Tuesday, November 16, 2010

City Smooths Streets with Recycled Tire Product, Gets Cost Savings & Paves More Blocks

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.


  1. I think this must be what they just did on the street to the north of Espirit Park (AKA Decom Park). 19th St from Indiana St to Tennessee St.

  2. What do you think, roymeo? How's it look and ride?

  3. Awesome. Even if it is a little bumpier (and I have no idea whether it is), it'll be worth it for all the tyres it saves from landfill. If the cost benefits lead to more money for bike facilities, that's a win too.

  4. If it is slightly bumpier, thats not a bad thing. It slows people down. The effect of a gravel road, but smooth for cyclists and wheelchairs? Sounds perfect.

  5. It feels pretty much like fresh pavement, I'm not noticing a significant difference in how smooth it is...or maybe it's just that I notice no fall in feeling since it's applied to a street that had cracks (some tar-filled) etc.

    Also spotted on Illinois St from 20th to 25th St, with a spur out to 3rd St on 24th St. (Though they didn't do it down the southbound lane which has useless train-tracks in it.)

    And also spotted on 15th St, crossing DeHaro St.

    I've ridden on it in wet and dry conditions, and it seems to perform better than the regular smooth asphalt on surrounding streets for stopping and skidding. Time will tell whether it actually wears better--I can see the case for it being better if it wears a bit more like car tires and doesn't get slick and smooth as the asphalt can.

  6. Thanks, roymeo, for the comprehensive report.