Counting up the cars at school

Late last month, the School Board heard again from Transpo, the traffic consultant evaluating how traffic patterns and volumes around the high school and throughout the nearby community, will change after an expanded and remodeled high school begins receiving students in 2017.

Transpo was charged with estimating the impact on local streets and intersections that would result from the construction of a 15,000 sq. ft. expansion and 10-classroom addition to Mercer Island High School in three years time. The remodeled and enlarged school would accommodate 1525 students. Much of the expansion would take place along the southeastern corner of the existing school land. Yet the impact on traffic will be spread over all directions.

The plans include changing the configuration and location of drop-off points, bus zones and parking. It does not include the additional traffic impacts from a proposed fourth elementary school planned for the present location of Youth Theatre Northwest and adjacent buildings, on S.E. 40th Street.

Transpo used historical data from 2005 and updated traffic data from more recent studies done in 2012. The consultant’s report estimates that the expanded high school campus will generate 250 more trips each day.  Of that amount, 80 more trips would occur during the morning peak than what occurs on a school day now.

The consultant also looked at 12 key intersections affected by the school. They include five intersections along S.E. 40th Street beginning at Island Crest Way and S.E. 40th Street and ending at 92nd Avenue S.E. Next, two key points along S.E. 42nd Street, the northern border of the school block at 86th Avenue S.E. and 92nd Ave S.E., are also included. Heading south along Island Crest Way, four more intersection are part of the study; S.E. 44th Street, 86th Avenue S.E. and two intersections at S.E. 47th Street. Also on the list and furthest away from the site, is an intersection at North Mercer Way and S.E. 36th Street.

Data from the city of Mercer Island and the consultant traffic studies indicate that some of the key intersections are already classified as below the city’s accepted level of service. Level of service at an intersection is measured by the average delay per vehicle that uses the intersection. The Transpo report says that if no improvements are made to those intersections before the expanded high school is finished, most will fall further below standard. However, plans for drop off points, parking and traffic flow changes, are designed to help with congestion.

School officials will look for help from the city in mitigating traffic impacts at the affected intersections.

“It is my hope that the city will work with the district to improve these intersections for all that would be affected,” said Superintendent Gary Plano.

The traffic consultant also looked at safety at each of the intersections and for four key roadway segments. Using data for 2010, 2011 and 2012, the number of collisions at the 12 intersections totaled 38, with the highest number occurring at S.E. 40th Street and Island Crest Way. The three year average accident rate is 5.3 per year. The intersection with the next highest accident rate is 47th Ave S.E. and Island Crest Way, where a total of seven accidents occurred over the last three years for an average of 2.3 incidents per year. There is one fatality recorded during the three year period that occurred on Island Crest Way.

Given industry standards study intersections were not designated as dangerous.

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