Congestion Management Monitoring
Report Summary
2002

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, Burton Road, 164th Avenue, 134th Street, Mill Plain-East, SR-503-South, and SR-502. Planned improvements along Burton Road are likely to reduce the congestion index in this corridor.

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Speed as Percent of Speed Limit

RTC has contracted with Clark County to collect travel time data along congestion management corridors. This is in addition to the travel time data that the County is already collecting for concurrency purposes. The methodology for collecting the travel time data was consistent along all corridors. 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 freeway facilities are close to the posted speed limit. Facilities that operated at 65% or lower of the posted speed include Mill Plain-East, SR-500, Fourth Plain Boulevard, Burton Road, Main Street, 164th Avenue-South, and Andresen Road.

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Auto Vehicle Occupancy

Automobile occupancy is calculated by counting passenger vehicles at a given location and the number of people in each vehicle. The number of people divided by the number of passenger vehicles is the automobile occupancy for that location. Automobile occupancy information has been collected at twenty locations throughout Clark County.

In general, freeway facilities display lower automobile occupancy than arterial facilities. This difference is likely due to a greater number of work trips on freeways, where drive alone trips are more 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 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. SR-14, I-5 and I-205 corridors have truck percentages above 5%. Fourth Plain and Mill Plain Boulevards (SR-501) from I-5 to the Port of Vancouver both have percentages greater than 10%. I-5 North and I-205 Central also have truck percentages above 10%.

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This report was prepared by: