Figure 11 portrays the city’s current street system. Figure 11 classifies city streets according to the Washington State Department of Transportation (WSDOT) Roadway Functional Classification System. The WSDOT and the Federal Highway Administration define four functional street classification categories that are applicable to urbanized areas. The four classes of streets are principal arterial, minor arterial, collector arterial, and access streets. These classes recognize a transition in street use from strictly providing access to property to regional mobility. They are grouped according to their traffic volumes, geometric characteristics, and the type of land use they serve. Traffic volumes on city streets can be measured by counting Average Daily Traffic (ADT). Since this comprehensive plan does not anticipate any changes to the current functional classifications, Figure 11 represents both the existing and future street network of public streets.
The functional street classification categories are described below.
Principal Arterials. These provide for traffic movements into, out of, and through Prosser. Many of the trips using principal arterials have neither their origin nor their destination within Prosser, but are generated by the surrounding areas within Benton County. Principal arterials carry the highest traffic volumes and serve the longest trips. The traffic movement function is emphasized at the expense of convenient access to adjacent land uses. Regional and inter-city bus routes are generally concentrated on the principal arterials, as well as support facilities such as transit centers, and park- and ride-lots. The principal arterial classification is further subdivided into: 1) interstate freeways, 2) other freeways and expressways and 3) other principal arterials without strict access control..
Minor Arterials. Minor arterials connect with, and augment, the principal arterials, and serve intra-city as well as some through-trips. A minor arterial provides more access to abutting land uses than does a principal arterial. Minor arterials also serve local and intra-community bus routes and business centers.
Collector Streets. These provide for movement within neighborhoods and funnel neighborhood trips onto the principal- and minor-arterial street system. Collectors typically carry moderate traffic volumes, relatively shorter trips than the arterials, and little through-traffic. In the downtown, collector streets may include the street grid which forms a logical entity for traffic circulation. Local bus routes may use collector streets for passenger pick-up in residential areas.
Minor Collectors. Minor collectors are two-lane streets that collect (or distribute) traffic within a neighborhood and provide the connection to a minor or principal arterial. Minor collectors serve neighborhood traffic, and also provide access to abutting land uses. They do not carry much through-traffic, and are designated to be compatible with residential neighborhoods and local commercial areas.
Major Collectors (also considered under the land use policies as a “secondary arterial”). Major collectors provide connections between a principal arterial and concentrations of residential and commercial activities. The amount of through- traffic is less, and there is more service to abutting land uses. Traffic flow is given preference over lesser streets.
Figure 11: Map of Street System and Classifications
The following table provides an inventory of state-owned transportation facilities in the City of Prosser. HSS is an acronym for Highways of Statewide Significance. “1” is a designator for Rural Interstate, “6” is a designator for Rural Collector, and “7” is a designator for Rural Minor Arterial.
Table 12: Inventory of State Owned Transportation Facilities
SR MP Enter UGA
HSS or Non-
The level of service (LOS) is an estimate of the quality and efficient performance of transportation facilities in a community. LOS standards are provided by the Transportation Research Board's Highway Capacity Manual. The Manual's LOS system measures the degree of traffic congestion and delay using the letter rating "A" for the least amount of congestion, to the letter "F" for the most amount of congestion. LOS standards are most often described by travel times, freedom to maneuver, traffic interruptions, comfort, convenience, and safety.
Communities are allowed to decide what level of congestion is tolerable. The following letter ratings are used to determine LOS standards:
Level of Service A. Low volumes, high speeds, and no delays. Freedom to select desired speeds (within designated speed limits) and to maneuver within the traffic stream is extremely high. Nearly all drivers find freedom of operation and there is seldom more than one vehicle in the queue.
Level of Service B. Zone of stable flow. Drivers still have reasonable freedom to select their speed(within designated speed limits). However, some drivers begin to consider delay and inconvenience and occasionally there is more than one vehicle in the queue.
Level of Service C. Still in the zone of stable flow, but speeds and maneuverability are more closely controlled by the higher volumes. The selection of speed is now affected by the presence of others, and maneuvering within the traffic stream requires vigilance on the part of the driver. Many times there is more than one vehicle in the queue and most drivers feel restricted, but not objectionably so.
Level of Service D. Approaches unstable flow. Speed and freedom to maneuver are severely restricted. Small increases in traffic flow will generally cause operational problems at this level. Often there is more than one vehicle in the queue and drivers feel quite restricted.
Level of Service E. Represents operating conditions at or near the capacity of the highway. Low speeds. Freedom to maneuver within the traffic stream is extremely difficult. Any incident can be expected to produce a serious breakdown with extensive queuing. There is almost always more than one vehicle in the queue.
Level of Service F. Describes forced flow operation at very low speeds, where volumes are above theoretical capacity. Operations are characterized by stopand-go traffic. Vehicles may progress at reasonable speeds for several hundred feet or more, then be required to stop in a cyclic fashion. Long delays result. Forced flow which represents an intersection failure condition that is caused by geometric and/or operational constraints external to the intersection.
The uniform urban- and rural-area level-of-service standards for Prosser, and all of Benton County, are determined by the Benton-Franklin Regional Council in its Regional Transportation Plan. A uniform LOS of "D" is the acceptable urban areas LOS for Prosser's preparation of its Comprehensive Plan under GMA. However, at the discretion of each jurisdiction, a higher or lower LOS may be used on selected portions of the urban transportation network. The City of Prosser has chosen LOS "C" as its standard (except for its downtown area where the LOS is set to “D”).
The following tables show LOS standards for non-signalized intersections in Prosser.
Table 13: Level of Service Criteria for non-signalized Intersections
Source: Highway Capacity Manual, Transportation Research Board. The following tables outline general guidelines established by the Washington State Department of Transportation for determining level of service on roads based on average weekday traffic. The tables pertain to two lane roads in urban population centers of less than 150,000 persons. As noted, adding turn lanes significantly increases the capacity of the intersection.
Table 14: Level of Service for Average Weekday Traffic on Two Lane Roads and Streets
Level of Service
Number of Automobiles
0 to 4,000
4,100 to 7,000
7,100 to 9,000
Source: Highway Capacity Manual, Transportation Research Board
Table 15: Level of Service for Average Weekday Traffic with Turn Lanes at Intersections
Level of Service
Number of Automobiles
Source: Highway Capacity Manual, Transportation Research Board.
Road and Street Design Standards
Average Daily Traffic (ADT). The general unit of measure for traffic defined as the total volume during a given time period (in whole days), greater than one day and less than one year, divided by the number of days in that time period.
Design Hourly Volume (DHV). The DHV is the 30th highest hourly volume (30HV) of the future year chosen for design. On the average rural road or arterial, 30HV is about 15 percent at ADT. For urban areas, 30HV is usually between 8 to 12 percent of the ADT.
Ideal Classification System. In an ideal system, streets would be laid out in a rectangular grid with a functionally strict hierarchy, and a sharp differentiation between classifications. Land use patterns, topography constraints and environmental conditions dictate an irregular street system, and the classification system can only achieve a rough approximation of these ideal guidelines.
The higher classified streets handle the highest traffic volumes. Principal arterials account for only 5 to 10 percent of the total highway mileage in an urban area, but carry 40 to 65 percent of the total travel (measured in vehicle miles of travel). Local streets, on the other hand, comprise 65 to 80 percent of the system but carry only 15 to 20 percent of the travel demand. This plan recognizes roadway elements as stipulated in the Washington State design standards for cities and counties. The right of way in all cases must not be less than the total width for all design elements. Definitions for some transportation planning terms are necessary. According to the City and County Design Standards, 1989, published by the WSDOT, the terms are defined as follows:
Clear Zone. The clear zone is that roadside border area starting at the edge of the traveled land that is available for safe use by errant vehicles. The available clear zone is the distance measured in feet normal to the highway beginning at the edge of the traveled land to the closest part of any fixed object or nontraversable objects.
Jurisdiction. I-82 is under the jurisdiction of the U.S. Department of Transportation. SR 221 and SR 22 are under the jurisdiction of the State of Washington. All other streets within the City boundaries are under the jurisdiction of the City of Prosser. Streets within the proposed urban growth areas are under the jurisdiction of Benton County until these areas are annexed into the jurisdiction of the City.
Road and Street Construction Standards
Prosser's City Engineer has developed construction standards for Prosser roads and streets, and street curbs and gutters. These construction standards are in accordance with the Standard Specifications for Road, Bridge, and Municipal Construction, published jointly by the Washington State Department of Transportation, and the American Public Works Association. These standards shall guide the determination of adequacy of transportation facilities under policy TC 1.1.
Forecasts of Traffic Volumes
As required by the Growth Management Act (GMA), all forecasting of future traffic volumes in this plan is based on the orderly development of the city as set forth in the Land Use Element.
GMA also requires that LOS standards be regionally coordinated. This coordination occurs locally through the Benton-Franklin Council of Governments (BFCG), which is the Regional Transportation Planning Organization (RTPO) for the bi-county area.
There have been several studies of traffic in the City of Prosser over the last decade. The conclusions of these studies have suggested that progressively portrayed there could be a worsening of traffic conditions. Some of these forecasts, notably those prepared by the Benton Franklin Council of Governments, indicate that there will be significant reductions in levels of service on several city streets. However, these estimates of future activity would occur only with significantly greater increases in traffic than what available traffic counts indicate is occurring, and what would be required to accommodate the population growth that the land use plan would generate. Nonetheless, these forecasts are described below to demonstrate that the planning process has considered all available information, especially information developed by the regional transportation planning process. However, as discussed below many of these forecasts are unlikely to occur and should be considered a “worst-case” scenario of traffic conditions.
A 1996 comprehensive analysis of the City of Prosser Transportation system by Bucher Willis and Radliff, “Prosser Citywide Transportation Study,” concluded that:
“Trend analysis forecasting procedure is appropriate for the City of Prosser. Land use development patterns are expected to be steady and stable. Traffic congestion is not expected to be an important issue. Traffic diversion to alternate routes or time frames are not expected to be significant. Trend analysis forecasting process is expected to provide appropriate projections...”
This 1996 study basically concluded that congestion is generally not a problem in the City of Prosser. In forecasting future traffic, BRW identified six streets where the LOS could reach D or lower by the year 2015:
Wine Country Road South of Nunn Road
Wine Country Road North of Gap Road
6th Street Southeast of Sheridan
7th Street Northwest of Meade Ave.
Bennett Ave. Southwest of 6th Street
Meade Street Southwest of 6th Street
Since this study, improvements have been made to Wine Country Road which addressed the potential deficiencies on Wine Country south of Nunn Road. Deficiencies on Wine Country north of Gap Road (which extends outside the city limits) would be related to potential commercial development in that area and facilities to support such development are addressed by the financial strategy in the Capital Facilities Element that would apply concurrency to future development in the area and require developer financing of needed facilities. The potential deficiencies related to downtown are discussed below. In addition to these needs this study also documented a range of transportation deficiencies in the form of substandard road ways and unsignalized intersections that could pose safety hazards as increasing volumes of traffic use these facilities.
In 2003 a comprehensive-plan update revisited transportation needs on the basis of the then effective 2001-2020 Benton Franklin Regional Transportation Plan (RTP). This Regional Transportation Plan for the Tri-Cities Metropolitan Area & Benton-FranklinWalla Walla RTPO (RTP) describes future congestion problems anticipated on local arterial streets through 2020 and the capacity improvements needed to relieve said congestion while maintaining a LOS C or better. Traffic counts taken on May 2, 2002 reinforced the 2001-2020 RTP’s depiction for the City of Prosser’s traffic conditions. The projection of LOS in the 2001-2020 RTP was based upon a 2% annual growth rate for traffic. The construction of the projects listed in that RTP was anticipated to ensure that an LOS C is maintained through 2023.
Table 16: Projected Traffic Volumes and Level of Service: 2003-2023
Based on 2.0% annual growth rate of traffic volumes
In a more recent update of the Regional Transportation Plan for 2006-2025, the Benton Franklin Council of Governments focused on different streets and concluded “Prosser has some serious congestion problems developing.” Table 17 presents their most recent forecasts as published in the 2006-2025 Regional Transportation Plan, November 2006. While Table 17 is taken directly from the regional transportation plan (Page 8-6), there are no traffic counts or discussion of the forecast methodology supporting these estimates.
Table 17: Project LOS on City Streets from 2006-2025 Regional Plan
6th Street: Wine Country Road to Meade
7th Street: Wine Country To Meade
Bennett: West of 6th Street
Meade Ave.: Dudley to 6th St.
Meade Ave.: 6th Ave. to 7th St.
Wine Country: I-82 (East) to Port
It should be noted that the forecasted congestion indicated on Table 17 is primarily on city streets in the downtown area south of the railroad tracks, while all of the streets on Table 17 are outside of the immediate downtown area or are north of the railroad tracks. This suggests that the more concentrated development in the downtown may create more congestion than other City streets.
Current Traffic Trends
Table 18: Current Benton Franklin Council of Governments Traffic Counts on City Streets
Tables 17 and 18 present an analysis of the available traffic counts for city streets in Prosser. While Table 17 above portrays 6th Street as performing at level of service D in 2005, the actual traffic count on this street from Table 18 shows it performing at a high level of service in 2007. Similarly while Table 17 portrays Bennett west of downtown as being at LOS D in 2005, the only current (2007) traffic count in this on Table 18 area shows Bennett at LOS A (although an earlier count—2002—closer to downtown has Bennett at LOS B). From the available information, the deficient LOS forecasted for some city center streets for 2005 has not occurred.
Table 19 analyzes the limited amount of data that is on Table 18 that identifies change overtime on the downtown Streets. As indicated, these counts show very little increase in traffic overall, although some shift seems to occur between the two parallel streets on Seventh and Sixth (traffic will tend to shift back and forth on these types of parallel streets if traffic volumes increase—such shifting trends to mitigate the potential of LOS dropping on either one of these streets separately). Based on current traffic trends as indicated by the available data it is unlikely that many of the forecasted deficiencies on city center streets will occur as forecasted on Table 17.
Table 19: Trend Analysis of Downtown Street
W of Sheridan Ave
W of Sheridan Ave
Table 20 estimates the rate of annual increase in traffic that would be needed in order to exceed the LOS standards portrayed on Tables 14 and 15. Since all of the streets listed do not have turn lanes, the LOS would be determined initially by the volumes of traffic indicated by Table 14. However since there is sufficient space to add turn lanes on all of these streets, Table 20 also compares the annual increase required for different LOS levels (from Table 15) with turn lanes added. It should be noted that the addition of such lanes could be provided at little expense and would probably not require a capital project.
As noted on Table 20, all of these streets, except for 6th Street, would require rates of growth in excess of 2% in order to pose a LOS problem within the planning period on existing street configurations. Addition of turn lanes would require even higher rates of growth in order to pose capacity issues and the addition of such lanes would raise the rate of increase needed for LOS D to occur on 6th Street would be almost 3%. (Another option to increase capacity on downtown streets would be to signalize the intersections).
This analysis demonstrates that the worst-case estimates of LOS by BFCOG as presented on table 17 are unlikely to occur within the forecast period since the rates of increase required for that forecast are not occurring. Even if higher rates of growth did occur, there are relatively low cost options that could raise the LOS up to acceptable levels. However, since increased downtown congestions would accompany increased downtownbusiness activity, this plan reduces the adopted downtown streets from the “C” adopted for the rest of the City to “D” in order to accommodate the vision of the land use element for a more robust downtown. As indicated on Table 20 traffic volumes would need to increase by almost 4% per year in order for a LOS to drop below the adopted “D” with the streets striped for turn lanes. Since this is a very high rate of growth, it is unlikely that major capital projects will be needed to address downtown congestion in the forecast period. In accord with the land use element, the population growth rate needed to accommodate the population allocation is only 1.56% per year.
The analysis on Tables 19 and 20 suggests that Table 16, which is based on the 2001- 2020 Benton Franklin Regional Transportation Plan (RTP), reflects a forecast of future conditions more accurately than Table 17, and Table 16 shall be used as the traffic forecast for identifying capital improvements in the Capital Facilities Element needed for the transportation system. Table 20 shall be used as a “worst-case” forecast for future reference.
Table 20: Analysis of Future LOS on Downtown Streets
E in 2025
W of Dudley Ave
W of Sheridan Ave
W of Sheridan Ave
Table 18 does portray higher traffic volumes north of the River on Wine Country Road than the rest of the City. Recent improvements on Wine Country were designed to accommodate these higher traffic volumes. However, continued intensification of growth accessing the intersections at the I-82 interchange in the north part of the city will require a major improvement during the planning period.
Impacts of Land Use Plan on State Facilities.
The state freeway and highways through Prosser all appear to be operating at LOS B or better and the state transportation regional plans do not identify any anticipated deficiencies on these systems. The population growth anticipated by the land use plan of 1.56% per year should not add traffic sufficient to create deficiencies on these systems. The exception to this overall picture is that intensification of commercial development in the vicinity of Merlot and Wine Country Road as noted above will create the enhance the intersections serving that interchange.
Regional Transportation Funding
The 2006-2025 Regional Transportation Plan funding plan is presented on the table below.
Table 21: 2006-2025 RTP Project Plan
Wamba Road Improvements - Old Inland Empire Highway to Merlot Road
lighting, bike lane
Kinney Way Sidewalk: Park Avenue to SR 22
Curb and sidewalk
Sheridan Avenue Street Improvements – WCR to Third
Sister Streets (Evans, Ellen, Canyon, Sadie, Anna, Alice, Margaret, Lillian, and Florence)
One of the more significant requirements of the GMA is that, if a proposed development will cause the LOS of a transportation facility to decline below the adopted standard, then the proposed development cannot be approved for construction unless transportation improvements or strategies to accommodate the impact of development are made concurrent with the development. Such development and improvements should additionally be anticipated in the Comprehensive Plan.
Improvements made in recent years to Wine Country Road have addressed immediate congestion issues on the major roadway through the City. While traffic forecasts in excess of current population growth rates do not identify significant problems on many roadways, roadway configuration and below standard construction can create significant hazards in specific areas especially in the downtown area and at unsignalized intersections, as traffic volumes increase. Development of alternative routes, such as Wamba Road and Kinney Way, should aid circulation patterns and tend to reduce potential congestion on the major collectors.
Intensive development in specific areas , such as commercial development near freeway intersections or near rail crossings, may generate traffic in excess of these generalized forecasts creating hazards or congested conditions in these locations. Traffic studies should be completed for any significant development to ensure traffic can be accommodated on the existing system without creating localized congestion or traffic hazards.
The planned improvements to the City’s circulation system are described in the Capital Facilities Element.