Congestion Management Monitoring
Report Summary
2000

Congestion Management Network

The CMS corridors consist of regional facilities that are currently or are likely to become congested. They form a subset of the Vancouver/Clark County Regional Transportation System. The congestion management network is made up of twenty-nine corridors. The endpoints for each corridor represent locations where the characteristics of the corridor changes significantly. 

Where appropriate, individual corridors are made up for more than one transportation facility. The multi-facility corridors occur where there is more than one route within a corridor serving the same function. A corridor approach that incorporates parallel routes and transit services provides a regional orientation and responds to the multimodal and alternative travel themes of the Federal Transportation Act. Although group by corridors, data is reported for individual facilities.

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Corridor Congestion Ratio

The corridor congestion ratio is an aggregation of the volume/capacity (V/C) ratios for the individual segments that make up a facility within a corridor. For each segment in a corridor, the V/C ratio, vehicle miles traveled (VMT), and VMT-weighted V/C ratio (the product of the V/C ratio and VMT) for the peak hour are calculated. The CCR is the sum of the weighted link ratios. It is intended to show the overall V/C ratio for the length of a corridor instead of a single location on the facility.

The PM periods show congestion along major facilities such as I-5, I-205, SR-14, SR-500/Fourth Plain, Burton/18th Street, 164th Avenue, Ward Road, Mill Plain-East, SR-503-South, and SR-502. Planned improvements along Ward Road and Burton Road are likely to reduce the congestion index in these corridors.

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Speed as Percent of Speed Limit

The City of Vancouver and Clark County collect travel time for concurrency purposes along many congestion management corridors. RTC collects additional travel time data in congestion management corridors that were not part of the concurrency data collection effort. The methodology for collecting the travel time data was consistent among agencies. Travel speed was computed by utilizing the travel time and distance information. Speed was then converted to a percent of posted speed for each of the congestion management corridors.

In general, facilities with at-grade intersections, display lower speed percentages. The speed percentages for the freeway facilities are close to 100% of the posted speed limit. The eastern portion of Mill Plain and southern portion of 164th Avenue displays the lowest percentages of speed in the PM period.

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Auto Vehicle Occupancy

Auto vehicle occupancy is calculated by counting passenger cars at a given location and the number of people in each vehicle. The number of people divided by the number of cars is the auto vehicle occupancy for that location. Auto vehicle occupancy information has been collected at twenty locations (15 in 1999 and 5 in 2000) throughout the Clark County area. Data was collected for freeways and arterials during the AM, PM, and midday time periods.

In the PM peak, SR-14, I-205 and I-5 south of Main Street have the lowest average vehicle occupancy rates (1.12 to 1.18). The two east/west arterials, Fourth Plain and Mill Plain have the highest average vehicle occupancy rates possibly due to a higher percentage of non-commute trips. The PM time period has a higher auto occupancy rate, likely due to a greater percentage of discretionary trips such as shopping where drive alone trips are less prominent.

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Truck Percentage

Traffic counts collected for the CMS include several locations that also classify vehicles according to the number of axles. Trucks are defined as vehicles with more than two axles, such as typical tractor/trailer rigs, travelling on the roadway during the peak period. This is a measure of trucks as a percentage of all vehicles travelling on the roadway.

Overall, the freeway facilities and SR-501 accessing the Port of Vancouver display the highest percentage of truck volumes during the PM peak period. The exception to this is on SR-500, which has truck percentages similar to major arterials, such as Andresen Road and 164th Avenue. SR-14, I-5 and I-205 corridors have truck percentages of 5% or higher. Fourth Plain Boulevard/SR-501 from I-5 to the Port of Vancouver has the highest percentage at 17.9% of PM peak vehicle volumes. (Count was taken prior to the completion of the Mill Plain Extension). I-5 North and I-205 Central also have significant truck percentages (13.8% and 10.3%).

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Transit Seat Capacity Used

The percent of transit seat capacity used is calculated by identifying total bus ridership for a segment within a corridor and calculating the total bus capacity at the same location based on transit vehicle size and service frequency. Transit capacity used includes all transit riders divided by the transit capacity at the peak location.

During the PM period I-5 south of 134th St., I-205 south of SR-500, and SR-14 west of 164th, and Fourth Plain west of Andresen utilize more than 64% of the available seats. Other corridors without express service such as Highway 99, Hazel Dell Avenue, 78th Street, and Andresen Road south of SR-500 corridors utilize more than 45% of the available seats in the PM.

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This report was prepared by: