Roadway System Needs
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Technical Appendix B-1 Washington County 2020 Transportation Plan Page 1 of 10 Roadway System Needs The year 2020 transportation system deficiencies and needs in Washington County were evaluated based on selected performance measures. The 2020 travel forecasts considered the Regional Transportation Plan (priority scenario) as well as no-build scenario (including committed projects). The following section describes the analytical process and motor vehicles system results. Separate approaches were taken for evaluating urban and rural roadways to better address the characteristics of each type of facility. Performance Analysis in Urban Area Planning performance measures for the roadway system in the urban area include peak period travel demand, mobility, connectivity and accessibility. These performance measures were combined to refine the initial 2020 travel demand model forecasts using a three-tiered analysis. These measures represent a new paradigm for assessing roadway and highway travel performance for Washington County. The previous plan process (1985) used only the first step as described below. Since that time, further research in system performance has provided a broader array of planning tools. Step 1: Demand vs. Capacity — Demand to capacity (D/C) ratios1 were evaluated on roadway segments and conditions where the demand to capacity ratio exceeded 1.0 were identified. Model roadway networks are coded based on the general speed and throughput characteristics of similar facilities throughout the county. See the attached Committed System - Motor Vehicle Performance Deficiencies map (B-1). Step 2: Arterial Congested Speeds — The D/C ratio is taken from the above step, then further refined to consider specific traffic signal density and system coordination along the arterial segments in the county. Signal density (number of traffic signal per mile) has a significant influence on the average travel speeds, especially during peak periods. Urban Street Level of Service Criteria Typical free-flow 50 mph 40 mph 35 mph 30 mph speed Level of Service Average Travel Speeds (mph) A >42 >35 >30 >25 B >34-42 >28-35 >24-30 >19-25 C >27-34 >22-28 >18-24 >13-19 D >21-27 >17-22 >14-18 >9-13 E >16-21 >13-17 >10-14 >7-9 F ≤ 16 ≤ 13 ≤ 10 ≤ 7 Source: Highway Capacity Manual, Chapter 15, Exhibit 15-2, 2000. 1 Demand to capacity ratio is similar to volume to capacity (V/C) ratio. The difference is that in the future, demand is being estimated and therefore the term demand is utilized. For existing conditions, volume refers to the actual traffic on the roadway. While a demand to capacity ratio can exceed 1.0, a volume to capacity ratio would never exceed 1.0. Technical Appendix B-1 Washington County 2020 Transportation Plan Page 2 of 10 Refined travel speed estimates were prepared based on forecasted peak period usage, traffic signal density, presence of signal coordination and free-flow travel speeds on arterial roads. The refined arterial speed calculation was based on Quantifying Congestion (NCHRP Report 398) research2. Future signal density (number of traffic signals per mile) was determined from the existing traffic signal inventory provided by county staff plus assumptions3 regarding new traffic signals that may be constructed with land development. Future traffic signal coordination was determined based on conversations with county staff regarding planned signal system upgrades. The resulting congested speed was related to the definition in the Highway Capacity Manual for Urban Streets4 to determine a facility level of service. Cases where a corridor segment dropped below Level of Service E were flagged for poor or unacceptable performance. Step 3: Intersection Performance — Intersection level data were developed for about 25 intersections in Washington County (based on staff input, for primarily arterial intersections). The 2020 model forecasts at these intersections were adjusted to correct minor calibration errors that may occur compared to current year traffic counts. This refinement step can significantly enhance the accuracy of the model forecasts and the resulting performance assessment. The intersections were selected because they are the most likely pressure points where system capacity could be exceeded. However, there may be other locations that may have capacity deficiencies/needs. Other county arterial intersections were investigated in separate studies for the various city transportation system plan updates. Any needs shown at these locations will be addressed in the county plan update. Capacity needs were identified where D/C ratios exceeded 1.0 or Level of Service (LOS) was at F or worse. The three-step approach was not applied to roadway facilities in the rural area. The influence of traffic signals and mid-block driveways is generally not significant in the rural area. An alternative method was developed to consider roadway terrain and limitation to passing zones, which are more significant to rural travel conditions. 2 Quantifying Congestion: Volumes 1 and 2, National Cooperative Highway Research Program, Report 398, Transportation Research Board, 1997. 3 Future traffic signals were assumed to be added to the existing system within the urban area for the following cases: 1) where two arterial roads intersect, and 2) as in-fill along arterials with bordering commercial or industrial at least one-quarter mile from an arterial or other existing traffic signal. 4 Highway Capacity Manual, Chapter 15 – Urban Streets, Transportation Research Board, 2000. Technical Appendix B-1 Washington County 2020 Transportation Plan Page 3 of 10 Refined Capacity Analysis Process for Urban Area Refinement Step Process /Purpose Threshold (acceptable performance indicator) 1- Link Demand Model volume divided by model D/C less than 1.00. to Capacity capacity. General link performance. 2 - Congested Arterial road performance based D/C Level of service E or better. Speed ratio (Step 1), traffic signal density and control systems, and speed reduction relative to free-flow. 3 - Intersection Arterial intersection average delay for Level of service E or better. Total Conditions all movements. Adjust model control delay less than 80 seconds forecast relative to counts. on average for all movements (source: Highway Capacity Manual 2000). The results of the urban area corridor evaluation are summarized on the next page for the Committed Project and Priority RTP scenarios. The table highlights roadway links that fall below the performance measures. All 37 of the links listed in the table have demand to capacity ratios over 1.00 for the Committed Base scenario (Step 1). The majority of these corridors also have average travel speeds in the peak direction below Level of Service E (Step 2). Cells that were grayed out do not have traffic signals installed or planned within the corridor limits. The node capacity analysis (Step 3) shows that the majority of the corridors also have major intersections that will perform below LOS E during the peak period. Cases where intersection traffic volume data was not readily available for analysis are shown as shaded. An important finding was that, in most cases where data were available, the Step 1 deficiency was confirmed by inadequate conditions based on travel speed and/or intersection LOS. The Priority scenario analysis showed 14 of the 37 links operating below capacity. The other 23 links would be adequate during peak periods with implementation of the additional system projects identified in the Priority scenario program. In a few cases, the corridor speed was the critical indicator instead of link capacity. These included Highway 99W and Cornell Road in sections where traffic signal spacing is very close, and the impact on travel speeds is significant. Technical Appendix B-1 Washington County 2020 Transportation Plan Page 4 of 10 Overview of 2020 Forecasted Corridor Deficiencies for RTP Scenarios No Build Priority Step 1 Step 2 Step 3 Step 1 Step 2 Step 3 East-West Corridors (1) Link Speed Intersection Link Speed Intersection Germantown Road – Cornelius Pass to Kaiser Rd n n Springville Road – 185th Ave to Kaiser Road n n West Union Road – Cornelius Pass to 185th Ave nn n n Cornell Road – 185th Ave to US 26 nn n Cornell Road – 143rd Ave to Saltzman Road nn n US 26 – ORE 217 to Canyon Road n Walker Road – ORE 217 to Stucki Ave nn n Jenkins Road – Murray Blvd to 158th Ave nn Baseline Road – 185th to 231st Ave nn TV Highway – Hocken Ave to Cornelius Pass nn n Highway 8 – Cornelius/Schefflin to Hwy 47 nn n n Farmington Road – Hocken Ave to 185th Ave nn n Allen Boulevard – ORE 217 to Murray Blvd n Hart Road – Hall Blvd to Murray Blvd n Scholls Ferry Road – ORE 217 to 125th Ave nn n Tualatin-Sherwood Road – I-5 to Boones Ferry nn n n Road Tualatin-Sherwood Road – Avery Street to Hwy n 99W Step 1 Step 2 Step 3 Step 1 Step 2 Step 3 North-South Corridors (1) Link Speed Intersection Link Speed Intersection Brookwood Avenue – TV Hwy to Cornell Road n n Cornelius Pass Road – TV Hwy to US 26 nn n Cornelius Pass Road – US 26 to Germantown nn n n Road 185th Avenue – Farmington Road to Springville nn n Road 170th Avenue – Bany Road to Merlo Road n Bethany Boulevard – US 26 to Kaiser Road nn Kaiser Road – Germantown Road to West Union n nn Road Beef Bend Road – Scholls Ferry Road to Elsner nn Road Highway 99W – Bell Road to Durham Road nn n n Highway 99W – Durham Road to ORE 217 nn n nn n Highway 99W – ORE 217 to I-5 n Murray Boulevard – Brockman Road to Jenkins nn n n Road Cedar Hills Boulevard – Hall Blvd to Walker Road n Hall Boulevard – Greenway to Oleson Road nn ORE 217 – Denney Road to BH Hwy n ORE 217 – I-5 to Greenburg Road n Scholls Ferry Road – Denney Road to US 26 nn Interstate 5 – Wilsonville Road to ORE 217 n n Boones Ferry Road – Elligsen Road to Avery nn n Street Baker Road – Westfall Road to Tualatin- n n Sherwood Road Technical Appendix B-1 Washington County 2020 Transportation Plan Page 5 of 10 The major intersections and interchanges were reviewed based on forecasted volumes to identify locations that are expected to exceed planned capacity.