New chip seal alternative for bike lanes

In the spring of 2019, ACHD pavement management became aware of an all-in-one machine that could provide the equivalent of a chip seal treatment to bike lanes and stem roads—the portion of road leading into a cul-de-sac.

The Ada County Highway District hired Asphalt Systems, Inc. (ASI) from Tucson, Arizona to demonstrate their small aggregate friction seal machine and in the summer of 2019, a demo project began. Approximately twelve stem roads were friction sealed, as was the bike lane on Emerald Street between Cloverdale Road and Maple Grove Road.

Unfortunately, the stem road experiment was not successful. The machine was not able to apply the friction seal to the tapers (the curved portion of road leading into a cul-de-sac). Consequently, the results looked uneven.

But the bike lane demo was hugely successful. The friction seal was able to fill in the grooves left behind from chip sealing, and the very small aggregate used in the formula created a smoother ride for cyclists. Sealed bike lanes also meant that the Highway District was also happy, as the whole purpose of chip sealing is to protect and extend the life of asphalt.

The demonstration was presented to ACHD’s Bicycle Advisory Committee, who also appreciated the treatment.

It was determined that ACHD would contract with ASI every two years to friction seal highly used, priority bike lanes in the chip seal zones which had been recently treated with a chip seal. ASI will return to Ada County next year to perform their first treatment in Chip Seal Zones 1, 2, and 6.

Friction sealing costs approximately $3.50/square yard—quite a bit cheaper than the slurry seal treatment and microseal treatment, which each run about $5/square yard. Next year’s friction seal project is expected to cost approximately $150,000.