How Ultimate Capacity Works

Level of Service Standards

  • The minimum level-of-service standards for county arterials are established in the transportation element of the county comprehensive plan and are set forth in SCC 30.66B.101 and SCC 30.66B.102 (see below).  The determination of whether or not an arterial unit meets the adopted level-of-service standards is as follows:
  • First, if the average daily trips (ADT) on an arterial does not exceed the threshold identified in SCC 30.66B.101, the arterial unit meets the county s standard.
  • As shown below in italic font, once a road is designated as ultimate capacity a higher ADT threshold is established.
  • For roads not designated as ultimate capacity the ADT thresholds are low, and only arterials with relatively low volumes will meet the standard.
  • For roads designated as ultimate capacity the thresholds are high, and are intended to be difficult, but not impossible, to exceed.
30.66B.101: Transportation Level of Service Standard: Average Daily Trip (ADT) Thresholds
Thresholds Measured as
Number of
Average Daily Trips (ADT)
Road Not Designated as
Ultimate Capacity
Road Designated as
Ultimate Capacity
 Number of Lanes  Rural Arterial Unit Urban Arterial Unit   Rural Arterial Unit Urban Arterial Unit 
 2  4,000  7,000  18,000  22,000
 3  5,000  9,000  27,000  33,000
 4 7,000   12,000  36,000  44,000
 5  n/a  15,000  45,000  55,000
 6  n/a
 16,000  54,000  66,000
 7  n/a
 21,000  63,000  77,000

  • If the ADT on an arterial unit exceeds the threshold identified in SCC 30.66B.101, the average travel speed is evaluated. If the average travel speed on the arterial unit falls below the appropriate threshold identified in SCC 30.66B.102, then the level of service on the arterial unit does not meet the county's standard.
  • It is expected that for roads designated as ultimate capacity, once the ADT thresholds are exceeded, they will almost certainly fail the average travel speed test.
30.66B.102: Transportation Level of Service Standards: Average Travel Speed
 Rural/Urban Arterial Unit Classification  Transit Compatibility (1) and Qualifying Public Services (2)  Average Travel Speed Standard
 Rural  No  C(3)
 Rural  Yes  D(3)
 Urban  No  E(4)
 Urban  Yes  5 miles per hour less than E(5)

Ultimate Capacity Provisions of Ordinance 05-092

The 2005 amendments to Chapter 30.66B SCC adopted criteria that Public Works uses to make recommendations to the county council for whether or not certain arterials should be designated as “ultimate capacity.”

  • Initiated by a recommendation from the Public Works Director
    • upon completion of an engineer’s report, and
    • based on criteria in code and DPW rules
  • Ultimate capacity is a County Council determination
    • by motion following a public hearing,
    • when excessive expenditure of public funds would not be warranted for making further improvements,
    • when arterial is designated ultimate capacity, a different LOS standard would apply, which would effectively allow much reduced travel speeds
  • Criteria for DPW Recommendation and Council Designation
    • either road is totally improved consistent with long-range plan, or
    • road is partially improved but certain constraints preclude additional cost effective improvements
  • If road is only partially improved, then
    • number of general-purpose travel lanes (excluding turn lanes) is consistent with the adopted transportation element,
    • adequate provisions are made to accommodate pedestrian and bicycle demand, and
    • if the source of delay is another agency’s facility, then the approach to that facility is totally improved consistent with long-range plan
  • Developments impacting ultimate-capacity arterials would be required to:
    • provide access management and circulation provisions, and either
      • provide transportation demand management (TDM), or
      • meet the criteria for transit compatibility.
  • Designation by Council to include a commitment by the County to
    • complete any known improvements needed to address safety issues,
    • complete an access management and circulation plan, and
    • transportation system management (TSM) actions, access management improvements, and/or transportation demand management (TDM) actions for the purpose of improving efficiency, preserving roadway capacity, and improving operations

“TSM” is the acronym for “transportation systems management” and includes the “high tech” signal timing, coordination, and monitoring that we have in these corridors and continue to improve.

Access Management can increase roadway capacity by 20 to 40 percent through limiting vehicle conflicts at driveways and other points of access.  Access Management may include both land-use actions (e.g., requirements for shared driveways and parking) and minor capital improvements (e.g., center curbing). 

“TDM” is the acronym for “transportation demand management.  TDM responds to the long-term need to maintain mobility while reducing vehicle trips and includes programs that provide incentives for sharing rides and using transit (e.g., “developer TDM” and “commute trip reduction”).