Parking and Traffic Analysis Seattle, WA Prepared for: URS Corporation 1501 4th Avenue, Suite 1400 Seattle, WA 98101-1616 Prepared by: Mirai Transportation Planning & Engineering 11410 NE 122nd Way, Suite 320 Kirkland, WA 98034
Table of Contents Executive Summary... 1 Introduction... 3 Existing Conditions... 3 Traffic Conditions... 3 Level of Service Traffic Operations... 4 Level of Service Traffic Operations... 5 Existing Level of Service... 5 Parking Supply... 6 Parking Demand Summer Conditions... 8 Parking Demand School Conditions... 10 Future Conditions: Impact of the Proposed Project... 12 Analysis Assumptions... 13 Analysis Assumptions... 14 Future Traffic Conditions... 14 Future Level of Service... 16 Parking Demand Future Conditions... 16 Potential Mitigation... 17 List of Tables Table 1. Summary of Proposed Parking Supply...1 Table 2. Summary of Parking Demand...2 Table 3. Summary of Peak Hour and Daily Traffic Conditions...2 Table 4. Level of Service Definitions...5 Table 5. Existing (2007) LOS Results (School Year)...6 Table 6. Summary of Changes to Parking Areas...12 Table 7. Estimate of Future Peak Hour Trips Generated for 1,400 Students...14 Table 8. Intersection Level of Service with Proposed Project...16 Table 9. Estimate of Future Parking Demand and Supply at 1,400 Students...17 Page i
List of Figures Figure 1. Existing Traffic Volumes...4 Figure 2. Parking Supply at and Vicinity...7 Figure 3. Summer Parking Utilization...9 Figure 4. School Year Parking Utilization...11 Page ii
EXECUTIVE SUMMARY Mirai Transportation Planning and Engineering reviewed the parking and traffic impacts associated with the planned increase of the student population from 1,125 to 1,400 Nathan Hale High School. The following highlights the major findings of the study. Parking Supply The proposed project site plan would change the number of parking spaces within the school s main parking areas. Table 1 summarizes the proposed parking supply. The proposed project would provide 292 parking spaces on-campus, a net increase of 8 spaces. Currently there are approximately 284 parking spaces. In some parking areas, such as near the athletic fields, parking is poorly defined and was estimated. The proposed project would better define parking areas and provide additional parking to accommodate the increased student population. Table 1. Summary of Proposed Parking Supply Existing Proposed Change Main Parking Area 136 136 0 Northwest Parking Area 74 83 9 Athletic Fields Parking Area 58 62 4 Maintenance Parking Area 16 11-5 Total School Parking 284 292 8 Parking Demand is planning for a future increase from 1,125 to 1,400 students. The following summarizes the impact of the additional students on parking demand. Table 2 summarizes the parking demand for a typical school day. With the increase in students from 1,125 to 1,400 the typical school parking demand would increase by 77 spaces to 289 spaces. Compared to the proposed supply, there would be a 3 space surplus. Page 1
Table 2. Summary of Parking Demand Existing (1125 Students) Proposed (1400 Students) Change School Day Parking Demand 212 289 77 School Day Capacity 284 292 8 School Day Surplus/Deficit 72 3-69 Peak Hour Traffic Nathan High School s student population increase from 1,125 to 1,400 students in the future will increase the number of vehicles entering and exiting the school site during peak times. The following summarizes the impact of the additional students on the school driveways and intersections during the school s afternoon peak hour. Table 3 summarizes the total, entering and exiting trips during the peak hour of a typical school day (2:45 PM to 3:45 PM). Estimated daily trips are also reported. The total new trips generated by the increase in student population would be 77 during the PM peak hour and 470 daily. Traffic at adjacent study intersections, other than the student driveway, would continue to operate at acceptable conditions (LOS B or better) during the school s peak hour with the 1,400 student population. Under existing conditions, the main student access on 30th Avenue NE (west student driveway) currently operates at LOS E during the afternoon peak hour. Based on observations and traffic count data, this condition exists for 15 to 20 minutes. With the student population increase, the main student access on 30th Avenue NE, would operate at LOS F during the afternoon peak hour. It is expected that this condition would occur primarily during a 15 to 20 minute period following the school s dismissal. Creation of a left turn lane for vehicles exiting the main student access would improve the intersection s operation from LOS F to LOS D during the peak hour. Table 3. Summary of Peak Hour and Daily Traffic Conditions Existing (1125 Students) Proposed (1400 Students) Change Peak Hour Trips 314 391 77 Entering Trips 56 81 25 Exiting Trips 258 310 52 Daily Trips 1,924 2,394 470 Page 2
Parking and Traffic Impact Analysis INTRODUCTION Mirai Transportation Planning and Engineering reviewed the parking and traffic impacts associated with the modernization of the and the planned increase of the student population from 1,125 to 1,400. Mirai reviewed existing conditions and estimated the future impacts with proposed improvements. This project provides a supplement of previous analysis completed for the Building Excellence (BEX) II Draft and Final EIS. EXISTING CONDITIONS Mirai documented the existing traffic and parking conditions to understand the high school s impact on the surrounding street system and neighborhoods. Traffic counts were conducted at area intersections and school driveways during the school year. Parking data were collected prior to and after the beginning of the school year to identify differences in area parking demand. Traffic Conditions Traffic counts were collected by TC2.com, on Tuesday, September 18, 2007. This was a latestart day, with the final period ending at 3 pm. All traffic counts were conducted between 2 and 4 pm to capture the peak period of school activity. Traffic counts were collected at three locations: NE 110th Street/30th Avenue NE Northwest Driveway/30th Avenue NE NE 107th Street/30th Avenue NE (Driveway access) Of the driveways measured, nearly 320 trips were recorded either entering or exiting the site during the peak hour. The primary movement out of the driveways is to the south on 30th Avenue NE with about two-thirds of the exiting volumes (174 out of 258 trips). The south leg of NE 110th Street/30th Avenue NE is a major pedestrian corridor with more than 70 pedestrians crossing during a one-hour period. Figure 1 shows the traffic and pedestrian volumes during the school s afternoon peak hour. Page 3
Figure 1. Existing Traffic Volumes Page 4
Level of Service Traffic Operations Level of Service (LOS) is a measure of the quality of traffic operations at an intersection. LOS is described using an A to F scale, with LOS A representing minimal traffic delays and LOS F representing severe congestion and long delays. The LOS is determined by measuring the average control delay per vehicle. For all-way stops, an overall intersection LOS and delay is reported. For intersections with stop controls only on the minor streets, the LOS and delay reported reflects the worst individual movement of the study intersection. Table 4 describes the LOS for unsignalized intersections. Table 4. Level of Service Definitions LOS Description Unsignalized Delay per Vehicle (sec/veh) A Few or no delays 0-10 B Short traffic delays >10-15 C Average traffic delays >15-25 D Long traffic delays >25-35 E Very long traffic delays >35-50 F Extreme traffic delays with intersection capacity exceeded >50 Source: Highway Capacity Manual (HCM 2000, Transportation Research Board) Existing Level of Service The LOS calculations reflect the worst or peak volumes during the school day, approximately 15 minutes after school is dismissed for the day. The collected traffic data were entered into a Synchro (Version 6, Build 614) intersection analysis program to calculate the existing delay and LOS. The Synchro program uses a variety of traffic data to calculate the operation of an intersection, including: traffic counts, lane configurations, pedestrian volumes and type of intersection controls. The end of the school day is clearly reflected in the results, particularly on the operating of the west driveway. The rush of students leaving the school lowers the driveway s operation to LOS E with a more than 300 feet of cars lined up to exit. The traffic counts indicate that this condition is short-lived and within 15 minutes, the exiting volume of the west driveway has dropped from 171 vehicles to 10 vehicles. Table 5 shows the results of the LOS analysis. The Synchro LOS analysis reports are found in the Appendix to this document. Page 5
Table 5. Existing (2007) LOS Results (School Year) Level of Service/Average Delay School Peak Hour Intersection (2:45 to 3:45 PM) NE 110th Street/30th Avenue NE A / 9.7 Northwest Driveway/30th Avenue NE B / 10.5 NE 107th Street/30th Avenue NE (West Driveway access) E / 12.3 Parking Supply Mirai conducted a count of parking spaces within the school campus and within the walking distance of campus along neighboring streets. Figure 2 identifies the number of legal parking spaces and parking controls along each block face. On-Campus Mirai conducted a count of available parking spaces within the school campus. There are four parking areas. The northwest and main parking areas are striped and are open to students and faculty. In contrast, the athletic fields parking area is largely undefined, with only a few areas of striped parking. A sign at the entrance indicates that parking is for only permitted vehicles. Within this area, there are areas that could be used for parking, but have been fenced off. In addition, there are offset T-shaped landscaped parking features which only provide a limited number of spaces. Other undefined parking areas occur along the outdoor basketball court, particularly along the southern fence. Based on our observation, we determined the total parking supply on-campus to be 284 parking spaces in four primary areas: Main parking lot This is the main parking area for students with 136 parking spaces, including eight handicapped spaces. Approximately 7 additional spaces are currently striped out in front of pathways to surrounding uses. Northwest parking lot This parking area has 74 spaces, including five handicapped spaces. Athletic fields parking area This parking area provides 58 spaces. Maintenance area There are approximately 16 spaces between the Main and the Northwest parking lots used for maintenance activities. Page 6
Figure 2. Parking Supply at and Vicinity Page 7
Neighboring Streets Mirai completed a parking supply analysis of streets within approximately 0.2 miles of the school entrance. The study area is bounded by NE 113th Street to the north, 35th Avenue NE to the east, NE 105th Street to the south and Lake City Way NE to the west. The intent of the parking supply analysis is to determine the number of spaces available and provide a base to determine parking occupancy rates. The parking supply follows the City of Seattle methodology used by the Department of Planning and Development (Client Assistance Memo #117). The analysis measures the length of the street edge available for parking; deducts from the measurement distances required from features such as driveways, intersections and fire hydrants; and then determines the number of legal parking spaces based on the remaining street lengths. In the adjacent neighborhoods, parking is largely undefined. As a result, in some areas, vehicles may park completely off the edge of the paved road, while in other areas vehicles may park partially on the paved roadway. Parking control signs are sporadic and seem to respond to streets where issues have arisen. In other locations, there are private parking areas where the parking or driveways for private buildings eliminate the possibility of parking along the roadway s edge. Parking Demand Summer Conditions Parking demand is the number of spaces needed to serve a particular use. One measure that relates the parking demand to the supply is Parking Utilization. Parking utlization indicates how full parking is along a particular street or within a parking lot. The measure is calculated by dividing the number of occupied spaces by the parking supply. Parking demand can exceed the legal parking supply and parking utilization rates may exceed 100 percent in areas where parking is in high demand. Generally, parking utilization levels above 80 percent for on-street and above 95 percent for parking lots are considered fully-occupied. Mirai counted the number of parked vehicles during the early afternoon (1 to 2 pm) during the last week of August to indicate a baseline of parking demand during summer conditions when school is not in session. Figure 3 shows the parking utilization during summer conditions. On-Campus On-campus parking lots were not counted during the summer, but were assumed to be lightly used. Page 8
Figure 3. Summer Parking Utilization Page 9
Neighboring Streets Parking throughout the neighborhood areas surrounding the school was generally light during the summer. Parking on the streets immediately adjacent to the school varies between 0 and 40 percent. Streets where the parking utilization was 50 percent or more includes: The west side of 31st Avenue NE between NE 110th St and NE 113th Street The east side of 34th Avenue NE between NE 110th St and NE 113th Street Both sides of NE 110th Street east of 35th Avenue NE The south side of NE 113th Street west of 27th Avenue NE The west side of 28th Avenue NE, north of NE 107th Street Parking Demand School Conditions A second parking demand count was conducted following the third week of school during the early afternoon (1 to 2 pm). This count identified the parking demand during the school year within the campus parking lots and on neighboring streets. The on-campus lots were counted during subsequent field visits to confirm the results. Figure 4 identifies the parking utilization during the school year. On-Campus Overall, parking in the school lots is approximately 75 percent of capacity during the school year. Observed parking on the campus varied between 52 and 92 percent of the parking supply. In the main parking area, approximately 100 of the 136 spaces were occupied during the peak demand period (74 percent utilized). Traffic counts at the driveway found 168 exiting trips during the peak 15 minute period, implying that pick-up activity is also occurring within the lot. The northwest parking area was 92 percent utilized with 68 out of the 74 spaces occupied. The athletic fields parking area was about 52 percent utilized, with 30 out of 58 spaces occupied. Page 10
Figure 4. School Year Parking Utilization Page 11
Neighboring Streets Parking demand during a typical school day seems to be largely handled on campus and has only a minimal impact on adjacent neighborhood areas. Compared with the summer parking conditions, our analysis of school conditions found: An increase from 0 to 20 percent utilization on NE 107th Street west of 30th Avenue NE. A 12 to 32 percent parking utilization on streets surrounding the High School campus similar to the summer conditions. A 75 percent parking utilization within the High School s parking lots. The results indicate that the campus parking lots accommodate the school s parking demand during the typical day with little impact to adjacent neighborhood streets. FUTURE CONDITIONS: IMPACT OF THE PROPOSED PROJECT The improvements at will provide for an increase in the student population from 1,125 to 1,400 students. Figure 5 shows the proposed site plan that responds to the expected increase in traffic and parking, while improving the on-campus facilities. The proposed project, part of the District s Building Excellence program, would add new facilities and replace older facilities including the library. Table 6 summarizes proposed changes to the parking areas. Main parking lot This parking area would be unchanged retaining 136 spaces. Northwest parking lot This parking area would be increased to 83 spaces, a 9 space increase. Athletic fields parking area This parking area would be better defined and re-striped to provide 62 spaces. Maintenance area There would be approximately 11 spaces between the Main and the Northwest parking lots used for maintenance activities. Overall, the project would provide 292 on-site parking spaces. Table 6. Summary of Changes to Parking Areas Existing Proposed Change Main Parking Lot Northwest Parking Lot Athletic Fields Parking Lot Maintenance Area Total Parking 136 136 0 74 83 9 58 62 4 16 11-5 284 292 8 Page 12
Figure 5. Proposed Site Plan for Page 13
Analysis Assumptions Mirai investigated how these changes in parking would meet the anticipated student and staff demand and would affect the traffic operations at the study intersections. To estimate future traffic and parking demand, the study included the following assumptions: The existing (1,125 students) population would retain the current demand profile for parking facilities and for automobile trips. We do not anticipate a change in the commuting habits of this population. The existing trip rate is 0.28 trips per student during the afternoon peak hour, identical to the reported rate for high schools in the Institute for Transportation Engineers (ITE) Trip Generation Manual (2003). The trips associated with the 275 additional students are assumed at the ITE Trip Generation rates. This will provide a conservative estimate of the future travel demand at the school. Daily trips are based on the ITE Trip Generation Manual. A 1.0 percent growth rate on area roadways to reflect traffic increases. Review of City traffic data indicates that recent annual traffic growth in the area is approximately 0.7 percent annually. Growth rates were applied to non-school related traffic volumes for two years to reflect the near-term future traffic conditions. No roadway or intersection improvements are assumed. Future Traffic Conditions Future traffic conditions assume that area traffic growth increases at an average of 1 percent per year and 275 new students will be added to the population of. Table 7 shows the estimated peak hour and daily trips for the future student population. Table 7. Estimate of Future Peak Hour Trips Generated for 1,400 Students Entering Trips Exiting Trips Students Trip Rate Total Trips Peak Hour Existing Conditions 1125 0.28 314 56 258 Additional Students 275 0.28 77 25 52 Future Conditions 1400 0.28 391 81 310 Daily Existing Conditions 1125 1.71 1,924 962 962 Additional Students 275 1.71 470 235 235 Future Conditions 1400 1.71 2,394 1,197 1,197 The additional student trips were assigned to the study intersections based on the location of future parking and current trip patterns. Figure 6 shows the future traffic volumes. The future volumes were calculated by multiplying the 1 percent growth factor to the existing traffic volumes for two years (non-school related) and then adding the new trips generated by the additional student population. Page 14
Figure 6. Future Peak Hour Traffic with 1400 Students Page 15
Future Level of Service The future traffic operations at the study intersections are acceptable, except for the main school driveway at NE 107th Street/30th Avenue NE. Based on the analysis, the West Driveway would operate at LOS F during the school s peak hour. As is the circumstance today, this poor operating condition would be related to left-turning vehicles exiting the site immediately after the day s dismissal and would be limited to only 15 to 20 minutes. Vehicle queue could extend to 400 feet (approximately 20 vehicles). Most of the impacts from the LOS F would be contained on-site, with the delays and vehicle queues primarily being experienced by vehicles exiting the site. Table 8 compares the existing and future conditions with the projected LOS for each of the study intersections. The future distribution of traffic to the site would change to reflect the location and size of the parking facilities. Table 8. Intersection Level of Service with Proposed Project Intersection Existing Level of Service/Average Delay (1125 students) Future Level of Service/Average Delay (1400 students) NE 110th Street/30th Avenue NE A / 9.7 B / 10.2 Northwest Driveway/30th Avenue NE B / 10.5 B / 10.7 NE 107th Street/30th Avenue NE (West Driveway access) E / 49.6 F / 60.3 Field Driveway/30th Avenue NE B / 10.5 B / 10.0 Parking Demand Future Conditions The estimate of future parking demand followed the methodology used in the traffic analysis. Mirai estimated the future parking demand based on the increase in the student population at. The parking demand for the existing student population was assumed to be captured in the field results (212 spaces). The parking demand for the additional 275 students was estimated using the ITE Parking Generation (3rd Edition) average demand rates for suburban schools. The analysis showed that 77 additional parking spaces would be required to meet the future peak parking demand. For the future population of 1,400 students, a total of 289 spaces (212+77) would be needed to meet the peak parking demand. Table 9 summarizes the peak parking demand calculation for the proposed student population. Page 16
Table 9. Estimate of Future Parking Demand and Supply at 1,400 Students Students Peak Demand Rate Peak Parking Demand Existing Peak Demand 1125 0.188 212 Additional Student/Staff Demand 275 0.280 77 Total Future Demand 1400 289 The proposed project would provide 293 on-site spaces, exceeding the predicted demand by four spaces. If students and staff are allowed to use any available parking there would be more than adequate parking supply to meet the typical parking demand associated with the site. POTENTIAL MITIGATION Most of the project impacts will be contained within the Nathan Hale site. Only the intersection of NE 107th Street/30th Avenue NE (West Driveway access) will operate at a poor level of service (LOS F) during the afternoon peak period. This impact corresponds with the school s dismissal and is of only 15 to 20 minutes in duration. Page 17