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APPENDIX B
Case Studies
68
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APPENDIX B1
Whiskey Hill Road/Meridian Road
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."
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70 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
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.
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Case Studies: Whiskey Hill Road/Meridian Road 71
· 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.
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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.
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.
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Case Studies: Whiskey Hill Road/Meridian Road 73
Exhibit B1-2. Residences near Whiskey Hill
and Meridian 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.
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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.
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.
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Case Studies: Whiskey Hill Road/Meridian Road 75
Exhibit B1-4. Schematic of Whiskey Hill Road/Meridian Road intersection
proposed treatment layouts.
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76 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
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.
Exhibit B1-5. Peripheral transverse pavement marking design.
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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.
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APPENDIX B2
SR 20/Marysville Road
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.
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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.
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.
(Credit: Caltrans)
Exhibit B2-6. Potential dynamic warning sign
design.
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Case Studies: SR 20/Marysville Road 85
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.
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APPENDIX B3
SR 26/SR 24/S. First Avenue
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 eastwest 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.
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Case Studies: SR 26/SR 24/S. First Avenue 87
· 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.
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88 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
(Credit: WSDOT)
Exhibit B3-1. Existing shoulders on SR 26.
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.
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Case Studies: SR 26/SR 24/S. First Avenue 89
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.
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Exhibit B3-2. Preliminary treatment layout for SR 26/S. First Avenue.
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Case Studies: SR 26/SR 24/S. First Avenue 91
(Credit: WSDOT)
Exhibit B3-3. Dynamic warning sign
design.
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.
(Credit: WSDOT)
Exhibit B3-4. Radar unit.
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92 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
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.
(Credit: WSDOT) (Credit: WSDOT)
(a) Eastbound (b) Westbound
Exhibit B3-5. Dynamic warning signs along SR 26.
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APPENDIX B4
Macksburg Road/Canby-Marquam
Highway
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
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94 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
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.
Exhibit B4-1. Aerial view of Macksburg road.
