Editor’s note: For many years until he retired, former Methow Valley News columnist Bob Spiwak diligently documented traffic on Highway 20 (near West Boesel) on the Memorial Day and Labor Day weekends, and extrapolated conclusions from the data. Mazama resident Gerald Smith voluntarily resumed the traffic count over the recent Memorial Day weekend. “Methow Valley News readers have missed Bob Spiwak’s good-humored tradition of tabulating traffic on Memorial and Labor Day holidays,” Smith said in an email. “In that spirit, but lacking the Spiwak wittiness, the following technical report might be of general interest to residents of the Methow Valley who have a love/hate relationship to Highway 20’s summer flood.”
First, a brief summary of the Spiwak methodology and a meta-analysis of his results from the five years of data available electronically. According to a Spiwak history of the traffic count (see his column dated Sept. 10, 2015), a single hour of data has consistently been recorded at a non-peak hour which has typically been 9-10 a.m. but for some years has varied slightly from these exact hours. Initial recordings were made on paper with hash marks designating westbound and eastbound vehicles. Later counts made use of hand-operated digital meters with a thumb actuated trigger. Using each methodology, relatively low error rates are likely attainable –probably less than 1% error on any given count.
For any given year, traffic flow patterns are likely affected by weather on the measurement day as well as the previous week due to population influx effects before the holiday and timing of the return trip (early or later in the day). Thus, when looking back at the Spiwak data, Memorial Day traffic varied considerably year-to-year (range: 348 to 484 vehicles westbound and 63 to 91 eastbound). Expressed as mean plus-or-minus standard deviation, the Spiwak results suggest that a typical Memorial Day traffic rate is 355 plus-or-minus 44 vehicles westbound and 78 plus-or-minus 13 eastbound. [Note that in his statistical reporting, “vehicles” typically did not include motorcycles, which were reported separately. For purposes of the meta-analysis, Spiwak motorcycle counts were included in the vehicle count calculated and reported above.] Combining west and eastbound counts, total traffic passing the Spiwak recording site (at West Boesel between Winthrop and Mazama) was typically 433 plus-or-minus 55 vehicles with 82 plus-or-minus 1% of the traffic being westbound.
The most-recent Spiwak data found recorded in the Methow Valley News electronic archives was for 2016. Meta-analysis results reported above were for years 2012 to 2016. Thus an update to this important database with more current data would be a useful addition to the literature. A slightly modified methodology was originated with this 2019 data collection. To help elucidate potential destinations, the count was sited at the intersection of Highway 20 and the Lost River road (approximately 0.4 kilometer from the Mazama store, Goat’s Beard Mountain Supplies and the Corral Trailhead). Vehicle counts for through traffic continuing west or eastbound on Highway 20 were made and in addition, counts of vehicles turning on to Lost River road or on to Highway 20 from Lost River road were recorded along with their west or east direction. Vehicles were further differentiated by car, pickup truck, motorhome, motorcycle and bicycle. Data were collected starting at exactly 9 a.m. and stopping at 10 a.m. on Monday, May 27, 2019. Manual hash tag methods were used to record each vehicle direction and type. Similar to the Spiwak data collections, error rates in recording were likely less than 1%.
Memorial Day weather in the morning was sunny with temperature increasing from 62° to 67° F from 9 to 10 a.m. as measured by the Northwest Avalanche Center station located about 1K from the traffic counting site. Traffic flow was observed to typically pass in waves of vehicles with relatively large gaps between each wave. Total vehicles through the intersection was 356 (299 westbound and 57 eastbound; 84 and 16% respectively). While most vehicles were traveling through the intersection on Highway 20, an important fraction of the traffic turned onto Lost River road toward Mazama (66 vehicles or 19%). A somewhat larger fraction (87 vehicles or 24%) turned onto Highway 20 from Lost River road.
Spiwak speculated about but did not record the proportions of vehicle types flowing through the Methow valley. In the current study, vehicle types were recorded. Cars (including SUVs) accounted for 57% of the traffic, pickup trucks were 37%, motorhomes were 3%, motorcycles (four) were only 1% and bicycles (three) were less than 1% of total vehicles. It was also noted that 27% of the pickup trucks were pulling large trailers for mobile accommodation. Others were pulling boats but these were not enumerated.
Comparison of the Spiwak total vehicles (433 plus-or-minus 55) with the 2019 count of 356 suggests that somewhat lower-than-normal travel was undertaken during the Memorial Day morning. The total was similar to the lowest number Spiwak recorded (348 vehicles in 2014). This might be due to the very pleasant weather which followed several damp days and perhaps postponed travel departure times for visitors to the valley in 2019. Alternatively, the recording site at the Mazama intersection on Highway 20 was up valley from the Spiwak site by about 12K and could have influenced traffic density in unexpected ways.
In summary, Highway 20 traffic through Mazama on Memorial Day morning was largely (more than 80%) heading westbound toward Washington Pass. This is in good agreement with earlier studies by Spiwak.