9th Avenue on either side of Balboa with new Flex Seal treatment
Darker color with Flex Seal but some residents describe surface as bumpier
The San Francisco Department of Public Works (DPW) is experimenting with a new street paving treatment that re-uses old tires and leaves surfaces smooth and, reportedly, safer. Flex Seal, according to its manufacturer, is a "revolutionary asphalt emulsion" that mixes the recycled tires with asphalt, polymers, and other agents. The new product is less expensive and helps stretch DPW's under-financed street repair budget to repave many more blocks. In San Francisco Flex Seal has been tested primarily on dozens of local, neighborhood blocks that receive less wear and tear. These blocks appear much darker than others with regular asphalt applications, and the surfaces are expected to retain their color longer. The Flex Seal blocks have a more textured feel than just-applied asphalt, and a few residents think the surface is bumpier than with asphalt.
The lower costs of the treatment are persuasive, but Flex Seal paving has won high marks from public works departments in other California cities for the product's effectiveness as well. In Los Angeles and San Clemente, street repair directors have found that the product yields significant protection from sun and water damage. The rubberized material inhibits oxidation of oils that give pavement surfaces their flexibility and deters the development of cracks. Keeping water from entering into cracks and seeping into the street sub-base is essential to preserving the integrity of the surface and preventing further damage. The pavement protection has a five-year life cycle, according to the manufacturer's marketing promotion. Although San Francisco is currently testing the treatment only on less-used streets, two other types of Flex Seal have been developed for use on busier collector streets and on high-volume traffic corridors.
The verdict is out on Flex Seal for use in San Francisco, but the treatment does seem to yield additional benefits:
- traffic on road surfaces with the new seal are reportedly less noisy
- the dark surface yields a greater contrast with lane striping, possibly resulting in greater safety
- surfaces seem to give tires a better grip, even when wet
- 100 discarded tires are re-used for each mile of product application, putting a slight dent in the 273 million tires that get tossed every year
The San Francisco Bicycle Coalition is encouraging its members to take test rides on streets with the new treatment to determine rideability and degree of tire grip when the surfaces are wet. Check the SFBC Good Roads page for a list of streets. We will report further on the surfaces and provide a more extensive list of city blocks with the Flex Seal treatment in the days ahead.