Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (2008)

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68 A P P E N D I X B Case Studies

The site of this case study was the intersection of Whiskey Hill Road and Meridian Road in Clackamas County, Oregon. B1.1 Pre-Screening Clackamas County identified this intersection because of speed and safety concerns. In particular • Meridian Road: Complaints were made regarding people running the northbound stop sign. • Whiskey Hill Road: Horizontal curves, grade, and limited sight distance made it difficult to anticipate the upcoming intersection. • Special condition: There is a school adjacent to intersection, which motorists also had difficulty anticipating. Note: Crosswalks near the school make this location especially sensitive to speed. B1.1.1 Intersection Characteristics B1.1.1.1 Traffic Volumes There is approximately 2,100 average daily traffic (ADT) during a typical weekday on Whiskey Hill Road. There is approximately 1,300 ADT during a typical weekday on Meridian Road. Note: Low volume provided an opportunity for drivers to travel at free-flow speeds. B1.1.1.2 Traffic Composition There is a high percentage of agricultural truck traffic and school buses traveling through the area. B1.1.1.3 Intersection Features This is a two-way, stop-controlled intersection, with stop signs on the north and south approaches of Meridian Road. Whiskey Hill and Meridian roads are two-lane roadways. The west approach of Whiskey Hill Road features a horizontal curve, sight distance issues, and grade changes. B1.1.1.4 Speed Data Speed is defined according to the “basic rule.” 69 A P P E N D I X B 1 Whiskey Hill Road/Meridian Road

Note: Basic Rule is, “No person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing.” A speed study conducted in August 2005 found Whiskey Hill Road • 85th-percentile speed = 48.7 mph • Percent exceeding 45 mph = 28% Meridian Road • 85th-percentile speed = 56.2 mph • Percent exceeding 45 mph = 66% Note: Clackamas County staff said speeds in this area were not extremely high, but drivers were traveling faster than desired. They also reported multiple complaints of drivers running the stop sign northbound on Meridian Road. This may have been caused by drivers’ inability to adapt to the intersection influence area and having insufficient distance to stop. In addition, staff from the adjacent school had received complaints of vehicles driving too fast. There are 25 mph school zones on the north approach of Meridian Road and the east approach of Whiskey Hill Road. B1.1.1.5 Crash Records One crash was reported in 2004 and involved a vehicle running the stop sign. B1.1.1.6 Environment The surrounding area is rural. An elementary school is located on the northeast corner of the intersection. Lenhardt Airport is located north of the elementary school on Meridian Road. A convenience store is located on the intersection’s southeast corner. Single-family residences are situated adjacent to, and east of, Meridian Road and south of Whiskey Hill Road. B1.2.1 Assess Data Is speed the primary issue? Are speed reduction treatments needed? • No speed limit is posted; therefore, the basic rule applies. • Given the residential driveways and school zone on Meridian Road, and the horizontal cur- vature, grade changes, and limited sight distance on Whiskey Hill Road, 45 mph is a reason- able speed for these roadways. • Based on the speed data for Meridian Road and Whiskey Hill Road, approximately 66% and 28% of drivers exceeded 45 mph, respectively. Note: Based on discussions with the county, a speed of 45 mph was reasonable for each inter- section approach. On which approaches is speed reduction needed? • Based on crash data and public complaints, there was a need to reduce speeds in the north- bound direction on Meridian Road to eliminate stop sign violations. 70 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections

• Based on complex roadway geometry and limited sight distance, there was a need to reduce speeds in the eastbound direction of Whiskey Hill Road prior to the intersection and school. Note: The school is more visible to approaching drivers traveling in the southbound and westbound directions. Therefore, no speed reduction treatments are needed on those approaches. B1.2 Treatment Screening Potential treatments are • Reduced lane width, • Visible shoulder treatments, • Speed tables, • Rumble strips, • Roadway environment, • Approach curvature, • Roundabouts, • Splitter islands, • Longitudinal pavement markings, • Transverse pavement markings, and • Dynamic warning sign. B1.2.1 Fatal Flaws Note: Clackamas County was interested in a treatment that would be implemented quickly and easily. However, the county had limited funding available for the treatment project. Reduced Lane Width—Existing lane width is 11 ft. Visible Shoulder Treatment—Existing study roadways have no shoulders. Exhibit B1-1 illustrates the limited shoulder and narrow cross section on Meridian and Whiskey Hill Roads. Speed Tables—The 85th-percentile speeds are greater than 45 mph. Therefore, speed tables were not appropriate for these high-speed study roadways. Rumble Strips—Clackamas County was not interested in installing rumble strips at this loca- tion due to potential noise impacts on nearby residences and the school. Figure B1-2 illustrates the residences near Whiskey Hill and Meridian Roads. Roadway Environment—Existing vegetation and a continuous drainage ditch adjacent to the roadway made it difficult to install effective roadway environment treatments such as landscaping. Exhibit B1-3 illustrates the existing roadway vegetation on Meridian and Whiskey Hill Roads. Approach Curvature—Existing roadways have a narrow cross section and right-of-way is constrained. Roundabout—Clackamas County did not have funding available to consider a roundabout as a potential intersection treatment. In addition, existing roadways have narrow cross sections and right-of-way is constrained. Splitter Island—Existing roadways have narrow cross sections and right-of-way is constrained. Case Studies: Whiskey Hill Road/Meridian Road 71

Dynamic Warning Signs—Clackamas County did not have funding available to consider dynamic warning signs as a potential treatment. In addition, the rural location made it difficult and expensive to provide power to the signs. B1.2.2. Evaluate Potential Treatments After the research team identified the “fatal flaw” treatments that were not feasible to install at this intersection (reduced lane width, visible shoulder treatments, speed tables, rumble strips, roadway environment, approach curvature, roundabouts, splitter islands, and dynamic warning sign), two potential treatments remained: longitudinal and transverse pavement markings. At this point, the research team reviewed past research and evaluated each potential treatment to assess its effectiveness and determine which was the most appropriate. B1.2.2.1. Longitudinal Pavement Markings No research had been conducted to show this as an effective speed reduction treatment. Additionally • This treatment requires a large amount of pavement marking material, depending on the treatment boundary. • Longitudinal pavement markings may conflict with multiple adjacent driveways. • This solution may be more effective in areas with speed adaptation issues or a large number of elderly drivers. 72 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (a) Meridian Road (b) Whiskey Hill Road Exhibit B1-1. Shoulders and cross sections on Meridian and Whiskey Hill Roads.

B1.2.2.2. Transverse Pavement Markings Past research has shown this treatment to be effective at reducing speeds. In addition to review- ing past research and treatment information, the research team also reviewed the objectives for the speed reduction, including the target speed and locations where speed reduction was desired. How much speed reduction is desired? • Eastbound direction: 45 mph is a safe speed to maneuver the curves and grade. • Northbound direction: 45 mph at stopping sight distance (SSD) was recommended to reduce speeds at the intersection’s approach and throughout the school zone. Where should speed be reduced? Speed reduction was needed at the eastbound and northbound intersection approaches, beginning approximately 500 ft SSD from the intersection. B1.3 Selecting Treatments B1.3.1 Implementation—Treatment Layout Based on the review of treatment information and the objectives for reducing speeds, the research team selected transverse pavement markings for this site. Case Studies: Whiskey Hill Road/Meridian Road 73 Exhibit B1-2. Residences near Whiskey Hill and Meridian Roads.

Exhibit B1-4 illustrates a schematic of the proposed treatment layouts at the Whiskey Hill Road/Meridian Road intersection. Meridian Road (south approach) • Treatment Location 1: School Ahead sign at mile post 4.12, • SSD at 55 mph is also near mile post 4.12 (approximately 500 ft from the intersection), and • Treatment Location 2: 400 ft downstream of the School Ahead sign and after the existing driveways on Meridian Road. Whiskey Hill Road (west approach) • Treatment Location 1: Intersection Ahead sign at mile post 1.41, • Treatment Location 2: Approximate point of curvature at mile post 1.47, and • The installation points closest to the intersection (mile posts 4.12 and 1.41) were chosen because of the existing signs at those locations and because the signs are near the SSD for 55 mph (495 ft, Exhibit 3-1 in the “Green Book” [AASHTO, 2004]). The existing signs cur- rently serve to alert drivers of the upcoming intersection. The markings have the potential to draw additional attention to those warning signs and encourage drivers to reduce their speeds as they approach the intersection. The installation points beyond the upstream treatments are located where the roadway envi- ronment changes, such as the approximate point of curvature (Whiskey Hill Road, mile post 1.47) or presence of driveways (Meridian Road, mile post 4.21). In addition, placing a treatment at the end of the tangent at the point of curvature on a roadway allowed drivers a consistent view of the treatment ahead. 74 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (a) Whiskey Hill Road (b) Meridian Road Exhibit B1-3. Existing roadway vegetation on Meridian and Whiskey Hill Roads.

Case Studies: Whiskey Hill Road/Meridian Road 75 Exhibit B1-4. Schematic of Whiskey Hill Road/Meridian Road intersection proposed treatment layouts.

B1.3.2 Treatment Design Options Full transverse bars • These are more noticeable to drivers and, therefore, potentially more effective at reducing speeds. • In some cases, there have been reports of motorcycles slipping on the markings while decelerating. Peripheral transverse bars • These require less maintenance than full transverse bars. • They are less expensive to install due to limited material. • They potentially create a narrowing effect of the travel way. Note: Clackamas County chose to install peripheral transverse bars due to the potential safety issues for motorcycles and the decreased need for maintenance. B1.3.3 Treatment Design—Peripheral Transverse Bars • The peripheral bars were designed to extend perpendicularly into the travel way from the edge and center lines, but did not extend into the wheel path of vehicles. • The design includes five pavement markings placed in a series. • They are spaced approximately 15 ft apart. • Each marking is approximately 12 to 24 in. in width and between 18 to 33 in. in length. • The length of each peripheral bar depends on the existing lane width and the width of the wheel base for vehicles that commonly travel through the area. Exhibit B1-5 illustrates the proposed peripheral transverse pavement marking design for the Whiskey Hill Road/Meridian Road intersection. Travel way width = 10’6” Typical wheel base = 8’6” Bar dimensions = 12” × 8” B1.3.4 Treatment Testing and Installation • April 2006—“Before” testing, • May 2006—Treatment installation, and • September 2006—“After” testing. Exhibits B1-6 and B1-7 illustrate the installed treatments at the Whiskey Hill Road/Meridian Road intersection. 76 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Exhibit B1-5. Peripheral transverse pavement marking design.

Case Studies: Whiskey Hill Road/Meridian Road 77 Exhibit B1-6. Northbound on Meridian Road near mile post 4.12. Exhibit B1-7. Eastbound on Whiskey Hill Road near mile post 1.41.

The site of this case study was the intersection of SR 20 and Marysville Road in Marysville, California. B2.1 Pre-Screening The California Department of Transportation (Caltrans) identified this intersection as having speed and safety issues. SR 20 and Marysville Road—Rear-end crashes resulted from high speeds through the intersection, and there was inadequate intersection visibility or awareness. B2.1.1 Intersection Characteristics B2.1.1.1 Traffic Volumes No traffic volume data was available for this site. B2.1.1.2 Traffic Composition The intersection accommodates commuter traffic traveling to and from Marysville and Yuba City. Note: A gas station at the intersection’s northeast corner creates a high number of pass-by trips turning off and on the highway. B2.1.1.3 Intersection Features This is a two-way and stop-controlled intersection, with a stop sign on Marysville Road. SR 20 and Marysville Road are two-lane roadways. An eastbound left-turn lane and westbound right-turn lane exist on SR 20. Note: The slight curvature and/or location of the stop sign may make it difficult for vehicles to see the upcoming T-intersection. Stop Ahead signing and pavement legends have been installed at the intersection approach. B2.1.1.4 Speed Data The posted speed is 55 mph on SR 20 and Marysville Road. A speed study conducted on SR 20 revealed critical speeds of 66 mph. Note: Commuter drivers are familiar with the area and may not feel the need to reduce speeds at the side-street intersections, such as Marysville Road. 78 A P P E N D I X B 2 SR 20/Marysville Road

B2.1.1.5 Crash Record Crash history indicates multiple rear-end crashes involving southbound vehicles on Marysville Road, and multiple broadside crashes involving eastbound and westbound vehicles on SR 20. Both crash types at this location have caused injuries. Note: The rear-end crashes on Marysville Road may be a result of inadequate visibility of the approaching intersection. Broadside crashes on SR 20 may be a result of vehicles not being aware of upstream vehicles slowing down to make turning movements at the intersection. B2.1.1.6 Environment The surrounding area is rural and open. A small commercial development exists at the intersection’s northeast corner. Note: Open fields are south of the intersection; therefore, the openness may create intersec- tion visibility issues and may provide a more comfortable environment for higher speeds. In addition, this could prevent drivers from identifying and changing speeds in the intersection influence area. B2.1.2 Assess Data Is speed the primary issue? Are speed reduction treatments needed? A speed study indicated vehicles were exceeding the speed limit by over 10 mph. Commuter traffic and the open environment create a comfortable environment for high speeds. On which approaches is speed reduction needed? Based on crash history and discussions with Caltrans staff, speeds need to be reduced in the southbound direction on Marysville Road and in the westbound direction on SR 20. B2.2 TREATMENT SCREENING Potential treatments are • Reduced lane width, • Visible shoulder treatments, • Speed tables, • Rumble strips, • Roadway environment, • Approach curvature, • Roundabouts, • Splitter islands, • Longitudinal pavement markings, • Transverse pavement markings, and • Dynamic warning sign. B2.2.1 Fatal Flaws Due to issues with visibility and awareness of the upcoming intersection, Caltrans and the research team decided that a visual treatment may be appropriate for this intersection. In addition, Case Studies: SR 20/Marysville Road 79

the agency was sensitive to cost, which eliminated the potential for roundabouts and approach cur- vature. Therefore, the team narrowed the list of treatments to the following: • Visible shoulder treatments, • Roadway environment, • Dynamic warning signs, • Transverse pavement markings, and • Longitudinal pavement markings. As shown in Exhibits B2-1 through B2-3, visible shoulder treatments, roadway environment, and longitudinal pavement markings are also “fatal flaw” treatments due to the existing road- way conditions. Visible Shoulder Treatments—Existing study roadways have minimal shoulders. Roadway Environment—There is existing vegetation prior to the intersection in the westbound direction. The open cross section and environment would have required significant changes to the roadway environment to be an effective speed reduction treatment. 80 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (Credit: Caltrans) Exhibit B2-1. Existing shoulders on SR-20. (Credit: Caltrans) Exhibit B2-2. Existing roadway environment on SR-20.

Longitudinal Pavement Markings—The existing intersection turn lanes would have made wider longitudinal pavement markings less effective or required more complex striping. B2.2.2 Evaluate Potential Treatments After the research team identified the fatal flaw treatments that were not feasible to install at this intersection, two potential treatments remained: transverse pavement markings and dynamic warning sign. At this point, the research team reviewed past research and evaluated each potential treatment to assess its effectiveness and determine which was the most appropriate. B2.2.2.1 Transverse Pavement Markings Past research has shown this treatment to be effective at reducing speeds. This treatment was chosen for the Marysville Road southbound approach to supplement existing signing and Stop Ahead pavement markings. B2.2.2.2 Dynamic Warning Sign Past research also has shown this treatment to be effective at reducing speeds and making driv- ers more aware of an upcoming intersection or roadway features. This treatment was chosen for the westbound approach of SR 20 due to the significant visual treatment that was needed to be effective at reducing speeds in a complex and open roadway environment. How much speed reduction is desired? Westbound Direction—The goal was to have drivers become more aware of the intersection and travel at or below the 55 mph posted speed limit. Southbound Direction—The goal was to reduce vehicle speeds prior to the intersection and intersection influence area, which contain the commercial land uses. Therefore, a target speed may be 55 mph or less at the stopping sight distance (SSD) to reduce speeds at the intersection approach. Where should speed be reduced? Speed reduction was needed at the southbound and westbound intersection approaches, no closer than approximately 500 ft SSD from the intersection. This would allow drivers ade- Case Studies: SR 20/Marysville Road 81 (Credit: Caltrans) Exhibit B2-3. Existing turn lanes on SR-20.

quate time to stop safely at the intersection or avoid any conflicts prior to the intersection approach. B2.3 Selecting Treatments B2.3.1 Implementation—Treatment Layout B2.3.1.1 Marysville Road—Peripheral Transverse Pavement Markings One set of markings would be located near an existing Stop Ahead sign that alerts drivers of the intersection. The markings at this location have potential to draw additional attention to those warning signs, increase drivers’ awareness of the impending intersection, and encourage drivers to reduce their speed as they approach SR 20. Another set of markings was proposed at approximately 500 ft from the intersection, which is the SSD at 55 mph, calculated based on the posted speed, using “Green Book” Exhibit 3-1. (AASHTO, 2004) B2.3.1.2 SR 20—Dynamic Warning Sign Activated by Speed In the westbound direction on SR 20, a Marysville Road sign is approximately 865 feet from the intersection. This is a reasonable distance for the radar unit (which will activate the dynamic warn- ing sign) because it would capture drivers still exceeding the maximum speed threshold even after seeing that sign. Therefore, drivers who did not reduce their speeds after viewing the road sign would have another warning approximately 370 feet later with the dynamic warning sign. The maximum speed threshold would most likely be 65 mph, based on discussions with Caltrans. The recommendation was to place the dynamic warning sign approximately 500 ft from the intersection, based on the SSD at 55 mph. This distance also allows drivers 200 ft of percep- tion–reaction time and 200 ft of deceleration using the “Green Book” Exhibit 3-1 (AASHTO, 2004) before reaching the approximate intersection influence area, which could extend approx- imately 100 ft from Marysville Road. Exhibit B2-4 illustrates a schematic of the proposed treatment layouts at the SR 20/Marysville Road intersection. B2.3.2 Treatment Design Options Full transverse bars would be more noticeable to drivers and therefore potentially more effec- tive at reducing speeds. Some agencies have received complaints from motorcyclists slipping on the markings while decelerating. Peripheral transverse bars require less maintenance than full transverse bars, are less expen- sive to install than full transverse bars (due to limited material), and potentially create a nar- rowing effect of the travelway. Note: Caltrans was interested in testing the effectiveness of peripheral transverse bars because of the simple installation and decreased maintenance associated with them. B2.3.3 Treatment Design Peripheral Transverse Bars The peripheral bars were designed to extend perpendicularly into the travelway from the edge and centerlines, but would not extend into the wheel path of vehicles. 82 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections

Exhibit B2-4. Potential treatment layout for SR 20/Marysville Road.

84 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Travelway width = 10’-6” Typical wheel base = 8’-6” Bar dimensions = 12” x 8” Exhibit B2-5. Peripheral transverse pavement marking design. (Credit: Caltrans) Exhibit B2-6. Potential dynamic warning sign design. They include five pavement markings placed in series. Peripheral bars are spaced approximately 15 ft apart. Each marking is approximately 12 to 24 in. wide and 18 to 33 in. long. The length of each peripheral bar depends on the existing lane width and width of the wheel base of vehicles that typically use the roadway. Exhibit B2-5 illustrates the proposed peripheral transverse pavement marking concept for the Marysville Road/SR 20 intersection.

Dynamic Warning Sign Activated by Speed Exhibit B2-6 illustrates the dynamic warning sign Caltrans purchased for this intersection. This treatment includes A speed limit sign and A dynamic sign showing the speeds of vehicles as they pass the detection point. Note: This is a typical sign that Caltrans has installed at other locations throughout the state. B2.3.4 Treatment Testing and Installation Caltrans was not able to install the treatments in time to be included in the research testing. However, the agency plans to implement and monitor the treatments to observe their effective- ness at reducing speeds and increasing driver awareness at the intersection. Case Studies: SR 20/Marysville Road 85

The site of this case study was the intersection of SR 26/SR 24/ S. First Avenue in Othello, Washington. B3.1 Pre-Screening The Washington Department of Transportation (WSDOT) identified this intersection as hav- ing speed and safety issues. • This intersection had a significant crash history, including two fatalities. • WSDOT implemented reduced speed zones through this corridor due to drivers not comply- ing with posted speed limits prior to this intersection. • 85th-percentile speeds were approximately 5 to 6 mph over the posted speed limits. B3.1.1 Intersection Characteristics B3.1.1.1 Traffic Volumes No traffic volume data were available for this site. B3.1.1.2 Traffic Composition • SR 26, a state facility south of, and parallel to, Interstate 90, is a secondary route that serves traffic traveling east–west through eastern Washington. • South of SR 26, S. First Avenue serves as a frontage road to SR 24. North of SR 26, S. First Avenue serves existing commercial and industrial development adjacent to the state highway. • SR 26 featured relatively high truck volumes. B3.1.1.3 Intersection Features This intersection has a two-way stop-control, with stop signs on S. First Avenue. SR 26 is a limited-access, two-lane facility. An eastbound left-turn lane, and westbound left- and right-turn lanes, are provided on SR 26. B3.1.1.4 Speed Data The posted speed limit on SR 26 was 50 mph in the vicinity of S. First Avenue. • In September 2005, the posted speed limit changed from 60 mph to 50 mph. • The speed change to 50 mph occurred 0.75 miles east of S. First Avenue in the westbound direction, and 0.90 miles west of S. First Avenue in the eastbound direction. 86 A P P E N D I X B 3 SR 26/SR 24/S. First Avenue

• A speed study was conducted on SR 26 in the vicinity of S. First Avenue in October 2005 (after the speed limit change). West of Railroad Bridge (west of S. First Avenue) • In both directions, the mean speed was 50.64; the 85th-percentile speed was 56.63. WSDOT Maintenance Shed (east of S. First Avenue) • In both directions, the mean speed was 50.48; the 85th-percentile speed was 55.43. B3.1.1.5 Crash Records Between 1999 and 2005, 74 crashes occurred at this intersection, with one fatality each in 1999 and 2004. The majority were angle crashes and those that involved vehicles traveling in opposite (i.e., left-turn and through vehicles) directions. The majority of crashes resulted in personal injury. B3.1.1.6 Environment The environment is semi-rural, with industrial and commercial developments adjacent to SR 26 and S. First Avenue. B3.1.2 Assess Data Was speed the primary issue? Were speed reduction treatments needed? • Speed limit reduction from 60 to 50 mph occurred before this intersection, and 85th-percentile speeds exceeded the posted speed limit by 5 to 6 mph in both directions. On which approaches was speed reduction needed? • SR 26 is the major roadway. • East and west approaches required speed reduction before the intersection with S. First Avenue. • S. First Avenue is a low-volume, low-speed facility. B3.2 Treatment Screening Potential treatments are • Reduced lane width, • Visible shoulder treatments, • Speed tables, • Rumble strips, • Roadway environment, • Approach curvature, • Roundabouts, • Splitter islands, • Longitudinal pavement markings, • Transverse pavement markings, and • Dynamic warning sign. B3.2.1 Fatal Flaws Reduced Lane Width—The existing lane width was 12 ft with a minimal shoulder and guardrail. Potential risks existed because of high truck volumes. Visible Shoulder Treatment—Existing shoulders (see Exhibit B3-1) featured a fairly steep slope behind the guardrail, which prevented effective visual shoulder treatments. Case Studies: SR 26/SR 24/S. First Avenue 87

Note: WSDOT staff indicated a fill slope of approximately 1.5:1. Therefore, shoulder treat- ment was not feasible. Speed Tables—Since 85th-percentile speeds were greater than 55 mph, speed tables would not be appropriate for this high-speed roadway. Rumble Strips—A high volume of truck traffic and several adjacent industrial and commer- cial land uses exist. Note: WSDOT was not interested in installing rumble strips on SR 26 due to the freeway-like conditions. Roadway Environment—The existing guardrail, narrow shoulders, and steep grades made it difficult to install effective roadway environment treatments such as landscaping. Approach Curvature—Right of way and lane geometry was constrained. Roundabout—An imbalance of traffic volumes existed between SR 26 and S. First Avenue. In addition, the south approach would have required complex geometry. WSDOT also did not have the funds to build this type of treatment. Splitter Island—This treatment is typically used on stop-control approaches. B3.2.2 Evaluate Potential Treatments After the research team identified the fatal flaw treatments that were not feasible to install at this intersection, three potential treatments remained: longitudinal pavement markings, trans- verse pavement markings, and a dynamic warning sign. At this time, the research team reviewed past research and evaluated each potential treatment to assess its effectiveness and determine which one was the most appropriate. B3.2.2.1 Longitudinal Pavement Markings Research did not show these to be effective speed reduction treatments because • They require a large amount of pavement material, depending on the treatment boundary. • They are possibly more effective in areas with speed adaptation issues or a large number of elderly drivers. 88 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (Credit: WSDOT) Exhibit B3-1. Existing shoulders on SR 26.

B3.2.2.2 Transverse Pavement Markings Past research had shown this treatment to effectively reduce speeds. The eastbound left-turn lane and wider intersection pavement made it difficult to design treat- ments near the intersection approach. B3.2.2.3 Dynamic Warning Signs WSDOT had funds to purchase and install a dynamic warning sign. • This type of treatment had been effective in reducing vehicle speeds in similar roadway envi- ronments. • WSDOT was interested in designing a dynamic warning sign that combined a speed limit and Intersection Ahead sign with a dynamic message sign. How much speed reduction is desired? In the eastbound and westbound directions, the desired speed was 50 mph to meet posted speed guidelines. The target speed (maximum speed threshold) to activate the sign was set at 54 mph, based on the posted speed limit and the existing 85th-percentile speeds. Where should speed be reduced? Speed reduction was needed at the eastbound and westbound intersection approaches, no closer than approximately 500 feet (SSD) from the intersection. B3.3 Selecting Treatments B3.3.1 Implementation—Treatment Layout Exhibit B3-2 illustrates a schematic of the proposed treatment layouts at the SR 26/SR 24/ S. First Avenue intersection. SR 26 eastbound and westbound approaches • Dynamic warning signs were located approximately 850 ft from the intersection in both direc- tions. • The sign location was based on the estimated perception-reaction time, deceleration, and stopping sight distance from S. First Avenue. Sign location also was determined based on con- straints with the steep shoulder grades and existing bridge. • The radar unit was placed on the sign to detect vehicle speeds in advance of the sign. Note: WSDOT also observed that a power source existed near this location, making installa- tion feasible. B3.3.2 Treatment Design Options Potential Options Various treatment design options for this dynamic warning sign existed, including: • Your Speed Is XX, • Slow Down, or • Caution. Case Studies: SR 26/SR 24/S. First Avenue 89

Exhibit B3-2. Preliminary treatment layout for SR 26/S. First Avenue.

WSDOT Sign Design The dynamic warning sign at this location is shown in Exhibit B3-3 and was designed to include the messages, Speed Limit 50 and Intersection Ahead. A dynamic message also flashes SLOW (1.5 seconds), DOWN (1.5 seconds) and then is blank for 1.5 seconds. Radar Unit The radar unit was attached to the sign, as shown in Exhibit B3-4. The maximum speed threshold for the radar unit was set at 54 mph. Case Studies: SR 26/SR 24/S. First Avenue 91 (Credit: WSDOT) Exhibit B3-3. Dynamic warning sign design. (Credit: WSDOT) Exhibit B3-4. Radar unit.

B3.3.4 Treatment Testing and Installation • May 2006—“Before” testing, • September 2006—Treatment installation, and • March 2007—“After” testing. Note: Traffic control was required during the before-and-after testing due to high volumes and speeds on SR 26. The dynamic message attached to the overall sign was not shipped to WSDOT until late August. Therefore, the sign was not installed until September 2006. Due to the late installation date and desired acclimation period, “after” testing was conducted by the research team in March 2007. This provided an acclimation period of approximately six months. Exhibit B3-5 illustrates the installed dynamic warning signs along eastbound and westbound SR 26. 92 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections (Credit: WSDOT) (Credit: WSDOT) (a) Eastbound (b) Westbound Exhibit B3-5. Dynamic warning signs along SR 26.

The site of this case study was the intersection of Macksburg Road and Canby-Marquam Highway in Clackamas County, Oregon. B4.1 Pre-Screening Clackamas County identified this intersection as having speed and safety issues. These issues included run-off-the-road crashes northbound on Canby-Marquam Highway. B4.1.1 Intersection Characteristics B4.1.1.1 Traffic Volumes Canby-Marquam Highway has higher traffic volumes than Macksburg Road. Canby-Marquam Highway has approximately 6,800 to 7,000 ADT during a typical weekday. Note: Moderate volume provides opportunities for drivers to travel at free-flow speeds, espe- cially during non-peak periods. B4.1.1.2 Traffic Composition A high percentage of agricultural truck traffic exists at this site. B4.1.1.3 Intersection Features This is a stop-controlled, T intersection, with a stop sign on the east approach of Macksburg Road. • Canby-Marquam Highway and Macksburg Road are two-lane roadways. • No dedicated left-turn lanes exist on Canby-Marquam Highway. • Macksburg Road forms an intersection in the middle of a curve on Canby-Marquam Highway. B4.1.1.4 Speed Data The posted speed is the “Basic Rule.” Note: Although the county does not have speed data for this intersection, they believe that reducing vehicle speeds may decrease intersection crashes. B4.1.1.5 Crash Record No intersection crash data was provided for this intersection. Note: Based on discussions with the county, there is a history of run-off-the-road crashes in the northbound direction. Drivers involved in crashes did not anticipate the existing curve at the 93 A P P E N D I X B 4 Macksburg Road/Canby-Marquam Highway

intersection, which resulted in vehicles running off the road into the residential property at the intersection’s northeast corner. B4.1.1.6 Environment The surrounding area is rural and open. Farms are located on the northeast corner and across from the intersection west of Canby- Marquam Highway. B4.1.2 Assess Data Is speed the primary issue? Are speed reduction treatments needed? • A closer review of the roadway geometry (see Exhibit B4-1) revealed that the run-off-the-road crashes were most likely due to the roadway curvature at the intersection, rather than high speeds. • The alignment of the curvature made it difficult for drivers to observe the approaching road- way. • The actual presence of an intersection may not have impacted the crashes. • Although a speed reduction treatment would help reduce vehicle speeds in advance of the intersection, the team did not move forward with this candidate site because speed was not the primary problem and a segment issue may have existed rather than an intersection issue. • Installing chevrons along the curve or other signage may make drivers more aware of the exist- ing roadway curvature. • In the long term, the roadway and intersection may need to be realigned to provide a more gradual curve radius for vehicles traversing the road. 94 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Exhibit B4-1. Aerial view of Macksburg road.