§ 71.123 MOBILITY STANDARDS.

   (A)   General.

      (1)   As all three study intersections are under ODOT jurisdiction, the 1999 Oregon Highway Plan (1999 Oregon Highway Plan, Oregon Dept. of Transportation, amended January 2006) (OHP) sets out planning mobility standards based on functional classification, posted speed limit, presence of highway segment designations and location relative to urban growth boundaries, which employ v/c ratios rather than LOS. Selected relevant mobility standards from the OHP, Policy IF, that are to be applied to the study intersections along Oregon 82 and Imnaha Highway can be seen in the following table. It should be noted that at unsignalized intersections, the mobility standards from Table 2 are to be applied only to movements that are not required to stop or yield right-of-way. For movements that must stop or yield right of way, the mobility standard for district highways/local interest roads is to be applied, regardless of the actual highway classification.

      (2)   While the planning mobility standards from the OHP are used for deficiency identification purposes, a different set of mobility standards from ODOT’s Highway Design Manual (HDM) (Highway Design Manual, Oregon Department of Transportation - 2003 English) are used for design. Therefore, future needs are determined by comparing operations to the OHP mobility standards, while the adequacies of proposed improvements are determined by comparing operations to the HDM standards. The HDM mobility standards have also been included in the following table 2.

      (3)   Because Oregon 82 is designated as a statewide highway and both study intersections at Imnaha Highway and McCully Avenue are within the Special Transportation Area (STA) designation, the v/c ratio requirement for unstopped movements at these intersections is 0.90 (for both OHP and HDM standards) or lower during the 30 HV. Imnaha Highway is designated as a district highway, with the study intersection at College Street being in a zone posted for 30 mph (with a 20 mph school zone to the east). Therefore, the v/c ratio requirement for unstopped movements at this intersection will also be 0.90 or lower during the 30 HV for planning purposes (OHP), but will be 0.80 or lower for design applications (HDM). Stopped movements at all study intersections will be subject to the mobility standard for district highways/local interest roads.

 

Selected Mobility Standards
Maximum Volume to Capacity Ratios Inside Urban Growth Boundary, Non-MPO
Highway Category	Inside a Special Transportation Area (STA)		Outside a Special Transportation Area (STA) with Speed < 35 mph
	1999 Oregon Highway Plan	2003 Highway Design Manual	1999 Oregon Highway Plan	2003 Highway Design Manual
Statewide highways (non-freight route)	0.90	0.90	-	-
District highway/ local interest roads	0.95	0.95	0.90	0.80

 

   (B)   Operational analysis results.

      (1)   Each study intersection was analyzed using the traffic volumes shown in the “Existing and Future AM/PM Peak Hour Traffic Volumes” map and the existing lane configurations and traffic controls. No modifications to these intersections were assumed to occur in the future. The operational analysis was performed using the Synchro software program, which employs the Highway Capacity Manual (2000 Highway Capacity Manual, Transportation Research Board, Washington D.C., 2000) methodology. The results of this analysis are shown in the following tables for conditions under existing (2008) and future (2030) traffic volumes.

      (2)   As shown in following tables, under existing conditions the PM peak hour experiences more congestion than the AM peak hour, with the intersection on Oregon 82 at Imnaha Highway being the most congested. However, all study intersections operate well and are in compliance with adopted mobility standards.

Intersection Operations - AM PEAK HOUR
Intersection	OHP Mobility Standard (v/c ratio)	v/c ratio	LOS	delay (sec)
		2008 Existing Conditions
Oregon 82 @ Imnaha Highway	0.90	0.12	B	11.0
Oregon 82 @ McCully Avenue	0.90	0.02	B	10.4
Imnaha Hwy @ College Street	0.90	0.01	A	9.4
		2030 Future Conditions
Oregon 82 @ Imnaha Highway	0.90	0.21	B	13.4
Oregon 82 @ McCully Avenue	0.90	0.05	B	11.6
Imnaha Hwy @ College Street	0.90	0.02	A	9.8
NOTES TO TABLE: Operations are only shown for stop-controlled movements, as they are the critical movements in all cases.

 

      (3)   While traffic volumes will have increased by approximately 55% by the year 2030, adequate operating conditions will continue to be provided at the study intersections, with no further improvements required to comply with ODOT’s mobility standards. Again, the intersection on Oregon 82 at Imnaha Highway will be the most heavily congested intersection.

Intersection Operations - PM PEAK HOUR
Intersection	OHP Mobility Standard (v/c ratio)	v/c ratio	LOS	delay (sec)
		2008 Existing Conditions
Oregon 82 @ Imnaha Highway	0.90	0.31	C	18.9
Oregon 82 @ McCully Avenue	0.90	0.10	B	13.3
Imnaha Hwy @ College Street	0.90	0.03	B	10.2
		2030 Future Conditions
Oregon 82 @ Imnaha Highway	0.90	0.78	F	56.3
Oregon 82 @ McCully Avenue	0.90	0.22	C	19.1
Imnaha Hwy @ College Street	0.90	0.06	B	11.1
NOTES TO TABLE: Operations are only shown for stop-controlled movements, as they are the critical movements in all cases.

 

      (4)   Although it will comply with ODOT’s mobility standards, the delays experienced on the stop-controlled side-streets of the Oregon 82 at Imnaha Highway intersections will be nearly one minute long per vehicle on average, resulting in a level of service F rating. Traffic volumes on the east-west approaches of Imnaha Highway and Wallowa Avenue would be too low to warrant the installation of a traffic signal (according to ODOT Preliminary Signal Warrants for 2030 condition) and construction of a roundabout would have significant right of way impacts, potentially requiring the purchase of all properties adjacent to the intersection. The installation of a separate westbound to northbound right turn lane would provide some benefits (improved to LOS E with 49.5 seconds of delay), but is also likely to require significant impacts to the property in the northeast quadrant of the intersection.

      (5)   Alternatively, if the existing intersection were converted from two-way stop-control to all-way stop-control, all approaches would comply with ODOT’s mobility standards from the HDM. As an added benefit, the new stop-control on the northbound and southbound highway approaches would facilitate bicycle and pedestrian crossings. However, while the side-street operations would be significantly improved, the north-south highway approaches along Oregon 82, which previously experienced almost no delay, would be significantly degraded to the point where the critical v/c ratio would actually be higher than under no-build conditions (from 0.78 to 0.82). The following table shows the v/c ratios, levels of service and delay anticipated to occur on each approach under all-way stop-control.

 

Oregon 82 at Imnaha Highway Operations under All-Way Stop-Control (2030 PM PEAK HOUR)
Intersection Approach	v/c ratio	LOS	delay (sec)
Northbound	0.67	C	18.6
Southbound	0.82	D	26.9
Eastbound	0.26	B	11.9
Westbound	0.40	B	13.2

 

      (6)   Again, it should be recognized that no improvements to the Oregon 82 at Imnaha Highway intersection are necessary to comply with ODOT’s adopted mobility standards. Because the installation of all-way stop-control would introduce trade-offs in transportation operations, improving side-street, bicycle and pedestrian movements at the expense of highway through traffic movement, the appropriate treatment of this intersection should be discussed between ODOT and the city, with prioritization of traffic movement reflecting statewide, regional and local needs.

      (7)   The need for advanced warning signing for motorists traveling along Oregon 82 should also be considered if all-way stop-control is to be implemented. Such signing may improve driver awareness, as this would be the only required stop for several miles in either direction. However, the roadside environment in this area, including angled parking, striped crosswalks and zero building setbacks, should already convey to motorists that stopping may be necessary.

      (8)   Under existing conditions, vehicle queue lengths at study intersections are relatively low, ranging from two to four vehicles in length during peak periods (noted during observations in the field). With existing block lengths of approximately 300 feet, queue spillback into adjacent intersections is rare.

      (9)   Future vehicle queue lengths in the year 2030 were calculated through a simulation analysis using the SimTraffic software program. The results showed that vehicle queues will continue to be low, with the highest queues found at the Oregon 82/Imnaha Highway intersection of less than 200 feet, which would still fit within the existing block lengths.

      (10)   If all-way stop-control were installed at the Oregon 82/Imnaha Highway intersection, the queue lengths on the eastbound and westbound approaches would not be significantly different, but the northbound and southbound approaches, which previously were not required to stop, would experience much longer queues. However, it was estimated that these queues would be approximately 175 feet long in the northbound direction and 275 feet long in the southbound direction, which would still fit within the existing block lengths.

(Ord. passed 6- -2009)