Problems and Causes
The southbound Raye Street exit has a tight turning radius that causes vehicles to slow in the outside through lane approaching the intersection. In addition to this constraint, the intersection of Queen Anne Drive/4th Avenue/Raye Street has vehicle queues that back up onto SR 99 North. During the p.m. peak period, these queued vehicles can take as long as 4.5 minutes to travel from the Aurora Bridge through this intersection. In this area, the intersection of Queen Anne Drive/4th Avenue/Raye Street currently operates at LOS F in both the a.m. and p.m. peak hours.
The queued vehicles create a potential for rear-end accidents. The narrow lanes on the Aurora Bridge also create the potential for sideswipe accidents involving these queued vehicles.
The traffic entering SR 99 N. southbound from Raye Street is also problematic. There is no acceleration lane for these vehicles, so they must directly enter the traffic flow from a stop. Coupled with the high volumes and speeds on SR 99 N., this creates the potential for rear-end and entering-at-angle accidents.
As noted in Chapter 3, a total of 94 accidents occurred in the 0.65 mile section of SR 99 between the Halladay and Raye Street intersections and the north end of the Aurora Bridge.
Options Considered
Several options were considered to address the traffic congestion and safety issues in this area including: adding a southbound off-ramp, converting the outside lane to a drop and add lane, improving signing, installing a new traffic signal, and rerouting traffic.
Similar to the Halladay Street proposal, converting the existing outside lane to a drop lane was eliminated because of the resulting queuing and accidents that would likely occur on SR 99 North.
Signing improvements were considered as a stand-alone recommendation, but would likely have little impact on the traffic operations or accident experience in this area. The size and location of signs on the Aurora Bridge is restricted; as signs can only be mounted on luminary poles and have to be small enough not to overload the poles during windy conditions. These limitations also reduce the effectiveness of this option.
Recommendations
The recommendation for the Raye Street intersection is a staged approach incorporating multiple options listed above. The main benefit of the staged approach is that it minimizes impacts to nearby residents for as long as possible, until further improvements are needed. There is no timetable set for implementing each stage, as a reevaluation of the area would be needed after every improvement to determine its effects. The stages presented could be modified in the future to address changes in traffic patterns or the effects previous improvements have on accidents and traffic congestion in the area. The four stages of the Raye Street recommendation are:
Stage 1 of the recommendation would be to improve the Queen Anne Drive/4th Avenue/Raye Street intersection. This intersection was identified as the contributing cause for much of the traffic congestion in the area and therefore would be the first hot spot to be improved. The recommendation is to add a traffic signal and reduce the number of approaches at the intersection. By closing some of the approaches to this seven-leg intersection, a traffic signal could be installed and improvements to traffic flow and queue reduction could be realized. The closed streets could still access this intersection through other routes. The City of Seattle has jurisdiction over this location and has agreed to take a detailed look at ways to implement these changes.
Stage 2 of the recommendation would include the Halladay Street recommendation, and would add a signal at the Halladay Street/6th Avenue intersection. The operation of this signal will be determined by the City of Seattle, but it will need to balance the 6th Avenue traffic volumes with the northbound SR 99 N. existing volumes.
Stage 3 would reconstruct the Raye Street intersection with SR 99 N. as well as add an acceleration/deceleration lane between the Raye Street on-ramp and the Dexter Way off-ramp. A new ramp bridge would be constructed to allow vehicles to exit southbound SR 99 N. at a greater speed, reducing the risk of rear-end accidents and improving traffic flow of SR 99 North. Work along Dexter Avenue North would include signalization of two intersections (with Dexter Way North and with 6th Avenue North) and some rechannelization between the intersections. The existing bicycle lane along Dexter Way would remain as it is today. Sixth Avenue N. would also be reconstructed between the Stage 2 work and the intersection with Dexter Avenue to improve the intersection alignment and to allow larger vehicles to use the intersection.
Stage 4 of the recommendation would only be constructed as a last resort if the previous stages did not significantly improve traffic flow and reduce accidents within the Queen Anne area. This stage would remove the Raye Street off-ramp bridge constructed in Stage 3 (making Raye Street a one-way street onto SR 99 N. southbound) and rerouting westbound Queen Anne traffic to the Dexter Way N. off-ramp. Queen Anne traffic would then travel on Dexter Avenue, 6th Avenue, and Queen Anne Drive to get to the Queen Anne Drive/4th Avenue/Raye Street intersection. Stage 4 would also modify the 5-legged intersection and signal built in Stage 1 to accommodate a one-way eastbound Raye Street.
The traffic signal timing at the intersection of Halladay Street and Queen Anne Drive will need to be revised with the change in traffic patterns caused by the rerouting. The timing of this signal will be determined by the City of Seattle, but will need to balance the rerouted traffic volumes with the northbound SR 99 N. exiting volumes. The projected 2030 a.m. and p.m. peak LOS for this location are B and D respectively.
This new route is estimated to take 4.5 minutes to travel during the p.m. peak period and will continue to operate at this level up to year 2015. The 2030 LOS at the Queen Anne Drive/4th Avenue/Raye Street intersection will be F in both the a.m. and p.m. peak hours. This intersection will, however, have significantly less queuing than the no-action option.
Without the improvement, the p.m. peak traffic projections show traffic would be queued across the entire length of the Aurora Bridge.
The details associated with all stages of this modification will need to be refined as they go forward as actual improvements. Specifics regarding signal operations, specific roadway geometrics, and pedestrian and bicycle facilities will be determined at that time.
The estimated cost to construct all the improvements associated with Queen Anne access is $19.8 million. The largest cost is the construction of the new ramp at Raye Street. The cost estimate is in 2002 dollars and estimated at mid-point of construction (year 2017). No specific timeframe has been determined, but this year was used to be consistent with the cost estimates in other areas of the corridor.
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