A draft traffic report on the intersection of Washington Street and Ash Coulee Drive is lending little support for the need for a signal light.

The Advanced Traffic Analysis Center provided the draft report and its findings at the Bismarck City Commission meeting on Tuesday. Earlier this year, the commission asked for the report in response to a Horizon Middle School parents' group's concern over the safety of the intersection and traffic congestion associated with dropping off and picking up of students.

In light of the report, which was accepted by the commission, it was decided to take no action yet and study the situation again after the completion of two network roads, which are expected to relieve traffic congestion by 30 percent. Valley Drive and a connection to Medora Avenue are expected to provide alternate routes to Horizon Middle School and be complete by as early as this fall.

"What I got from the report is that we should take a cautious approach before we put in a stop light or make road improvements without warrants," Mayor John Warford said. "It is a good study and shed a strong light on the subject. We'll definitely keep it on the radar screen. After hearing everything, I think that taking no action and waiting to study it later is prudent."

ATAC's Jason Baker and Shawn Birst presented the information to commissioners. ATAC collected 16 hours of traffic data on the intersection, from 6 a.m. to 10 p.m. Feb. 7. The data was used to develop a delay study for the morning and afternoon peak periods; traffic signal warrants; delay time comparisons between a two-way stop, four-way stop and signalized control; traffic signal analysis using future road network and land development; and recommendations.

Traffic count peaks occur at the same time each day, 7:15 to 8:15 a.m. and 3:15 to 4:15 p.m., coinciding with the dropping off and picking up of students at Horizon.

The average delay at the eastbound approach of Ash Coulee during the morning peak was 13.9 seconds with a maximum delay of 50 seconds. During the afternoon peak, the average wait was 22.7 seconds, with a maximum of 73 seconds.

On the westbound approach of Ash Coulee, during the peak morning period, the average delay was 27.2 seconds, the longest delay being 199 seconds. The afternoon peak saw an average wait of 13.7 seconds and a maximum wait of 64 seconds.

Baker told commissioners that the greatest influx of vehicles at the intersection roughly occurred during a 10-minute period twice a day during the peak hours.

There are eight factors (warrants) that determine the necessity for placement of a traffic signal at an intersection. Presently the Washington-Ash Coulee Drive doesn't meet any of them.

Three of the warrants involve vehicle volume, two involve pedestrian use and the others are coordinated signal system, crash experience and roadway network.

Based on traffic volume and future projections, the earliest the intersection will qualify for federal funding for a signal will be 2015.

"Pedestrian warrants weren't met because there weren't any seen," Baker said. "To meet crash experience warrants, you have to have five within a 12-month period. The city's crash data shows there have been a total of seven since 2002, and only five were applicable to the intersection."

"It is the popular misconception that the installation of a traffic signal will always optimize the operation of any intersection," the report says.

"The most common arguments for the placement of a traffic signal are safety and delay. Traffic signals can reduce the number of broadside and left-turn accidents, but in many cases the number of rear-end accidents increase. In addition, an unwarranted signal may actually increase the overall delay incurred at an intersection."

The average delay at the two-way stop is 6.6 seconds, Baker said. Using specially developed software, it was determined that a four-way stop would increase the delay to 8.4 seconds, while a traffic signal would increase the delay to 7.8 seconds.

In studying the developing roadway network, ATAC figures that the addition of Valley Drive, to be constructed this summer, and a private connection by Horizon to Medora north of the school will reduce congestion at the intersection by 30 percent. City traffic engineer Mark Berg said most of this reduction will be attributable to Valley Drive, which provides a more direct route for commuters living in northwest Bismarck.

Short-term ATAC report recommendations are:

3 Do nothing; traffic congestion at the peak hours will be alleviated by construction of new roadways.

3 Educate drivers and parents in an effort to manage expectations regarding delays times. "Perhaps just planning to arrive 10 minutes earlier could greatly help matters," Baker said.

3 Monitor the intersection operation in the fall to determine any changes in traffic patterns.

3 Extend the eastbound right-turn lane to increase the capacity.

Baker said that the eastbound right turn lane could hold only four cars, and when this fills, the overflow backs into the regular lane of traffic.

There was little discussion on the report's analysis by the commission following the presentation. A motion was approved to accept the report.

"This brings a lot of clarity to the the issue," Warford said. "We'll see 30 percent improvement with the new roads and we're dealing with a 10-minute peak at both ends, going and leaving. I would think that drivers in that area can be innovative and mitigate the traffic problems fairly easily."

(Reach reporter Gordon Weixel at 250-8255 or gordon.weixel@;bismarcktribune.com.)