Avimor Development Traffic Impact

With 800+ Avimor homes built and its commercial development in Ada County well underway, users of State Highway 55 and its 8 intersections north from State Highway 44 (State Street) are well aware of increased traffic volume and longer wait times as well as the addition of several traffic signals and turning lanes.

A 2020 analysis of the impact of the Avimor Boise County Development on State Highway 55 corridor identified SH 55 / SH44 (State Street) as a high-volume intersection that was already exceeding Idaho Department of Transportation (ITD) standards for capacity on weekday and Friday p.m. Peak Hours.

The same analysis estimated that by 2025, with 360 single- and 240 multi-family housing units, the Avimor Boise County Development will generate 5,152 daily net new trips on SH 55. By 2030, with 1,600 housing units and 70,000 square feet of commercial space, the estimate is 14,801 daily net new trips. In addition to some traffic mitigation proposed by Avimor, ITD has identified additional improvements it will require of the developer at specific phases of its buildout.

While we believe ITD will enforce its requirements and assign Avimor its appropriate responsibilities to mitigate traffic levels, we believe the resolutions will be high-cost, long and disruptive. Examples include the SH 55 / SH 44 intersection (it is already fully built out so ITD needs to determine its future configuration and/or alternatives) and the SH 55 corridor (a study is recommended to identify both the need and desire for additional lanes in both directions north of SH 44). Traffic congestion in the area will be a problem for the foreseeable future.

Traffic Impact Studies

Fortunately, there is data and analysis to document recent increases and to form reasonable estimates of future traffic volume as Avimor completes its Ada County buildout and moves into Boise County. Avimor partners contracted with Kittelson & Associates to conduct a Transportation Impact Study (TIS) for its Boise County Development.

The Avimor Boise County Development is located in southwestern Boise County just north of the current Avimor Village 1 Development in Ada County. Access for the Development will be from the two existing public street accesses from State Highway 55, Avimor Drive and McLeod Way, as well as two in Boise County: one new access and the use of Pearl Road. The Idaho Transportation Department (ITD, a state agency) will be the primary approval agency in addressing the traffic growth. The Ada County Highway District (ACHD, a countywide independent taxing district) is a commenting agency in recognition that the Development will send traffic into Ada County for employment and services.

The Study analyzed existing 2020 conditions, general regional growth, and the Development’s direct impacts on SH 55 and several connecting roads by 2025, 2030, and 2032 (the scheduled buildout of Avimor’s 3 phases in Boise County). It evaluated 10 intersections, three Avimor access intersections, and 12 roadway segments. (pp. 32-33). It focused on traffic volume during the Weekday a.m. and Weekday p.m. Peak Hours of a typical weekday, as well as the Friday p.m. Peak Hours during the summer months. The Study followed the operating standards of ITD and ACHD and used the methodologies stated in Section 7106.6 of the ACHD Policy Manual. (p. 34)

ACHD Policy Manual

Performance standards for intersections and roadway segments included:

  • Level of Service (LOS), a ranking based on the average delay experienced by drivers. LOS grades range from A (free-flowing traffic, very low delay times) to F (stop and go, high delay times considered unacceptable to most drivers). ITD’s threshold is LOS D or better for all intersections.
  • Volume (number of vehicles) compared to capacity of the road, or V/C. A V/C ratio of 1.0 indicates an intersection is operating at capacity; a ratio higher than 1.0 exceeds the road’s capacity. ITD’s threshold is a V/C ratio of 0.90 or lower for the overall intersections as well as for each lane group. (p. 35)

The report, dated September 2020, documents the findings of the Study and the recommendations for mitigation of deficiencies. The findings show that with each Development phase, the number of intersections and road segments expected to exceed ITD’s acceptable standards increases, as does the number of Peak Hour periods that standards are exceeded. Avimor developers have made some improvements to address increased traffic and plan others, but the Study identified many more that will need to be made to maintain ITD’s standard.

ITD Comments to Boise County

In April 2021, ITD shared with the Avimor Partners its intended response to Boise County Development Services regarding its review of the Avimor Boise County Development TIS. (April 8, 2021 letter re: ITD Development Condition Memo) The letter states that Avimor Boise County is already generating significant site traffic. It also points out that the current signal at the SH 55 / Avimor Drive intersection was permitted as a temporary improvement; the TIS identified that intersection as exceeding standards (0.90 V/C) by 2025 during Friday p.m. Peak Hours, and ITD cannot have a temporary signal operating with poor performance.

ITD will require Avimor to do the following:

  • Mitigate SH 55 / Avimor Drive signal for Friday p.m. Peak Hours during summer months so that the northbound through traffic V/C does not exceed 1.0. Within 1 year of the V/C exceeding 0.9, Avimor must widen SH 55 to a 4-lane section at least 1500 feet north and south of the signal.
  • Additional mitigation around Avimor Drive will be negotiated prior to the final plat of anything beyond 600 residential units in Boise County Areas 2 and 3 (to be served by the proposed new access point and by Pearl Road).
  • Limit McCleod Way to right-in right-out and construct an underpass when monitoring determines left movements fail.
  • Construct north- and southbound right and left turn lanes when the new Avimor access point is built in Boise County.
  • Construct a northbound left turn lane at the SH 55 / Pearl Road intersection prior to any building occupancy in Area 3.