COUNTY OF SAN MATEO

Inter-Departmental Correspondence

Department of Public Works

DATE:

February 20, 2002

BOARD MEETING DATE:

March 5, 2002

TO:

Honorable Board of Supervisors

FROM:

Neil R. Cullen, Director of Public Works

SUBJECT:

Traffic Signal at the Intersection of Edgewood Road and Cordilleras Road (West) - Redwood City Area

Recommendation

Determine if staff should proceed with the design and installation of a traffic signal at the westerly intersection of Edgewood Road and Cordilleras Road; and if your Board directs us to proceed with the traffic signal design, determine:

a)

if a separate left-turn lane (Edgewood Road west onto Cordilleras Road) should be provided in conjunction with the signal; or

b)

if the left-turn movement on Edgewood Road west onto Cordilleras Road should be eliminated or restricted during certain hours.

Staff Recommendation

Direct staff to:

·

proceed with the design of a traffic signal at the westerly intersection of Edgewood Road and Cordilleras Road without a separate left-turn lane (Edgewood Road west onto Cordilleras Road); and

·

develop and present to your Board an ordinance that prohibits left-turn movements from Edgewood Road onto Cordilleras Road at this intersection.

Previous Board Action

Authorized the installation of a traffic signal at Edgewood Road and Scenic Drive. The signal installation did not include a separate left-turn lane and traffic is prohibited from making left-turns during the morning peak hour period.

Key Facts

1.

The westerly intersection of Edgewood Road and Cordilleras Road meets the necessary warrants for the installation of a traffic signal.

2.

The installation of a left-turn lane on Edgewood Road at this intersection would require excavation into San Francisco Water Department property, the construction of large retaining walls, the encroachment into the riparian corridor of Cordilleras Creek or the change in the bicyclists' use of Edgewood Road in this area.

3.

Prohibiting left turns off of Edgewood Road will reduce the potential for rear-end type accidents at this intersection that could increase with the installation of a signal without a left turn storage lane.

Discussion

Edgewood Road is a primary east/west road that provides a connection to Interstate 280 for approximately 16,000 motorists per day from Redwood City, San Carlos, and the unincorporated areas of Palomar Park, Oak Knoll and Emerald Lake Hills. The road also provides a connection to the popular bicycling area in Woodside and Portola Valley via Canada Road.

We evaluated the intersection of Edgewood Road and Cordilleras Road (West) as residents in the Emerald Lake Hills and Redwood City area have complained that it is difficult at best to make left-turns onto Edgewood Road from Cordilleras Road due to the volume and speed of the traffic on Edgewood Road. We determined that the intersection meets State of California Traffic Warrants for signalization based on the volume of traffic and accident history.

Left-Turn Lane on Edgewood Road

We also evaluated the installation of a left-turn lane to provide a protected area for motorists who want to turn left onto Cordilleras Road from Edgewood Road. Widening the intersection to provide the room for a left-turn lane is difficult at best as:

·

water transmission lines that are part of the San Francisco Water Department's Hetch Hetchy Water transmission system are located on San Francisco Water Department property just north of the road; and

·

Cordilleras Creek is on the south side of the road.

Widening to the north would require excavation into the Water Department property or large retaining walls; and widening to the south would encroach into the riparian corridor of Cordilleras Creek. These options have significant monetary impacts in terms of increased construction costs, and may have environmental impacts that would at best have to be mitigated. The option may also require the acquisition of a portion of the adjacent properties.

The left-turn lane could also be accommodated by eliminating the shoulders of the road in this area. However, this option also eliminates the shoulder area for bicyclists and would require that they merge into the traffic lanes through the intersection area. Cordilleras Road could also be signed as a bicycle route to make bicyclists aware of Cordilleras Road as an optional route, that has a flatter grade (i.e., easier bicycling) than Edgewood Road. However, the provisions of the California Vehicle Code precludes us from prohibiting bicyclists from using a road even in an area where the road's shoulders are eliminated.

Split Phase Signal

We also considered a split phase signal system (separate phasing for traffic going west and east on Edgewood Road) to provide for the left-turn movement off of Edgewood Road. However, we are not recommending this as an alternate as this type of signal phasing led to a significant increase in traffic congestion when this phasing was previously implemented for a short time at the intersection of Edgewood Road and Scenic Drive.

Prohibiting Left-Turns Off of Edgewood Road at Cordilleras Road West

The stopping sight distance for motorists approaching this intersection from the east (i.e., traveling west) is not as great as the stopping sight distance for motorists approaching the Edgewood/Scenic Drive intersection where left-turns are allowed at off peak hours. We believe that the potential for rear end type traffic accidents involving motorists waiting to turn left onto Cordillera Road will increase if the signal is installed without a left-turn pocket and left-turns continue to be allowed. However, we also believe that prohibiting the left-turn movement onto Cordilleras Road from Edgewood Road will inconvenience the least amount of motorists and avoid the environmental and fiscal impacts associated with the construction of a left-turn pocket.

Impact on Traffic at Edgewood Road at Cordilleras Road East

Our traffic counts indicate that approximately 125 motorists, who currently make the left-turn at this intersection, will be diverted to the easterly connection of Cordilleras Road. This would either increase the turn movements at Cordilleras east from approximately 800 to 925 turns per day which is not considered excessive, or motorists will seek another route to access the area. There is a daycare center located on the northerly side of Edgewood Road near the Cordilleras east intersection, and parents currently park on the shoulder of the road when picking up or dropping off their children. Motorists parked on the shoulder coupled with motorists waiting to turn at the intersection may result in an increase in the periodic backup of traffic at this location.

Other Agencies/Groups Contacted

We had previously contacted the Cities of Redwood City and San Carlos, the Palomar Park Homeowners Association and the Emerald Hills Association, and the California Highway Patrol and asked their opinion with regards to the installation of the signal and the prohibition of the left-turns off of Edgewood Road. There was not a consensus of opinion that the signal should be installed as some were concerned that the signal would impact the flow of traffic on Edgewood Road and that a left-turn lane should be installed in lieu of the signal. We have sent the same agencies/groups as well as the City/County Association of Governments Bikeways Committee a copy of our report and have notified them as to the tentative date when this report is scheduled to be considered by your Board. We will report any comments that we receive. We have also sent the report to individuals that have commented on the intersection in the past and to the property owners near the intersection.

Vision Alignment

We believe our recommendation is consistent with Goal Number 7, "Maintain and Enhance the Public Safety of all Residents and Visitors" of the Shared Vision Commitment to "Ensure Basic Health and Safety for All," as the installation will improve the safety for motorists turning onto Edgewood Road without compromising the safety of other motorists.

Fiscal Impact

The estimated cost of the work including design and construction is $110,000. This cost is proposed to be financed with Road Funds. There is no impact to the General Fund.

The San Mateo County Planning Department has determined that the project without the left-turn lane is exempt from the requirements for preparation of an EIR under Section 15303, of the California Environmental Quality Act. However, we will not file the necessary Notice of Exemption with the County Clerk until direction is given by your Board and the impacts of any revisions in the proposed project evaluated.