COM 0649.004 2002-2004 - Laserfiche WebLink

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The MUTCD lists four primary criteria based on traffic volumes and accident experience to determine whether or not a four way stop is warranted. It also lists four optional criteria based on engineering judgment. A ten hour manual traffic count was taken at the intersection on September 9, 2003, to provide traffic volume data to measure against the warrants. The County provided traffic accident data to measure against the traffic accident experience warrant. A field inspection determined that only one of the four optional warrants pertaining to controlling left turn conflicts could be evaluated. "Before and after" spot speed studies were conducted to determine if any changes in traffic speed on Nani Kailua Drive occurred as a result of the four way stop. The counts were taken on June 26, 2003, about a month before installation, and on August 28, 2003, about a month after installation. The members of the Kona traffic Safety Committee were contacted by email for their opinions at the start and near the completion of the study. Results of the Evaluation. The results for the three sets of criteria are discussed in the following paragraphs. With respect to the warrants listed in the MUTCD, none of the two primary traffic volume -related and traffic accident -related warrants are met. There are not enough vehicles at the intersection to warrant either traffic signals or a four way stop. There are also not sufficient numbers of vehicles to cause left turn conflicts; therefore, the one optional criterion is not met. With respect to speed changes effected by the four way stop, the following table summarizes the "before and after" results: Number of samples Average speed (mph) Minimum speed (mph) Maximum speed (mph) <20 mph 20-30 mph 31-35 mph >35 mph DOWNHILL RESULTS BEFORE AFTER 229 185 32.6 28.8 9 16 55 57 4(2%) 5(3%) 89(39%) 116(63%) 72(31%) 44(24%) 64(28%) 20(11%) UPHILL RESULTS BEFORE AFTER 256 222 30.8 26.0 17 13 44 52 4 (2%) 12(5%) 125(49%) 184(83%) 80(31%) 20(9%) 47(18%) 6(3%) There were 3.8 mile per hour (mph) and 4.8 mph decreases in average speed on the downhill and uphill directions of travel, respectively. Both of these differences are statistically significant at the 90% confidence level. The proportion of vehicles in the "20-30 mph" category also increased significantly, while the percentage in the "greater than 35" mph category decreased significantly, also. These changes indicate that the four way stop has had a