TO: Board of Supervisors
FROM: Steven Lederer, Director of Public Works
REPORT BY: Syed Ahsan Kazmi, P.E., Senior Traffic Engineer, Public Works
SUBJECT: Coombsville Road at 1st Avenue and 4th Avenue Traffic Control Assessment Study
RECOMMENDATION
title
Director of Public Works requests adoption of a Resolution establishing stop control for the eastbound and westbound traffic on Coombsville Road at its intersection with 4th Avenue.
body
EXECUTIVE SUMMARY
At a Coombsville Community Meeting on June 30, 2023, several residents raised safety and line of sight related concerns at the intersection of Coombsville Road at 1st Avenue and similar concerns at 4th Avenue. Public Works staff requested the Fehr and Peers (F&P) Engineering Consulting Firm to conduct a traffic safety survey and prepare a report on Coombsville Road at the 1st Avenue and 4th Avenue intersections.
F&P’s report recommends installation of stop signs for eastbound and westbound traffic on Coombsville Road at 4th Avenue to provide a three-way stop intersection due to limited line of sight for safe traffic operations (4th Avenue already has a stop sign). The report does not recommend installing stop signs on Coombsville Road at the 1st Avenue intersection because none of the state established all-way stop control warrants are met, which are based on traffic volumes (motor vehicles, pedestrians, and bicyclists), vehicular speed, collision data and line of sight. The report indicates traffic calming measures at 1st Avenue should be implemented to improve safety conditions for motor vehicles, bicyclists, and pedestrians.
The proposed Resolution will authorize installation of an all-way stop control on eastbound and westbound Coombsville Road at 4th Avenue. The Director of Public Works intends to implement traffic calming measures at Coombsville Road and 1st Avenue (no Resolution is required for that action).
FISCAL & STRATEGIC PLAN IMPACT
|
Is there a Fiscal Impact? |
Yes |
|
Is it currently budgeted? |
Yes |
|
Where is it budgeted? |
The Roads Division budget provides funding each year for installation, modifications and maintenance to various traffic control signs and markings. The recommended action will require the installation and/or modification of regulatory, advisory, and warning signs. These actions are routine and are included within the current budget. |
|
Is it Mandatory or Discretionary? |
Discretionary |
|
Discretionary Justification: |
The proposed action is necessary to allow safe and efficient traffic condition for pedestrians, bicyclists, and motorists. |
|
Is the general fund affected? |
No |
|
Future fiscal impact: |
None |
|
Consequences if not approved: |
Traffic control at the intersection will remain the same. |
|
County Strategic Plan pillar addressed: |
Effective and Open Government |
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed activity is categorically exempt from CEQA pursuant to CEQA Guidelines section 15301, as relating to the operation of existing public facilities involving negligible or no expansion of existing or former use.
BACKGROUND AND DISCUSSION
California Vehicle Code sections 21100(d), 21351, and 21355 authorize local authorities to erect stop signs on roadways within its jurisdiction. California Vehicle Code section 21401 requires traffic control devices (including stop signs) to conform to the California Manual of Traffic Control Devices (CA MUTCD).
Section 2B.04 of the California Manual of Traffic Control Devices (CA MUTCD) indicates that yield or stop signs should not be used for speed control. Further, a yield or stop sign should not be installed on the higher volume roadway at an intersection unless justified by an engineering study. Section 2B.05 further indicates a stop sign is not a “cure-all” and is not a substitute for other traffic control devices. Often, the need for a stop sign can be eliminated if the sight distance is increased by removing obstructions.
Section 2B.07 of the CA MUTCD indicates multi-way stop signs are used where the volume of traffic on the intersecting roads is approximately equal. Installation of multi-way stop signs should also be based on an engineering study, including whether there were five or more reported crashes in a 12-month period that are susceptible to correction by a multi-way stop installation. Such crashes include right-turn and left-turn collisions as well as right-angle collisions and the need to control left-turn conflicts.
In response to concerns raised by the Coombsville community and member of the Napa County Board of Supervisors, Fehr & Peers Engineering Consulting Firm (F&P) was asked to perform an intersection traffic control warrant study to determine if an all-way stop control (AWSC) is warranted at the following two intersections:
• Coombsville Road/1st Avenue
• Coombsville Road/4th Avenue
Assessment provided in the traffic report includes collecting and reviewing traffic volumes, collision history, and site visit to observe sight lines at the side street approaches. This evaluation was performed in accordance with the CA-MUTCD, Policy on Geometric Design of Highways and Streets (The AASHTO Green Book), and California Highway Design Manual (HDM) standards.
METHODOLOGY
All Way Stop Control Warrants: The 2014 California Manual on Uniform Traffic Control Revision 7 (CA- MUTCD) provides criteria for the evaluation of an all-way stop control (AWSC). If any of the following criteria are met, installation of stop control on all approaches may be warranted. However, meeting a warrant criterion does not automatically justify the installation of traffic control as there may be other factors to consider.
Criteria 1:
1) Major street volumes exceed 300 vehicles per hour for any eight hours of a day,
2) Minor street volumes exceed 200 units (Units include bicycles, pedestrians, and vehicles) per hour for the same eight hours, and
3) Average vehicle delay for the side street exceeds 30 seconds per vehicle in the peak hour.
Criteria 2:
Insufficient sight distance (Sight distance standards defined by AASHTO, 6th Edition).
Criteria 3:
At least five crashes within the last year that can be corrected by all-way stop-control.
Intersection Evaluations:
Coombsville Road at 4th Avenue:
In the vicinity of 4th Avenue, Coombsville Road is a two-lane east-west Roadway and forms a three-legged intersection with 4th Avenue. 4th Avenue is a two-lane residential street. The 85th percentile speed calculated east and west of this intersection was found to range from 39 to 42 mph, demonstrating that motorists generally travel at about the posted speed limit.
At the 4th Avenue approach, line of sight from the motorists on 4th Avenue and westbound traffic is obstructed by the existing outcropping of bushes and trees at the southeast corner of the intersection. During a field visit, measured distance a motorist on the side street can see to the east (looking at oncoming westbound traffic) is about 110 ft. Provided that data collection found that the westbound 85th percentile speed for the westbound approach was 42 mph, a Stopping Sight Distance (SSD) of approximately 340 ft would be necessary to meet applicable sightlines at this intersection. The line of sight could be improved with removing plantings and trees and installing a vertical wall along the existing fence line. With that improvement, an estimated line of sight could be increased from about 110 ft to 225 ft. Even with that improvement, the line of sight provided would not be adequately long enough for motorists to make decisions to enter the roadway.
Review of five years of collision data (2018-2023) indicate two (2) rear end collisions were recorded with another motor vehicle due to unsafe speed and driving under influence. This intersection is not meeting the minimum number of collisions criteria for AWSC but does have sight vision concerns as discussed above.
Based on the methodology and analysis presented above, the traffic report recommends:
Due to the limited sight lines observed at this intersection, an all-way stop control is recommended to be implemented at the Coombsville Road and 4th Avenue intersection. In addition, the County will trim plantings and trees to maximize sightlines for westbound motorists and motorists waiting on the 4th Avenue approach.
It is recommended that the Board of Supervisors approve the proposed signing and striping configuration at the intersection of Coombsville Road and 4th Avenue. If the stop control is approved, the California Highway Patrol will be informed of the change.
Coombsville Road and 1st Avenue:
Coombsville Road is a two-lane east-west collector that provides a connection between downtown City of Napa and the Napa County neighborhoods directly east of downtown. The posted speed limit along this corridor in the vicinity of study locations is 40 mph. 1st Avenue is a two-lane collector street that has residences fronting the roadway and provides a connection to Hagen Rd to the north. 1st Avenue tees into Coombsville Road. The intersection of Coombsville Road and 1st Avenue is side street stop controlled.
The 85th percentile speed in both directions east and west of the intersection is between 42 and 45 mph, which is within 5 mph of the posted speed limit. This does not trigger any improvement or countermeasure.
According to the Caltrans Highway Design Manual (HDM), the SSD for a design speed of 40 mph is 305 feet and the SSD for a design speed of 45 mph is 360 feet. At the 1st Avenue approach, a motorist waiting to turn from 1st Avenue to Coombsville Road can see more than 600 ft to the west and over 400 ft to the east. This line of sight (in each direction) is greater than the corresponding SSD for traffic approaching at the maximum observed 85th percentile speed of 45 mph.
Five years of collision data (2018-2023) was reviewed in the vicinity of Coombsville Road/1st Avenue. Seven (7) collisions were reported. In all cases the collisions were classified as “Hit Fixed Object”, and the primary cause was improper turning (4), driving under influence (2), and unsafe speed (1). As such this intersection does not meet the minimum number for AWSC.
Recommendations: Based on the methodology and analysis presented above, the traffic report recommends that the County make improvements that would further increase visibility, provide advanced warning to motorists in the eastbound and westbound directions, and reduce the operating speed of motorists along Coombsville Road, including:
Landscaping Maintenance:
The County or the property owner will proactively trim overgrown trees and plantings on the south side of Coombsville Road on the westbound approach to the 1st Avenue intersection.
Pavement Markings and Surface Treatments:
The County will add speed limit pavement markings along the corridor. Additional reflective surface mounted markers will be considered at the intersection to increase visibility for the centerline and approach lanes.
Advanced Warning Signs:
Advisory speed signs with solar powered LED double-sided chevrons with yellow reflective posts will be installed on the curve on the east side of the intersection.
LED Stop Sign:
We will investigate the potential to upgrade the existing stop signs on 1st Ave. and Coombsville and 1st Ave. and Hagen Rd. to a solar-powered LED stop sign to improve visibility.
Radar Feedback Signs:
The County will install a radar feedback sign for westbound traffic approaching both the 1st Ave. and 4th Ave. intersections.
CROSS TRAFFIC DOES NOT STOP Sign:
Additional signage will be added at the intersection to warn vehicles approaching from 1st Avenue that cross traffic does not stop.