ORANGE COUNTY TRAFFIC COMMITTEE
ORANGE COUNTY TRAFFIC COMMITTEE
COMMITTEE REPORT OF: February 15, 2007 ITEM AJanuary 18, 2007 ITEM A
SUPERVISORIAL DISTRICT: 5
SUBJECT: Speed Limit
LOCATION: Narrow Canyon Road; Ladera Ranch; TB 952 D2, E2, E3
INITIATED BY: Road/Traffic Engineering
REQUEST: Establish a posted speed limit on Narrow Canyon Road between O’Neill Drive and Ethereal Street.
Item was continued from the January 18th traffic committee meeting.
DATA:
EXISTING CONDITIONS
Narrow Canyon Road is a 1.1 mile long Residential Collector Street within the unincorporated South-County community of Ladera Ranch. It gradually curves from O’Neill Drive south-westerly then easterly to Ethereal Street with a few horizontal curves. The outside curb-to-curb width of this roadway varies from 40’ to 56’ with 18’ to 20’ of traveled width. This roadway has intermittent raised median, but no continuous center line striping. On-street parking is prohibited where raised median is present and separate left-turn pockets are provided at certain intersections. Three roundabouts are located along Narrow Canyon Road: at O’Neill Drive, Ethereal Street, and Clarin Street. Other side streets are one-way stop controlled. There is direct residential frontage of attached condominiums on portions of one side of Narrow Canyon Road. For the majority of length of Narrow Canyon Road, the area beyond the sidewalks consists of roadside greenbelts and landscaped slopes. Typical appropriate signs are posted throughout the collector street including preceding the roundabouts. Two public parks are located along Narrow Canyon, near the intersection of Aura and near the roundabout at Ethereal Street. At the intersection of Aura, a pre-school facility with 134-student enrollment just opened on 1/15/07.
SPOT SPEED DATA
85th 10MPH % Total
Location Date Percentile Pace In Pace Vehicles
Narrow Canyon Rd South of Quartz 10/04/06 37 mph 29-38 77 104
Narrow Canyon Rd South of Aura 10/04/06 41 mph 32-41 68 114
TRAFFIC VOLUMES (ADT)
Location Date ADT AM PEAK PM PEAK
Narrow Canyon Road n/o Quartz 12/07 3579 269/ 7 am 270/ 6 pm
SIGHT DISTANCE:
| |Left [ft] |Comment |Right [ft] |Comment |
|Orange Blossom Cir |392 | |OK |Up to roundabout |
|Quartz Ln |370 |If No Parking on East Curb, S > 390’ |270 |If trimming down bushes, S > 390’ |
|Gaia Ln |OK | |OK | |
|Aura Ln. E. |OK | |OK | |
|Aura Ln W. |250 |Signage board and construction fence block |OK | |
| | |the view. If move stop line 10’ forward, S ~| | |
| | |360’ | | |
|Menlo St |OK | |390 |Trimming down bushes on East curb to |
| | | | |improve S |
|Thoreau St. |220 |View is completely blocked by bushes. |400 |View can be maximized by tree trimming |
| | |Trimming down bushes on East curb all the way| |and No Parking on East curb |
| | |can increase S to 300’. | | |
|Barretts Wy. |OK |Up to roundabout |240 |Trimming down bushes and trees and |
| | | | |Posting No Parking on East curb may |
| | | | |increase S to 300’ |
|Clarin St Roundabout | | | | |
|Vanstone Ct |254 |Even trimming down bushes & trees and No |OK |Up to roundabout |
| | |parking on East curb, S is sill < 300’ | | |
|Epona Wy |OK | |OK | |
|Unmarked Xwalk |OK | |250 |Limited by horizontal curvature |
|Acaster Wy |245 |Even trimming down bushes & trees and No |390 |Limited by horizontal curvature |
| | |parking on East curb, S is still < 300’ | | |
|Unmarked Xwalk ( |300 |Up to roundabout |OK | |
* RDMD Standard Plan: Intersection Sight Distance (S) >= 390 ft or Stopping Sight Distance (S(s)) >= 250 ft
* Above highlighted locations do not meet the standard Intersection Sight Distance for 35 mph design speed.
ACCIDENT DATA
The subject study area is one of the newest communities in Ladera Ranch; therefore, no accident data is available prior to the past twelve months. Two accidents occurred within the most current twelve months; both resulted in property damage along at the west side of Narrow Canyon near Quartz. Both drivers were traveling southerly at an unknown high rate of speed and failed to negotiate the curve to the left.
ANALYSIS
The California Vehicle Code (CVC) requires that an established speed limit be based on the findings of an “engineering and traffic survey” to be radar enforceable. This survey considers three essential elements; the prevailing speeds determined by traffic engineering measurements, collision records, and highway, traffic and roadside conditions not readily apparent to the driver (CVC Section 627). The 2006 California Manual on Uniform Traffic Control Devices (CA MUTCD) Section 2B.13 further specifies “other factors that may be considered when establishing speed limits are the following:
A. Road characteristics, shoulder condition, grade, alignment, and sight distance;
B. The pace speed;
C. Roadside development and environment;
D. Parking practices and pedestrian activity; and
E. Reported crash experience for at least a 12-month period.”
The CA MUTCD requires the posted speed limit to be established at the nearest 5 mph increment to the 85th percentile speed of free-flowing traffic. A 5 mph reduction may be taken where engineering study indicates the need for a reduction in speed to match existing conditions with the traffic safety needs of the community. (CA MUTCD Section 2B.13)
Radar speed measurements were taken at two locations on Narrow Canyon Road in October, 2006. Measurement one was taken south of Quartz showing an 85th percentile speed of 37 mph. The 10 mph pace is between 29-38 mph with 77% of the vehicles observed in pace. Measurement two was taken south of Aura with an 85th percentile speed of 41 mph. The 10 mph pace is between 32 – 41 mph with 68% of the vehicles observed in pace.
Two accidents were reported on this roadway within the past 12 months, both of which occurred near the intersection of Quartz. The common characteristic shared by these two accidents is excessive travel speed causing vehicles to swing towards outer radius curbside.
The roadway was designed to meet minimum Orange County Collector Street (35 mph) design standards except the curving segment between Vanstone and Epona. The centerline radius of this segment is 460 feet instead of the minimum required radius of 550 feet for a 35 mph design speed with no super-elevation imposed. Applying the methodology shown in Orange County Highway Design Manual Figure 203.2, the comfortable travel speed on a collector street with 460 feet turning radius is approximately 34 mph. Five out of eleven intersections along Narrow Canyon meet or can meet the minimum intersection sight distance for the 35 mph design speed. Six intersections meet or can meet the minimum stopping sight distance standards for 35 mph. Many of the intersections have sight distance restricted by landscaping or parked vehicles as indicated in the sight distance table; eliminating on-street parking and modifying landscaping near the five intersections are necessary to achieve the sight distances identified.
Narrow Canyon functions as a local residential collector street with no direct residential vehicular access,access; block walls or slopes separating rear yards comprise much of the road. A portion of the length of the roadway on the east side has residential condominium frontage with front doors and sidewalks connecting to the street; as a result there is pedestrian activity and parking not typical to a collector street.
The speed survey for the portion south of Aura shows an 85th percentile speed of 41 mph, although the design speed and sight distance for Narrow Canyon Road is 35 mph. Many intersections only meet minimum stopping sight distance for a 35 mph posting. The high density condominiums located on one side of the roadway with front doors facing the street serves to give Narrow Canyon Road a more residential-like character. The sidewalk is also heavily used by joggers and dog-walkers. And, rRather than having continuous smooth centerline curves, the roadway has intermittent raised medians, which motorists must navigate by adjusting their location in the travel way as they pass thru the area.
At the January meeting, the main issue discussed by the Committee was the appropriateness of reducing the speed limit by 5 mph from 85th % speed of 40 mph; certain committee members considered the 85th % to be a more appropriate speed limit based on the data presented. According to the CA MUTCD Section 2B.13, the posted speed limit may be reduced by 5 mph from the nearest 5 mph increment of the 85th-percentile speed where an engineering study indicates the need for a reduction in speed to match existing conditions with the traffic safety needs of the community. Factors such as road characteristics, sight distance, roadside development, and pedestrian activity may be considered when establishing speed limits. Greater care must be used when setting a speed limit 10 mph or more below the 85th percentile% speed.
Narrow Canyon Rroad, unlike many other typical collector streets, does have a more residential-like characteristic due to the adjacent housing type (40% of the roadway has residences directly fronting the road) and also has a higher rate of pedestrian activity due to the adjacent housing and public amenities. The recently opened preschool at the corner of Aura, a new roadside development, also brings the potential of additional people walking on the nearby sidewalks as a large number of homes are within easy walking distance of the pre-school. The road provides access only to the Terramor residential community with no through traffic and was designed with a curvilinear alignment and raised medians to encourage a lower travel speed.
Sight distance is another factor that may be considered when setting the speed limit. As stated in the above Sight Distance table, many intersections only meet, or can meet with mitigation, the minimum stopping sight distance of 250 feet for 35 mph for drivers on Narrow Canyon as they approach the various intersections. Interpolating from the information in Orange County Standard Plan #1117, a speed of 40 mph would require a minimum stopping sight distance of 305 feet, which many of the intersections on Narrow Canyon Road would not meet even with the mitigation proposed for landscaping and reduced on-street parking. Based on the Orange County Highway Design Manual Figure 203.2, the minimum centerline radius for a speed of 40 mph is 711 feet; over 70% of the length of Narrow Canyon Road was constructed for a maximum design speed less than 40 mph.
As a residential product, Narrow Canyon Road was clearly designed to meet the community’s needs to limit the ability of traveling more than 35 mph with many physical features such as the use of curve radii, intermittent raised medians and roundabouts.
Based on these facts and the conditions mentioned above, staff recommends that a 35 mph radar enforced prima facie speed limit be established on this 1.1 mile roadway segment.
PUBLIC COMMENTS AND INPUTS
Two speakers addressed the Committee in which they supported the recommendation to the Traffic Committee.
COMMITTEE DISCUSSION AND RECOMMENDATIONS
The Committee discussed the minimum stopping vs. intersection sight distance for the side streets of Narrow Canyon Road. The Committee member also discussed the details landscaping and parking instruction of mitigations recommended. The Committee determined that the factors such as road characteristic, roadside development, pedestrian activity, alignment and sight distance should be considered when setting posted speed limit. A motion was made and approved to support the staff recommendation.
RECOMMENDATION
Establish a 35 mph speed limit on Narrow Canyon Road between O’Neill Drive and Ethereal Street and post appropriate signage to allow radar speed enforcement.
Eliminate parking zones on the west side of the roadway at Quartz Lane and the east side of the roadway at Thoreau Street, Barretts Lane, Vanstone Court and Acaster Way.
Trim down bushes at intersections of Quartz Lane, Thoreau Street, Barretts Way, Vanstone Court, and Acaster Way.
BOARD ACTIONS NECESSARY TO ENACT THIS RECOMMENDATION
1. Approve this report.
2. By resolution, establish a 35 mph prima facie speed limit on Narrow Canyon Road between O’Neill Drive and Ethereal Street.
3. By resolution, eliminate parking zones at the following five intersections: Quartz, Thoreau, Barretts, Vanstone and Acaster.
4. By resolution, trim down bushes at the following five intersections: Quartz, Thoreau, Barretts, Vanstone and Acaster.
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