Street Sweeping provided by CleanStreet.

Arterial and Collector roads are swept once a month on the 2^nd Tuesday of the month while residential roads are swept four times per year or once per quarter year. 

Sun, heat and vehicle loads can break down roads, but the biggest enemy of a road is water. When water gets underneath the pavement, the road becomes weaker and, as vehicles use the road, the weakened parts of the pavement start pumping up and down and a pothole is born. To protect our roads from water seepage, the Town routinely patches or seals cracks and damaged areas. This helps to prolong the life of the road to avoid costly resurfacing or reconstruction.

The pavement condition of Portola Valley’s street network is evaluated every 2 to 5 years. The condition survey grades the streets using a rating standard called Pavement Condition Index (PCI) which ranges from 0 to 100 with 100 representing an excellent pavement.

How Streets Are Selected for Projects

The Public Works Department consider the PCI scores of streets, the timing of public projects for water and sewer infrastructure, and the limited funding when selecting streets for a project. 

The town generally maintains its streets using surface seal methods and rehabilitates its streets using grind and overlay methods.  The Town uses surface seal methods by applying water-proof seal coats to the asphalt surface to prevent pavements from deteriorating over time due to water permeation beneath the asphalt layer. Known as ‘slurry seal’, this method preserves the streets with pavements that are mostly in good condition without structural failures. The combined treatment is at least 10 times more cost effective than traditional reconstruction methods and can extend pavement life an average of 5 to 10 years.

Slurry Seal is a mixture of emulsified asphalt (oil), water, fine crushed rock, and sand.  It is a surface applied treatment designed to extend the life of existing streets in two ways.  It helps to maintain the integrity of the roadway by filling surface cracks and voids.  By replenishing roadway surface oils, it also acts as a water repellent cap, shedding water into the gutters and preventing water damage to the subsurface of the street.

Slurry Seal is only used for preventive maintenance and is designed to extend the life of a pavement.  It will not improve the ride quality of a street.

The Construction Process

Application of Slurry Seal is a two-step process.  First, surface cracks are filled and surface patching is done.  There is no parking on the affected street on the day this takes place.  Notices will be posted beforehand.  Several days after the crack sealing and surface patching, the Slurry Seal is applied.  Streets will be closed to both parking and driving during the application although limited driving will be allowed in case of emergency.  Normal driving and parking will be allowed after the contractor removes the ‘No Parking’ signs at the end of the working day.  Slurry Seal requires only a few hours to dry before traffic can drive over it, but it takes 24 to 48 hours to cure completely.  During the first few weeks after the slurry seal application, residents should avoid excessive steering of their vehicle while it is standing still, or starting or stopping quickly as this may cause tire tracks and scuff marks on the surface.

Asphalt Grind & Overlay Methods

Comprehensive road rehabilitation encompasses overlay methods that apply structural enhancements to the asphalt layer and improve load-carrying capability. The Town usually applies 1.5 to 3 inches of asphalt concrete overlays to streets with pavements that are in fair condition with mild to moderate levels of base failure.  Before the application of asphalt overlays, roto-milling removes approximately 1 ½ to 2 inches of existing pavement in order for new asphalt pavement materials to fully adhere to the surface. Preparatory work such as asphalt patching, edge milling and utility adjustments will be completed prior to any overlay work. These overlay treatments are at least 3 times more cost effective than traditional reconstruction method and can extend the service life of a pavement 10 to 20 years.

Residents are encouraged to keep curbs clean and free of leaves and other debris to prevent clogs. This includes using acceptable materials in parking strip construction.