Taking Multiple Approaches to Preserving the Streets of Idaho

A robust preservation program goes a long way.  More than 2,500 lane miles were treated over 6 years to extend the life of Boise’s urban and residential roads using chip seal and preservation. 

  1. 85% savings vs Mill and Fill per square yard
  2. More than 2,500 lane miles were treated in 6 years
  3. 20 point improvement in PCI ratings since the program began


The city of Boise, Idaho has utilized a Chip Seal program since 1995 to maintain their roads, and PCI ratings. Every nine years, all arterial, collector, and residential roads were treated with a chip seal to extend the life of the paved surfaces.

Network Approach

The arterial and collector roads in Ada County, Idaho were seeing a decline in their PCI ratings as their nine-year cycle for Chip Sealing program was becoming less effective. A new program needed to be enacted that would not see the same rate of deterioration as previous programs. While Ada County routinely applied Chip Seal treatments to all their roads, chip seal was not ideal for downtown areas and cul de sacs could not be treated.

Our Preventative Maintenance Strategy drives the high PCI ratings. Our entire team prides themselves on the great effort in maintaining our road infrastructure, recognized as the “Best Roads in the Northwest” for the past 4 years.

Lloyd Carnegie
Manager, ACHD Maintenance Department


In 2012, ACHD executed an aggressive six year cycle to increase the frequency of arterials and collectors getting chipped. Crack Sealing was added to the Chip Seal program for all roadways prior to chip sealing, then followed by a Fog Seal to cover and seal the chips. It was determined downtown areas would not be Chip Sealed, and Microsurfacing was implemented due to its rapid cure time, allowing traffic to resume its normal flow without causing a large disruption to the area. A slurry seal was used to treat cul de sacs, allowing a slower cure time to properly seal the pavement. This aggressive chip seal program has maintained their overall PCI to an Excellent/Very Good rating.

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  • Network Condition
  • Preventive Maintenance Zones
  • Chip Seal Process
  • Fog Seal Process