right).]
Literature Review 21 Ewingâs (1999) review of 45 sites across the United States found that 85th percentile speeds reduced by an average of 4 mph after traffic circles were installed. A study of traffic circles along 25 mph roads in Clark County, WA, found that after installation, 85th percentile speeds decreased from 32 to 25 mph and mean speeds decreased from 28 to 22 mph (Zegeer et al. 2013). FHWA and the City of Seattle also indicate that mini traffic circles can be used to reduce traffic speeds in residential areas (FHWA 2010, U.S. Roads 1998). This review found no research on the impact of this treatment directly on pedestrian safety. However, an analysis of 4 years of crash data from Seattle found a notable decrease in crashes after the City installed over 100 neighborhood traffic circles at nonarterial intersections. After the traffic circles were installed, there was an 89% decrease in crashes and a 97% decrease in traffic-related injuries (U.S. Roads 1998), although the study does not state the degree to which the reduction in crashes was due to a reduction in conflicts versus speed. Modern Roundabouts. Modern roundabouts are circular raised islands that move traffic in one direction, control speed on entry, and are placed in the middle of uncontrolled intersections of larger streets, typically either collectors or arterials (see Figure 2-6). They are designed to accom- modate more traffic than mini traffic circles and can be designed to accommodate higher speeds. Retting et al. (2003) reviewed multiple roundabout studies and found a consistent, dramatic reduc- tion in pedestrian crashes when intersections with traffic signals or stop signs were converted to roundabouts. Brude and Larsson (2000) found that the conversion of a signalized intersection to a single-lane roundabout was associated with 3 to 4 times fewer crashes than otherwise expected, but the conversion to a two-lane roundabout showed no difference in pedestrian crash outcomes. Lane and Road Reconfiguration Road Reconfiguration (Road Diets or Rechannelizations). Road reconfiguration projects (commonly known as road diets or rechannelizations) involve removing at least one travel lane from a roadway and repurposing that space for other uses, typically to add bicycle lanes, medians, turn lanes, or on-street parking (see Figure 2-7). The most common lane reconfiguration involves turning a four-lane roadway to a two-lane roadway with a two-way left turn lane (center turn lane). Evidence from academic studies and city reports indicates that road diets, particularly when coupled with other treatments, can effectively reduce vehicle speeds and improve pedestrian safety. Figure 2-6. Modern roundabout. (Source: www. pedbikeimages.org, Carl Sundstrom.)
22 Pedestrian Safety Relative to Traffic-Speed Management Corkle et al. (2001) and Knapp and Giese (2001) reported reductions in mean travel speeds and 85th percentile speeds ranging from 1 to 4 mph after studying four- to three-lane road diets in urban areas. Gates et al. (2007) reviewed 20 sites with lane reductions and reported reductions in mean speeds at nearly all sites, although reductions were statistically significant at only three sites. The authors also recorded reductions in 85th percentile speeds at 15 sites. Thomas (2013) synthesis of six studies on road diets concluded that, in general, road diets effectively reduce vehicle speeds, and in many cases, reduce crashes. Her research indicates that the largest safety benefits may occur on roadways with a high density of driveways, multilane crossings, and a history of severe crashes and/or vehicleâpedestrian crashes, and speeding. She also found that, in many situations, vehicle volumes are not diminished by road reconfiguration projects. Chen et al. (2013) was the only study to review changes in vehicleâpedestrian crashes; the study reviewed 460 sites and found that vehicleâpedestrian crashes reduced by 53% at treatment sites, compared to nearly 4% at control sites. The authors derived a CMF of 0.38 for vehicleâpedestrian crashes. At intersections, however, vehicleâpedestrian crashes increased by nearly 4% at treatment sites and decreased by 18% at control sites. This trend was similar across all types of crashes at intersections with road diets, not just those involving pedestrians. The authors did not control for changes in vehicle or pedestrian volumes, so increased volumes may have influenced these results. Studies of numerous lane reduction projects in Washington State have shown significant decreases in traffic speeds and, in some cases, increased pedestrian safety. For example, a proj- ect in University Place resulted in a 13% decrease in average traffic speeds, a 60% reduction in total crashes, and consistency in the number of pedestrian crashes, despite increased pedestrian volume. The City of Seattle has completed numerous road diets that have reduced traffic speeds, including along Rainier Ave S, Stone Way N, NE 125th Street, NE 75th Street, and Nickerson Street. At each of the aforementioned sites, 85th percentile speeds decreased substantially, and many were also associated with large decreases in the percentage of drivers speeding in general, as well as those speeding more than 10 mph over the speed limit [Seattle Department of Trans- portation (SDOT) 2010, SDOT 2011, SDOT 2013, SDOT 2015, SDOT 2017a]. The decreases in 85th percentile speeds ranged from 3 to 7 mph. The percentage of top-end speeders decreased by at least 75% at all sites (SDOT 2010, SDOT 2011, SDOT 2015). A few projects were associated with decreases in pedestrian crashes (Rainier Ave S, Stone Way N, and NE 75th Street), which ranged from 9% to 100% (SDOT 2010, SDOT 2015, SDOT 2017a). Additionally, a beforeâafter report of the Stone Way N project found that traffic was not diverted to parallel neighborhood streets, Figure 2-7. Before (left) and after (right) a street reconfiguration project in Seattle, WA. (Source: Toole Design.)
Literature Review 23 which experienced a reduction in average daily traffic (ADT) volumes (SDOT 2010). Some of the road reconfiguration projects included the addition of pedestrian crossing improvements. For example, Rainier Ave S was coupled with a speed-limit reduction and increased enforce- ment and is discussed further in the Engineering Countermeasure Combinations section. Neckdowns, Bulb-outs, Curb Extensions, and Chokers. Neckdowns, bulb-outs, curb extensions, and chokers physically narrow the roadway width at intersections or in the middle of the block, often by extending the sidewalk (see Figure 2-8). This physical narrowing of the roadway encourages slower traffic speeds. If combined with a pedestrian crossing, this treatment also reduces pedestrian exposure by reducing the crossing distance. Similarly, if combined with a reduced curb radius, curb extensions can operate as horizontal deflection. Although these treatments are recommended in many traffic-calming guides and considered an effective tool in many cities (see Chapter 3), their effectiveness is not well established in the literature. Research published on neckdowns has found mixed results. Some studies documented slight increases in 85th percentile speeds post installation, whereas other studies noted decreases in 85th percentile speeds after neckdowns/curb extensions were installed, two of which also noted decreases in mean travel speeds (Ewing 1999, Corkle et al. 2001). A driver simulator study by Bella and Silvestri (2015) found that curb extensions were associated with a significantly larger distance between where deceleration began and a pedestrian crossing, compared to no treat- ment, advance yield markings, and parking restrictions (p < 0.000). Many jurisdictions, including Arlington County, VA; Berkeley, CA; Cambridge, MA: Eugene and Portland, OR; Montgomery County, MD; and Tempe, AZ, have implemented neckdowns and curb extensions to reduce vehicle speeds and improve pedestrian safety. Brattle Street in Cambridge was reconstructed in 2010 to add curb extensions, chicanes, and crossing islands at intersections (City of Cambridge 2012). Speed studies conducted before and after the instal- lation of the traffic-calming measures found that the 85th percentile speed did not change significantly, but there was a significant reduction in the percentage of drivers traveling 25 to 30 mph, and an increase in the number of drivers traveling at speeds below 25 mph. In a survey conducted among residents 2 years after the project was constructed, the City found that nearly 60% of respondents felt that the changes improved pedestrian safety (N = 417). This review found little research on the effect of these treatments directly on pedestrian safety. King (1999) found that curb extensions were associated with a reduction in vehicleâpedestrian Figure 2-8. Neckdown (left) and midblock curb extension with raised center median (right). (Source: Toole Design.)
24 Pedestrian Safety Relative to Traffic-Speed Management crash severity at some intersections in New York City, but a CMF has not yet been developed. However, the treatment is considered effective enough for many cities to use it as a key element of slowing driver speed. Raised Medians and Pedestrian Crossing Islands. Raised medians and center islands can be used to narrow the roadway width and provide a refuge area for pedestrians at crossing loca- tions (see Figure 2-9). Two studies of this treatment in urban areas noted reductions in 85th percentile speeds of 3 to 8 mph after installation [Ewing 1999; New York City Department of Transportation (NYCDOT) 2004]. One of the studies also noted a 2-mph reduction in mean travel speeds (NYCDOT 2004). Medians and pedestrian crossing islands are associated with increased pedestrian safety. Gan et al. (2005) established a CMF of 0.75 for vehicleâpedestrian crashes for raised medians. CMFs for raised medians with marked crosswalks at unsignalized intersections have been estimated at 0.54 to 0.61 for vehicleâpedestrian crashes (Zegeer et al. 2002, FHWA 2008). Lane Narrowing with Pavement Markings. Although more common in rural areas, the practice of using pavement markings to create the effect of a narrowed travel lane in order to reduce vehicle speeds is used in some cities (see Figure 2-10). Research on the effectiveness of this treatment in urban areas has yielded mixed results. A study by VHB (2008) found a 4-mph reduction in mean vehicle speeds at a four-lane intersection, whereas Lum (1984) observed no change in traffic speeds after the treatment was installed in a residential area. Ewing (1999) observed that lane narrowing had minimal impact on 85th percentile speeds. Similarly, NCHRP Synthesis 498 (Thomas et al. 2016) suggests that improvements associated with narrowing lane widths are likely negligible. The effectiveness of narrowing lane widths on traffic speeds and pedestrian safety likely depends on several factors, such as number of lanes, shoulder width, and the provision of additional pedestrian safety improvements (Boodlal et al. 2015). It is also possible that the material used to narrow the lane would affect its effectiveness; for example, narrowing a street by using flexposts, as opposed to paint, may have a stronger effect on a driver because of the increased risk from hitting the posts. More research is needed to determine the effectiveness of various strategies to reduce vehicle speeds via narrowed lane widths. This review found no studies on the effect of lane narrowing directly on pedestrian safety. Figure 2-9. Raised medians with pedestrian crossings. (Source: Toole Design.)
Literature Review 25 Curb Radius Reductions. Curb radius reductions require drivers to make sharper turns and, ideally, drive slower when turning a corner (see Figure 2-11). This review found no studies on the impact of curb radius reductions on pedestrian safety or vehicle speeds in the United States. However, this treatment is still considered promising given the principles of geometry and its impact on driver behavior. ITE (2010) suggests that reducing curb radii can improve pedestrian safety by reducing turning vehicle speeds, improving visibility between drivers and pedestrians, and reducing the distance pedestrians must travel to cross the street. In Toronto, Zangenehpour et al. (2017) reviewed 144 hours of video data at two intersections where curb radius reductions were installed. Their analysis showed no significant changes in vehicle speeds, however, the authors observed notable decreases in the rates of low-, medium-, and high-risk conflicts between turning vehicles and pedestrians. Conflicts were categorized based on the post-encroachment time (PET), which is the amount of time between when the first user left a common spatial zone and the second road user arrived in the common spatial Figure 2-10. Lane narrowing using white paint. (Source: Toole Design.) Figure 2-11. Corner retrofitted to have a reduced curb radius. (Source: Toole Design.)
26 Pedestrian Safety Relative to Traffic-Speed Management zone. High-risk conflicts included those with a PET of less than 1 sec, medium-risk conflicts had a PET between 1 and 3 sec, and low-risk conflicts had a PET between 3 and 5 sec (Zangenehpour et al. 2017). Signs and Signals Speed feedback signs and speed-activated speed limit signs. A speed feedback sign displays the travel speed of drivers as they pass by the sign (see Figure 2-12), whereas a speed-activated speed limit sign displays the speed limit for vehicles exceeding a specific speed. A study of two speed-activated speed limit signs and two speed feedback signs along main roads through small communities in Iowa found both treatments to be effective (Hallmark et al. 2013). Speed feed- back signs were associated with an 8-mph decrease in mean speeds and a 9-mph decrease in 85th percentile speeds. The percentage of vehicles traveling 5, 10, or 15 mph over the limit decreased by 33%, 53%, and 71%, respectively. Speed-activated speed limit signs were associ- ated with a 6-mph decrease in mean speeds and 7-mph decrease in 85th percentile speeds. The decreases in the percentage of vehicles traveling 5, 10, or 15 or more mph over the posted speed limit were 25%, 40%, and nearly 53%, respectively. Speed reductions persisted 12 months after installation, although the reductions were not as dramatic. A study of three speed-activated speed limit signs on collector streets in Colorado reported 4-mph reductions in 85th percentile speeds (FHWA 2014). A separate study of three speed feedback signs in Texas reported decreases in mean speeds (7 mph) and 85th percentile speeds (3 mph) 4 months after installation (Ullman and Rose 2005). This study found no research of the impact of speed feedback signs or speed-activated speed limit signs directly on pedestrian safety. In-Street Pedestrian Crossing Signs. This category refers to the placement of Yield to Pedes- trian signs (MUTCD R1-6) in the center and/or on the side of lower-speed roadways, which has been associated with reductions in vehicle speeds (see Figure 2-13). For example, Kamyab et al. (2003) found that after installing multiple in-street Yield to Pedestrian signs along a center median of one two-lane roadway in a rural area (see photo on left in Figure 2-13), speed-limit compliance increased from 31% to 54% and mean speeds decreased by approximately 5 mph (p < 0.05). After installing one in-street sign at six locations in North Dakota, Gedafa et al. (2014) observed that mean speeds reduced significantly from 1 to 5 mph (p < 0.05) at four of the six sites. A study of the impacts of installing one in-street sign in Iowa revealed that the in-street sign was effective at reduc- ing vehicle speeds at only one of the three sites. The site that was associated with speed reductions had an ADT of 5,400, whereas the other two sites had ADTs of 7,400 and 25,000. Figure 2-12. Speed feedback sign. (Source: Toole Design.)
Literature Review 27 More recently, a gateway strategy using these in-street signs (three R1-6 signs placed in the street perpendicular to the direction of travel) has been tested. Van Houten and Hochmuth (2017) examined the impact of the gateway treatment on vehicle speeds and found that they declined post installation at all 10 study sites. The reduced speeds persisted throughout the study period (nearly one year). The average speed reduction was 4 mph; however, some study sites were associated with reductions of nearly 10 mph. Speed measurements and results associated with this study were not dependent on the presence of a pedestrian. To date, there are no studies on the impact of in-street pedestrian crossing (R1-6) signs directly on pedestrian safety. Signal Timing. Some cities are adjusting signal timing to promote slower traffic speeds. For example, when the City of Seattle reduces the speed limit along a corridor with signal- ized intersections, signal timing is adjusted to the new design speed to encourage vehicles to travel at the new posted speed (Le 2018). New York City also uses signal timing as a low-cost strategy to encourage slower vehicle travel speeds (City of New York 2014), and the National Association of City Transportation Officials (2013) recommends adjusting signal timing in downtown areas as a means of encouraging slower driving speeds. Cities in Europe and in the United States are exploring the use of âresting on redâ to encourage slower traffic speeds (see Chapter 3). Engineering Countermeasure Combinations In some situations, jurisdictions have chosen to implement multiple treatments as part of one traffic-calming project. The literature on this topic indicates that, in general, implement- ing multiple types of engineering treatments at once is an effective strategy for reducing vehicle speeds and improving pedestrian safety. In Alexandria, VA, curb extensions, neck downs, speed cushions, and crosswalks were installed on Russell Road, a two-lane arterial (see Figure 2-14). A postinstallation assessment revealed that 85th percentile speeds decreased by 21% in one direction and 18% in the other direction (City of Alexandria, n.d.). Along Brattle Street in Cambridge, MA, curb extensions, chicanes, and pedestrian crossing islands were installed as part of a City-led traffic-calming project (City of Cambridge 2012). After installation, 85th percentile speeds decreased from 31 to 30 mph, the percentage of drivers traveling 25 to 30 mph decreased, and the percentage of drivers traveling 21 to 25 mph increased. Figure 2-13. Traditional in-street pedestrian crossing sign treatment (left) and gateway deployment (right). [Source: Toole Design (left) and Ron Van Houten (right).]
28 Pedestrian Safety Relative to Traffic-Speed Management Also in Cambridge, a combination of curb extensions, a raised crosswalk, and a raised inter- section was constructed along Granite Street, a neighborhood collector with a speed limit of 30 mph. The City conducted a speed study before and after the installation of the engineer- ing treatments and found that vehicle volumes remained consistent, 85th percentile speeds decreased from 28 to 24 mph, and the percentage of vehicles traveling above 25 mph decreased from 39% to 14% (Zegeer et al. 2013). Montgomery County installed five raised traffic islands and six curb extensions and reduced the curb radius at one intersection along an arterial street. Speed studies conducted before and after the treatments were installed indicated that the mean speed decreased from 30 to 24 mph, the highest speed decreased from 44 to 38 mph, and the 85th percentile speed reduced from 32 to 27 mph (Zegeer et al. 2013). In 2014, Seattle launched a project to improve safety along Rainier Avenue South by reduc- ing excessive speeding, improving conditions for pedestrians, and enhancing intersection safety (SDOT 2017a). The City reconfigured the street from four to three lanes, including two travel lanes and a center two-way left turn lane; provided one leading pedestrian interval and left-turn signals; adjusted signal timing; and reduced the speed limit from 30 to 25 mph (see Figure 2-15). For a few weeks after the design and operation changes were installed, the City also increased enforcement along the corridor. Post-construction evaluations indicated that the project reduced traffic speeds and vehicleâpedestrian crashes. The percentage of drivers speeding decreased by more than 25%, and the percentage of top-end speeders decreased by more than 70%. The percentage of vehicleâpedestrian crashes decreased by 9%, although the crash data included only one year of data post project completion. A few studies have specifically examined the effectiveness of treatments on their own versus in combination with other treatments, finding, not surprisingly, that the combinations were generally more effective. For example, neck downs and medians were found to be more effective when implemented together (Corkle et al. 2001), and marked crossings were more effective after crossings were raised and speed humps were installed on approaches (Gitelman et al. 2017). SFMTA implemented its first âhome zoneâ program near Marshall Elementary School (referred to as the âMinna-Natoma Home Zone Pilot Programâ) (SFMTA 2015). The program included the installation of traffic-calming measures in a two-by-two block radius around the Figure 2-14. Speed cushions (left) and chicanes and speed humps (right) in Seattle. (Source: Toole Design.)
Literature Review 29 school. The treatments included speed humps, edgelines, two raised crosswalks, curb extensions, and a road diet for one street. On average, motor vehicle speeds decreased to below 20 mph throughout the project area. The prevailing speeds on Minna and Natoma alleys, previously over 20 mph, decreased to below the 15-mph speed limit. Capp Street speeds reduced by 9 mph (from 26 to 17 mph), and speeds reduced from 25 to 21 mph on 15th Street. In addition, the perception of pedestrian safety with regard to vehicle yielding/stopping improved and pedestrian volumes in the project area increased by an average of 20%. Enforcement Countermeasures. Enforcement frequently is used by cities to encourage compliance with posted speed limits and deter dangerous driving behaviors like speeding. Although enforcement efforts can be effective, they are often only effective while the enforce- ment is being conducted or when the presence of enforcement is anticipated. ASE is considered the most effective form of enforcement for reducing vehicle speeds (Goodwin et al. 2015). High- visibility enforcement campaigns may also be effective, but documentation of their effectiveness on improving pedestrian safety in particular is lacking, and existing documentation indicates that the safety benefits are not guaranteed (Goodwin et al. 2015). Automated Speed Enforcement ASE involves the use of a fixed or mobile camera to measure vehicle speeds and photograph vehicles that exceed the speed limit by a certain amount. The effectiveness of ASE is well docu- mented (Goodwin et al. 2015, Cunningham et al. 2008, Freedman et al. 2006, Hu and McCartt 2016). Most studies of this treatment measure its effect on crashes; however, some studies reviewed its effect on travel speed, most commonly top-end speedersâthose who travel at least 10 mph over the speed limit. ASE cameras have been successfully used in various environments, including residential and arterial streets and school zones. ASE cameras can be fixed (remain at a single location) or mobile (attached to vehicles for use in various parts of a community). For example, an analysis of 14 urban arterials in Charlotte, NC, revealed that ASE cameras significantly reduced the percentage of top-end speeders (Cunningham et al. 2008). Freedman et al. (2006) reviewed the impact of ASEs at five school zones in Portland, OR, finding that mean and 85th percentile speeds decreased by 5 mph, and the percentage of top-end speeders decreased by approximately 66%. Speed measurements at comparison sites indicated that the decreased speeds were limited to the areas with the cameras. More recently, the City of Portland deployed speed cameras at four locations as part of its Vision Zero efforts (Vision Zero Network 2018). A review of speed safety camera data from three Figure 2-15. Rainier Ave S before (left) and after (right) the street reconfiguration. (Source: Seattle Department of Transportation.)
30 Pedestrian Safety Relative to Traffic-Speed Management locations indicated that the percentage of speeding and top-end speeding drivers decreased by 47% to 61% and 71% to 92%, respectively (Vision Zero Network 2018). The 85th percentile speeds decreased by 4 to 9 mph at all locations. Beginning in 2012, SDOT installed cameras in school zones where speeding had been identi- fied as an issue despite a 20-mph posted speed limit (SDOT 2017b; see Figure 2-16). The speed cameras operate only when the school zone flashing beacons are active, and by the end of 2015, the program had expanded to a total of 14 speed photo enforcement cameras. Since installa- tion, average speeds have decreased by 4%, and total crashes and pedestrian crashes have each decreased by 50%. New York City has also found success with this strategy. Using 3 years of before and after data for school zones within which NYCDOT installed speed cameras in 2014, the City found that the number of people injured in traffic declined by over 14% and the number of pedestrian injuries declined by 23% in the period after the cameras were activated (NYCDOT 2016; NYCDOT 2018). In particular, vehicleâpedestrian crashes declined by 23% after the cameras were installed. Seattle and New York City have also documented that drivers who receive a citation from the ASE cameras are unlikely to repeat the offense. In Seattle, 90% of people who received and paid for a speeding citation did not receive another citation (SDOT 2017b). In New York City, 81% of people who received a citation did not repeat the offense (NYCDOT 2016). Hu and McCartt (2016) measured the long-term impacts of ASE along 19 residential streets in Montgomery County, MD. About 7.5 years after the program began, speed cameras were associated with a 10% reduction in mean speeds and a 62% reduction in the likelihood that a vehicle was traveling more than 10 mph above the speed limit at camera sites. Mean speeds decreased by 13% from 2006 to 2014, compared to 5% and 4% at potential spillover sites and control sites, respectively. The percentage of vehicles exceeding the speed limit by more than 10 mph decreased by 64% compared to 39% and 43% at potential spillover sites and control Figure 2-16. Speed enforcement camera in school zone. (Source: Toole Design.)
Literature Review 31 sites, respectively. The results of the driver survey indicated that more than half (62%) supported the use of the speed cameras. The study findings indicate that the program was associated with spillover benefits, although additional research is needed to confirm the magnitude of the poten- tial spillover benefits due to lack of baseline speed data in those areas. Tang (2017) reviewed more than 10 studies of speed enforcement cameras conducted between 1997 and 2016 in the United States, Europe, and Australia and found that speed enforcement cameras effectively reduced vehicle speeds. Three European studies found that speed cameras were associated with reductions in average vehicle speeds ranging from 4 to 6 mph (Mountain et al. 2004; Gains et al. 2004 and 2005; Li et al. 2013 citing ARRB Group Project Team 2005). Looking at data from more than 3,000 sites with cameras, Tang (2017) and Li et al. (2013) found that the effectiveness of speed cameras is localized and does not spill over into other areas. Specifically, these authors found that the effects of the speed cameras were strongest close to the cameras and were limited to distances of up to 1,640 ft (500 m) from the cameras. Beyond 2,300 ft (700 m), the speed cameras had no effect. Li et al. (2015) used 8 years of crash and traffic count data and a beforeâafter Empirical Bayes methodology to measure the impact of ASE cameras in Edmonton, Canada. The results showed consistent reductions in different crash severities, ranging from 14% to 20%, with the highest reductions observed for severe collisions. Speed-related crashes reduced by nearly 19% (p < 0.05). The study also compared the effects of continuous and discontinu- ous enforcement strategies on different arterials and found that continuous enforcement was associated with a greater reduction in crashes of all types than discontinuous enforcement. The findings also suggest a spillover effect of enforcement on other approaches that are not experiencing enforcement. The Chicago DOT (2016) used crash data to analyze 107 locations related to 150 ASE cameras. Crash data from 2012 to 2013 were used to measure the âbeforeâ conditions, and data from 2014 to 2015 were used to measure the âafterâ conditions. The study included all crashes that occurred within 660 ft of a camera. The analysis revealed the following relevant findings comparing areas with ASE to the citywide average: â¢ Crashes involving bicyclists and pedestrians decreased by 17% compared to less than 1% citywide. â¢ Youth-related crashes decreased by 8% compared to a 4% increase citywide. â¢ Speed-related crashes increased by only about 2% compared to 20% citywide. In Europe and Australia, average speed enforcement as opposed to single-point enforcement is increasing in popularity. Most ASE programs in the United States measure vehicle speeds at a single location, whereas average speed enforcement (also called point-to-point enforcement) efforts use cameras placed at two ends of a specified road section to measure vehicle travel time between the two cameras. Soole et al. (2013) reviewed studies of average speed enforcement and found this approach is effective at reducing vehicle speeds, finding reported reductions of as much as 90% of the proportion of vehicles exceeding the speed limit. Soole et al.âs (2013) study also found little evidence to suggest that the benefits of speed enforcement spill over into areas outside of the immediate vicinity of the enforced area. This treatment often is used along higher- speed roads and highways and may therefore be applicable only in suburban or rural areas of the United States. This treatment may also be cost prohibitive to some jurisdictions in the United States where ASE is legal. Increasing numbers of cities are interested in the use of ASE because of its effectiveness, unbiased nature, and ability to mitigate disproportionate policing in certain neighborhoods. It is important to note that ASE programs and the placement of ASE cameras need to be
32 Pedestrian Safety Relative to Traffic-Speed Management implemented after a thorough review of the factors contributing to speeding (e.g., roadway design) in order to have the greatest chance of success. Additionally, partnership with his- torically disadvantaged communities is important to avoid exacerbating community conflicts, particularly in areas that tend to be surrounded by higher-speed roadways. High-Visibility Enforcement High-visibility enforcement campaigns are targeted enforcement efforts that are highly publicized to the general public. This treatment has been found to be effective in detecting alcohol-impaired driving and seatbelt use; however, existing evidence is mixed regarding its effectiveness with speeding, and some studies have found the impacts to be minimal (Walter et al. 2011 and Goodwin et al. 2015). In addition, the benefits of high-visibility enforcement programs are typically short-term and may not persist beyond the length of the campaign. A study of a high-visibility enforcement campaign along a 6-mi corridor in London reported decreases in 85th percentile speeds of less than 2 mph during the campaign and less than 1.5 mph up to 2 weeks after the campaign, relative to baseline speeds (Walter et al. 2011). The inconsistent and infrequent use of high-visibility enforcement programs by local municipalities further hinders the success and knowledge of the effectiveness of these types of programs (NTSB 2017). Successful enforcement campaigns typically combine enforcement campaigns with other treatments. See the Engineering Countermeasure Combinations section for examples of successful enforcement campaigns used in conjunction with other treatments. 2.2.4 Education and Marketing Countermeasures There is little literature about the effectiveness of educational efforts alone to reduce traffic speed and improve pedestrian safety. There were no academic studies on the topic, and most examples found were part of Vision Zero efforts to encourage drivers to slow down through marketing. Outreach efforts associated with Vision Zero and reducing traffic speed include yard signs, bumper stickers, commercials, and billboards (see, e.g., Figure 2-17). These treatments may serve to raise awareness about the campaign; however, their effectiveness at reducing driver speeds remains difficult to detect, in large part because they are often part of a comprehensive program. In the future, Vision Zero campaigns may serve as case studies to shed light on the impacts of educational campaigns on vehicle speed. Figure 2-17. Vision Zero public education materials from Seattle (left) and Portland (right). [Source: Seattle DOT (left) and Portland Bureau of Transportation (right).]
Literature Review 33 2.2.5 Policies, Programs, and Legislative Efforts Jurisdictions can implement various policies and programs to reduce vehicle speeds and increase pedestrian safety. Each of the strategies listed below will be briefly discussed in this section. Since there are few academic studies on these topics, refer to the information summa- rized from the interviews (Chapter 3) for more information about the following topics: â¢ Speed-limit reduction, â¢ Automated enforcement legislation, and â¢ Traffic-calming programs. Although Vision Zero programs are often adopted via policy, the programs themselves are so necessarily multifaceted that they will be covered under Comprehensive Programs in Section 2.2.7. Speed-Limit Reduction Posting speed limit signs and reducing speed limits are common tactics to encourage safe traffic speeds. However, reducing speed limits and posting new signs alone has not been found to be very effective at reducing vehicle speeds, especially when compared to the other counter- measures discussed in this chapter. Typically, for every 5-mph reduction in the speed limit, only a 1 to 2 mph reduction in average travel speeds is expected (Leaf and Preusser 1999). While a pedestrianâs risk of experiencing a severe or fatal injury when struck by a vehicle is greater at higher speeds, severe and fatal injuries still occur on roads with speed limits below 25 to 35 mph (RosÃ©n and Sander 2009; Tefft 2013; and Kroyer 2015). Pedestrian volumes are also typically much higher along lower speed roads. As such, there is a growing movement to reduce speed limits along streets that tend to have higher volumes of pedestrians. For example, Portland and Seattle have decreased speed limits on residential streets from 25 to 20 mph. Both Jurewicz et al. (2016) and Kroyer (2015) suggest that lowering traffic speeds to 15 to 20 mph is a logical component of a larger strategy for jurisdictions striving to improve pedestrian safety. Slower Speed Zones. School zones are areas that are near schools and these zones are often created with a unique set of policies, such as lower speed limits. In some jurisdictions, school zone speed limits are as low as 15 mph; however, this is not common practice (ITE n.d.). As discussed above, the implementation of countermeasures to reduce speeds has been found effective in school zones; these areas often serve as case studies for measuring countermeasure effectiveness, in part because communities are often more willing to experiment with more aggressive treatments in limited areas and when children are involved. In addition to school zones, cities all over the world have implemented programs to reduce speeds in designated areas to improve safety. These areas, sometimes referred to as âslow zone,â are growing in popularity in some cities in the United States due to the success of the program in London (Grundy et al. 2009, Li and Graham 2016). The exact design of each of Londonâs slow zones varies, but they typically include signs at the entrances and exits and engineering treat- ments such as speed humps, chicanes, and raised crossings, placed every 110 yards (100 meters). Grundy et al. (2009) and Li and Graham (2016) found that Londonâs program was associated with a 32% and 24% reduction in pedestrian fatalities, respectively. Using 20 years of crash data, Grundy et al. (2009) also found that the number of fatal or seriously injured children reduced by 50% and fatalities did not migrate to areas adjacent to the slow zones. In fact, areas adjacent to the slow zones were associated with an 8% reduction in fatalities. As part of the Cityâs Vision Zero efforts, New York City implemented a neighborhood slow- zone program in 2014. The neighborhood slow zones reduced the speed limit from 25 to 20 mph in a designated area and added pavement markings, signs, and speed humps to help encourage
34 Pedestrian Safety Relative to Traffic-Speed Management slower speeds. After comparing beforeâafter data at neighborhood slow zones and control sites, Hagen (2018) found that the neighborhood slow zones did not reduce vulnerable-user fatalities. Note that Hagen used only 2 years of postinstallation crash data and was unable to account for differences in pedestrian or vehicle volumes. Hagen also examined only differences in fatalities; it is possible New York Cityâs program did have an impact on pedestrian injury severity or the number of vehicleâpedestrian conflicts. Hagen (2018) also compared results from New York City and London, finding that Londonâs programs were strongly influenced by the use of a greater number and diversity of engineering treatments. New York City uses only speed humps, whereas London uses 12 types of physical treatments, including speed humps, speed cushions, raised crosswalks, curb extensions, and pedestrian refuge islands. In addition, London installed approximately 16 traffic-calming devices per mile, whereas New York City installed three devices per mile of slow-zone street. The Netherlands has been implementing slow zonesâareas with a posted speed of slightly less than 20 mph (30 km/h)âin residential areas since the 1990s. From 1997 to 2002, the percent- age of urban residential streets with 30 km/h (19 mph) speed limits increased from 15% to 50% (SWOV 2009). A beforeâafter analysis of crash and injury data indicated that the fatality rate per 1,000 km of road length decreased by 10% and the in-patient (patients who were admitted to the hospital and stayed at least 12 h; not necessarily âsevereâ) rate decreased by 60% (Wegman et al. 2005, see Figure 2-18). The residential streets in the Netherlands generally have a fatality and in-patient rate of 0.324 per million vehicle-km. Based on the length of residential streets included in the 30 km/h (19 mph) zone, 948 fatality and in-patients were expected in 2002, however, only 294 victims were recorded. The number of lives saved by the program in 2002 is estimated to be 654. Shared streets, such as the Dutch and British concepts of âWoonerfsâ and âHome Zones,â combine low speed limits with a strong emphasis on pedestrian safety and the creation of out- door areas that are safe for children. These design strategies are radically different from most streets in the United States and create spaces that do not clearly delineate spaces for different road users, such as vehicles and pedestrians; instead, the roadway is shared. On shared streets, vehicles are typically encouraged to travel at 10 to 15 mph. A review of 39 home zones in London found that vehicle operating speeds decreased by 10 to 15 mph at more than half of the designs surveyed (Gill 2007). Wargo and Garrick (2016) reviewed the impact of six shared street intersection designs in the United States and abroad and found that vehicle speeds ranged from 5 to 10 mph. The authors also found that the intersections that were âmore sharedâ (i.e., higher vehicle and pedestrian volumes) were associated with lower vehicle speeds. Figure 2-18. Fatalities and in-patients in the Netherlands from 1992 to 2002. (Source: Wegman et al. 2005.)
Literature Review 35 Systemic Approaches to Reducing Speed Limits. In addition to reducing speeds in designated areas, some jurisdictions are taking a citywide approach by setting new speed limits based on roadway function or class. Some cities, including Seattle, Portland, and New York City, have reduced speeds on local streets after obtaining local authority from state legislation [Ferrier 2017; SDOT 2017b; Portland Bureau of Transportation (PBOT) 2018a; City of Boston 2016]. Seattle and New York City lowered the default speed on arterial streets from 30 to 25 mph. Seattle and Portland recently reduced the speed limit on residential streets from 25 to 20 mph (SDOT 2017b; PBOT 2018a). Another approach some cities are pursuing is to change the process and metrics that are used to set speed limits to better reflect community goals associated with safety and mobility. Since the 1940s, speed limits have been predominantly set using the 85th percentile speedâthe speed at or below which 85% of vehicles are traveling (TRB 1998, FHWA 2012a). Use of the 85th percentile speed assumes that most drivers are traveling at an appropriate speed given weather, geometry, and roadside conditions. Growing evidence suggests this approach may no longer be appropriate or equate to safe driving speeds (NTSB 2017; Forbes et al. 2012). As Donnell et al. (2009) suggest, using the 85th percentile speed to set speed limits may lead to a cycle of ever-increasing speed limits and reduced safety. The process outlined in the MUTCD emphasizes the use of 85th percentile speeds and advises that speed limits, even in special speed zones, be within 5 mph of the 85th percentile speed. The FHWAâs USLIMITS2 (2012b) is a software system that can be used to set speed limits on all road types; it was developed to help communities develop safe, rational speed limits that protect the public. USLIMITS2 responds to a widespread need for rational guidance on how to integrate roadway characteristics beyond the 85th percentile speed into speed limits (Srinivasan et al. 2006). The system allows users to enter roadway information into the program, which then presents a recommended speed limit; the program allows users to integrate a variety of metrics beyond the 85th percentile speed, including crash history, 50th percentile speed, and pedestrian and bicyclist volumes. It is unclear how many jurisdictions currently use USLIMITS2 or how effective it is as a tool to develop slower speed limits. There is a growing movement among practitioners to modify the MUTCD and encourage local jurisdictions to deemphasize the 85th percentile speed and follow a Safe System approach (see Chapter 1) (NTSB 2017). NTSB (2017) advises that FHWA revise Section 2B of the MUTCD so that the consideration of roadway characteristics beyond the 85th percentile speed, including pedestrian activity, is required in all engineering studies relating to setting speed limits. In addi- tion, NTSB (2017) recommends the removal of the current MUTCD guidance that states that speed limits in speed zones should be within 5 mph of the 85th percentile speed. To date, there are not many other examples of widespread approaches to setting speed limits, but a few cities are experimenting with new methods. The City of Portland does not use the 85th percentile speed to set speed limits; instead, the City emphasizes the use of injury crashes and the amount of physical separation between motor vehicles and vulnerable road users to determine safe speed limits (PBOT 2018b). The City of Seattle plans to evaluate existing speed limits along 20 major arterials with a high vehicleâpedestrian crash history. As part of its speed limit evaluation, the City will consider the 85th percentile speed, 50th percentile speed, crash history, and whether the location is associated with crashes that list speeding as a contributing factor (SDOT 2017b; Le 2018). Automated Enforcement Legislation As discussed in Section 2.2.3, research indicates that ASE is the most effective form of enforce- ment (Goodwin et al. 2015). However, in some jurisdictions, automated enforcement practices, or the act of issuing citations using the cameras, is illegal. To date, 143 communities have speed
36 Pedestrian Safety Relative to Traffic-Speed Management camera programs (Insurance Institute for Highway Safety 2018), although only 16 states and the District of Columbia allow them (see Figure 2-19). Other communities are experimenting with ways to use technology to slow speeds even within the confines of rigorous privacy laws (see example in Chapter 3). Traffic-Calming Programs Formal traffic-calming programs exist in many cities across the country. These programs help local planners and engineers implement traffic-calming projects, and in some cases, provide a clear process for local residents to submit requests for traffic-calming projects. Some programs have criteria that limit the implementation of traffic-calming projects to areas proven to be unsafe, either through speed studies or crash analyses. These programs have proven to be effec- tive at reducing speeds on individual streets and typically result in the installation of many of the engineering treatments discussed above (City of Cambridge 2012; City of Alexandria n.d.). Speed humps and lumps are the most effective countermeasures to reduce speeds and tend to be common treatments installed as part of traffic-calming programs. 2.2.6 Comprehensive Programs This section includes a review of documented projects that included a combination of engi- neering and other types of treatments (e.g., policy, enforcement, education) to reduce vehicle Figure 2-19. U.S. states in which automated enforcement is legal (as of June 2018). (Data source: Insurance Institute for Highway Safety; Image source: Toole Design.)
Literature Review 37 speeds and improve pedestrian safety. Although most of the evaluations discussed did not measure changes in vehicleâpedestrian crashes, the notable reductions in vehicle speeds indi- cate that these programs can improve pedestrian safety by reducing the likelihood of a crash in the first place and the likelihood of a severe injury in the event that a pedestrian is struck by a vehicle. Retting et al. (2008) conducted a study of mobile and fixed ASE cameras in Montgomery County, MD, and found that the percentage of drivers traveling at least 10 mph over the speed limit decreased by 70% on streets with warning signs and cameras, 39% at locations with only warning signs, and 16% on residential streets without any treatment. The treatments occurred in conjunction with an extensive public awareness campaign and a 30-day warning period. The authors suggest that the large decreases in top-end speeding vehicles throughout the study area suggest that the benefits of cameras may not be limited to the streets with cameras. It is likely that the geographic reach of camera-related benefits is related to the use of mobile cameras (as opposed to only fixed cameras) and the extensive public outreach campaign. However, addi- tional research is needed to confirm this hypothesis. Vision Zero Vision Zero is a strategy to eliminate all traffic-related fatal and serious injuries (Vision Zero Network n.d.; see sidebar). Although originally a Swedish concept, Vision Zero has become popular in the United States as a way to pursue safety through a Safe System approach, which means it seeks to address the root causes of traffic fatalities and severe injuries systemically, rather than through spot fixes. Vision Zero strategies focus on the protection of all road users, with specific emphasis on vulnerable road users. In fact, many municipalities adopt Vision Zero strategies specifically because of the vulnerability of pedestrians (NTSB 2017). What Is Vision Zero? Vision Zero is a transportation safety philosophy that was developed in Sweden in the late 1990s to eliminate traffic deaths and serious injuries in the transportation system. Vision Zero calls on communities to think differently about traffic safety and commit to the idea that people should not be killed or experience life-changing injuries because of simply using our streets. Vision Zero recognizes that people make mistakes, and that the transportation system should be designed to minimize the impacts of those errors. When the system is designed with this mindset, crashes that do occur will be less severe, with the aim that death and life-changing injuries are prevented. Per the Vision Zero Network, four actionable strategies are recommended for Vision Zero efforts: 1. Prioritize roadway design. 2. Focus on speed management. 3. Use impactful education strategies. 4. Ensure enforcement is equitable. (Source: Vision Zero Network.)
38 Pedestrian Safety Relative to Traffic-Speed Management Two key elements of Vision Zero and other Safe System approaches are the understanding of the human bodyâs vulnerability and the fact that people, no matter how well intentioned, make mistakes. Based on this understanding, a Safe System approach to roadway safety seeks to minimize opportunities for human error that could lead to fatalities and severe injuries. A primary implication of Vision Zero and Safe System approaches is the need to reduce traffic speeds in order to reduce the severity of traffic-related injuries (Fleisher et al. 2016). As such, speed management is a key component of nearly every Vision Zero action plan. Fleisher et al. (2016) developed a list of Vision Zero best practices by reviewing the actions and countermea- sures included in Vision Zero strategies from eight U.S. cities and Sweden, the Netherlands, and London. Efforts to reduce vehicle speeds were included in every jurisdictionâs strategy, and spe- cifically mentioned as part of engineering, education, enforcement, policy, and monitoring and evaluation efforts in nearly all plans. Notably, the use of intelligent speed adaptation technolo- gies was listed as a best practice among all of the international strategies, but none in the United States. Table 2-2 presents examples of the speed-related actions from a variety of Vision Zero action plans. The majority of speed-related action items listed in Vision Zero action plans are engineering strategies, with enforcement strategies as the next most common category. The Vision Zero Difference. The individual countermeasures implemented by Vision Zero jurisdictions do not differ from those discussed earlier in the chapter; however, the combination of countermeasures implemented as part of a Vision Zero strategy coupled with the emphasis on a holistic approach and political support generated by these campaigns makes it a comprehensive approach unlike any other. Following is a list of key elements that contribute to Vision Zeroâs comprehensive approach. The information comes from a review of Vision Zero action plans from some of the nationâs leading Vision Zero municipalities, including Seattle (City of Seattle 2015); Portland (City of Portland 2016); Denver (City and County of Denver 2017); New York City (City of New York 2014); Washington, D.C. (District of Columbia 2015); Chicago (City of Chicago 2017), Austin (City of Austin 2016); and Los Angeles (City of Los Angeles 2015). As reflected in these plans, Vision Zero efforts â¢ Require leadership and commitment from local political leaders and city transportation staff. â¢ Generate public support and typically include extensive public engagement efforts. â¢ Require the collaboration of multiple public and private entities, many of whom may not otherwise collaborate. â¢ Follow a data-driven approach that promotes the prioritization and implementation of effective countermeasures to address the leading causes of fatal and serious injuries. â¢ Often take an aggressive approach to reducing speeds through education and media campaigns, enforcement, engineering, and policy-related countermeasures. â¢ Become members of an international network that promotes the sharing of best practices to improve roadway safety. â¢ Use evidence and support generated through the effort to reduce speed limits on local roads. â¢ Provide evidence for other major cities to reduce speed limits on local roads. â¢ Consider equity impacts when determining where and how to implement countermeasures so that they do not exacerbate existing social injustices and health disparities. In addition, the data-driven approach of Vision Zero provides cities with opportunities to track progress and build momentum. Vision Zero plans are often long-range, but include monitoring plans to report progress to members of the public on an annual basis. Several Vision Zero plans, including those from the City and County of San Francisco (2017), Austin (2016), Portland (2016), and Philadelphia (2017), include specific performance metrics that cities will track on an ongoing basis. Many Vision Zero programs include the development of a high-crash or high-injury network, which cities use to prioritize the locations and types of countermeasures that are implemented.
Action Type of Action Vision Zero Action Plan Create 25 new arterial slow zones. Engineering New York City (2014) Implement eight new neighborhood slow zones. Engineering New York City (2014) Install 250 speed bumps, including in neighborhood slow zones. Engineering New York City (2014) Install traffic signals where needed for speed control via coordinated arterial signal time. Engineering New York City (2014) Lower speed limits on 12 identified corridors in 2015. Engineering Seattle (2015) Update 100% of the expired speed surveys on the priority corridors by the end of 2017. Engineering Los Angeles (2015) Install speed safety zones around schools. Engineering Los Angeles (2015) Improve street design to support safe speeds in conjunction with posted speed reduction on four to six streets annually in the High-Crash Network, prioritizing improvements in and engaging with Communities of Concern. Engineering Portland (2016) Increase speeding enforcement at the precinct level. Enforcement New York City (2014) Install speed cameras at 20 new authorized locations. Enforcement New York City (2014) In 2015, install at least 12 new cameras in six school zones to reduce speeds and improve safety for kids. Enforcement Seattle (2015) Create 15 mph âSafe Zonesâ around schools, parks, and high concentrations of seniors or youth to apply slower speed limits for expanded hours. Support with automated enforcement. Enforcement Washington, D.C. (2015) Undertake a high-quality ad campaign aimed at reducing speeding, failure-to-yield, and other forms of reckless driving. Education New York City (2014) Invest at least $2 million toward a comprehensive education campaign that addresses top collision factors, such as speeding and insobriety. Education Los Angeles (2015) Support bills in the state legislature to reduce the citywide default speed limit to 25 mph. Policy Boston (2016) Work with State Legislators to gain State approval for speed cameras along Roosevelt Boulevard as a pilot program. Policy Philadelphia (2017) Work at the local and state levels to lower default speed limits congruent with research on speed and best practices. Policy Austin (2016) (Source: Toole Design, 2018.) Table 2-2. Selection of speed-related actions from various Vision Zero action plans.
40 Pedestrian Safety Relative to Traffic-Speed Management Achieving Vision Zero. Only a few cities have been pursuing Vision Zero long enough to have data to evaluate their efforts; of those, demonstrable reductions in pedestrian crashes have been documented in New York City and San Francisco. New York City is one of the most success- ful examples of the potential impact of Vision Zero; this may be because it was one of the first cities to adopt a Vision Zero action plan and has already implemented many the planâs actions (City of New York 2018). The city has seen a noticeable reduction in traffic-related fatalities since Vision Zero was adopted [see Figure 2-20 New York City traffic fatalities before and after the Vision Zero policy was adopted (City of New York 2018)]. Most notably, the 4-year average in pedestrian fatalities decreased from 158 fatalities before Vision Zero was adopted to 132 fatalities (a 16% drop; City of New York 2018). In San Francisco, from one year before Vision Zero was initiated to 2016, pedestrian fatalities decreased from 21 to 16 (Vision Zero SF 2017). The evidence is promising, but given the pro- pensity of pedestrian crashes to vary from year to year and to be affected by several factors that are not directly or at all within the citiesâ control (e.g., the economy and its effects on the num- ber of drivers; see Greedipally et al. 2018), many Vision Zero cities are cautious about drawing conclusions without more data. As more data become available in the coming years, the trends will become more apparent and should provide keener insight into the effectiveness of various strategies in different contexts. 2.2.7 Summary of Findings Existing research on the effectiveness of countermeasures to reduce traffic speeds and increase pedestrian safety indicates a few key trends. First, treatments with vertical deflection, such as 381 394 387 364 297 321 324 275 289 260 273 249 278 299 258 234 230 214 0 50 100 150 200 250 300 350 400 450 500 Tr affi c Fa ta liti es Year NYC Traffic Fatalities 2000â2017 Before Vision Zero After Vision Zero 2000â2013 average prior to Vision Zero 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07 20 08 20 09 20 10 20 11 20 12 20 13 20 14 20 15 20 16 20 17 Figure 2-20. New York City traffic fatalities in the years before and after the Vision Zero policy was adopted. (Data source: NYCDOT and NYPD; Image source: Toole Design.)
Literature Review 41 speed humps and speed tables, are generally considered the most effective. These are followed by treatments with horizontal deflection, such as chicanes and traffic circles. Both types of deflec- tion are considered more effective than enforcement. When enforcement is used, ASE is considered the most effective and can help mitigate con- cerns about disproportionate policing in certain neighborhoods. However, even ASE needs to be implemented carefully and in partnership with historically disadvantaged communities to avoid exacerbation of community tensions. A thorough understanding of the factors that contribute to speeding issues will give communities the greatest chance of success with an ASE program. Table 2-3 presents a summary of the findings discussed in this chapter. In general, engineering and enforcement efforts are both more effective than reducing speed limits alone; speed-limit reduction alone was the least effective treatment reviewed. Refer to Appendix A for additional information on the studies reviewed. Few studies evaluate the effectiveness of comprehensive programs that use a variety of countermeasures to reduce speeding; however, existing evidence indicates that these compre- hensive approaches are effective. Cities have successfully reduced vehicle speeds in specific areas when implementing a variety of treatments, such as speed humps and chicanes, neck downs, or curb extensions; raised crossings and speed humps; lane reductions and pedestrian crossing enhancements; and engineering treatments combined with education and temporarily increased enforcement. It is hoped that as more Vision Zero efforts have been in place for a longer time, additional studies on the effectiveness of comprehensive programs will emerge. The extent to which the safety benefits of countermeasures that reduce traffic speeds spill over into other areas remains unclear. Some studies have found that reduced travel speeds are limited to areas immediately adjacent to treatments, whereas other studies have indicated that reduced speeds have been observed on nearby streets that did not receive treatments. Addi- tional research on this topic would benefit the field. These and other future research needs are covered in Chapter 4.
Countermeasure Type Effectivenessa Roadway Context Safety Benefit Referencesb Notes Speed humps Engineering (vertical deflection) Proven Local/low-speed collectors CMF for vehicle- pedestrian crashes: 0.45 to 0.74 Ewing 1999; Tester et al. 2004; Mountain et al. 2005; Ponnaluri and Groce 2005; Chen et al 2013; FHWA 2014; Rothman et al. 2015; Agerholm et al. 2017 Also proven to be effective when used with raised crossings or neck downs Speed lumps and speed cushions Engineering (vertical deflection) Proven Local/low-speed collectors Reduces 85th percentile and mean speeds City of Alexandria n.d.; Gulden and Ewing 2009; FHWA 2014 Similar effectiveness to speed humps and better suited for emergency- response vehicles Speed tables and raised crossings Engineering (vertical deflection) Proven Local/low-speed collectors and special zones like school zones CMF for vehicleâ pedestrian crashes: 0.55 Huang and Cynecki 2001; FHWA 2014 Also proven to be effective when used with speed humps Chicanes Engineering (horizontal deflection) Proven Local/low-speed collectors Reduces 85th percentile and mean speeds Ewing 1999; FHWA 2014; Agerholm et al. 2017 â Raised medians and pedestrian crossing islands Engineering (horizontal deflection) Proven Arterials/higher- speed roads and special zones like school zones Reduces 85th percentile and mean speeds Ewing 1999; NYCDOT 2004; FHWA 2014 Proven to be more effective when used with neck downs Mini traffic circles Engineering (horizontal deflection) Proven Local/low-speed collectors Reduces 85th percentile speeds Ewing 1999; FHWA 2010; Zegeer et al. 2013; FHWA 2014; City of Seattle 2015; â Street reconfigurations and road diets Engineering Proven Arterials/higher-speed roads Reduces 85th percentile speeds, top-end speeders, and pedestrian crashes Corkle et al. 2001; Knapp and Giese 2001; Chen et al. 2013; Thomas 2013; FHWA 2014; SDOT (2010, 2011, 2013, 2015, 2017a, 2017b) â Speed feedback signs Education Proven Arterials/higher- speed roads and special zones like school zones Reduces 85th percentile and mean speeds Ullman and Rose 2005; Hallmark et al.2013; FHWA 2014 â Speed-activated speed-limit signs Education Proven Arterials/higher-speed roads Reduces 85th percentile speeds Hallmark et al. 2013; FHWA 2014 â ASE Enforcement Proven Varies by jurisdiction, typically special zones like school zones or arterials/higher- speed roads Reduces vehicleâ pedestrian crashes, 85th percentile and mean speeds, top- end speeders Freedman et al. 2006; Cunningham et al. 2001; Retting et al. 2008; Goodwin et al. 2015; Li et al. 2015; Hu and McCartt 2016; NYCDOT 2016; SDOT 2017b; Portland Bureau of Transportation 2018a and 2018b â Table 2-3. Summary of speed management and safety outcomes for each countermeasure.
Curb radius reduction Engineering Promising Arterials/higher-speed roads May reduce speeds Thomas et al. 2016 â Speed-limit reduction Policy Promising All May reduce injury severity and mean speeds Leaf and Preusser 1999; RosÃ©n and Sander 2009; Tefft 2013 Potentially low effectiveness when used alone; better complemented by physical design changes Neckdowns/ bulb-outs/ curb extensions/ chokers Engineering (horizontal deflection) Promising Local/low-speed collectors and special zones like school zones May reduce 85th percentile and mean speeds Ewing 1999; King 1999; Corkle et al. 2001; FHWA 2014; Bella and Silvestri 2015; Proven to be more effective when used with medians and crosswalks. May be less effective at intersections In-street pedestrian- crossing signs (MUTCD R1-6) Engineering Promising Local/low-speed collectors May reduce mean speeds Kamyab et al. 2003; Kannel et al. 2003; Gedafa et al. 2014; Van Houten and Hochmuth 2017 â High-visibility enforcement Enforcement Promising Arterials/higher-speed roads May reduce 85th percentile speeds Retting et al. 2008; Walter et al. 2011; Goodwin et al. 2015 â Vision Zero policy* Policy Promising All May reduce vehicleâ pedestrian crashes and vehicle speeds City of New York 2018; City and County of San Francisco 2017 â Lane narrowing with pavement markings Engineering Unknown All May reduce 85th percentile and mean speeds VHB 2008; FHWA 2014; Thomas et al. 2016 â Education and marketing Education Unknown All May reduce speeds Blomberg and Cleven 2006; SFMTA 2015 The effects of this treatment alone have not been studied. It is typically used in combination with other treatments. a Definitions for Effectiveness: âProvenâ countermeasures include those that are proven in literature to be effective based on several evaluations with consistent results. âPromisingâ countermeasures include those with limited evidence, but which are believed to be effective based on traffic engineering principles or other best practices. âUnknownâ countermeasures are those with inconsistent or inconclusive outcomes, but which may be effective in some circumstances. b For additional information, see Appendix A. *Vision Zero, as a comprehensive effort, is much more than a single countermeasure; however, it is listed in this table as a policy option because adopting it as policy can be an effective and important step toward catalyzing or continuing effort s to improve pedestrian safety. â = N/A.