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I-5 Express Lane Operation on Weekends

February 6, 2018

Express lanes concept

The Washington State Department of Transportation uses express lanes on I-5 to improve traffic flow during peak travel times. These lanes are opened in the direction with the highest demand in order to alleviate congestion as much as possible. The express lanes are operated on a weekday schedule and a weekend schedule. The schedule is sometimes changed to accommodate major events, construction work, and maintenance activities. 

The weekend schedule for the I-5 express lanes service is as follows:

· Southbound: 8:00 a.m. to 1:30 p.m.

· Northbound: 1:45 p.m. to 11:00 p.m.

The express lanes service is closed during the midday period from 1:30 p.m. to 1:45 p.m. so crews can safely reverse the direction of the express lanes. It is also closed overnight from 11:00 p.m. to 8:00 a.m. to reduce nighttime noise for residents near the Ship Canal Bridge.

Purpose of analysis

This study analyzes weekend traffic flow to determine whether the express lanes currently operate in the direction that will best accommodate traffic congestion during the weekend. It also evaluates whether the express lanes service appropriately serves traffic volumes on days with special events downtown such as concerts, Mariners, Sounders FC, or Seahawks games. 

Analysis data

Traffic data between June 2017 and December 2017 were used in this study. Days with and without major sporting events were included. The table below lists the dates used in the study. Days with sporting events were selected if they contained concerts, Mariners, Sounders FC, or Seahawks games that began between 12:00 p.m. and 7:30 p.m.



Although the report focuses on the overall results and the main factors that may affect operations, this express lanes study considered all of the following:

· Northbound and southbound volumes at multiple locations

· Northbound and southbound delay at multiple locations

· Overall congestion

· Access to and from the express lanes

· Demand for destinations serviced by the express lanes, and

· Alternative modes of transportation available


Traffic analysis

This traffic analysis evaluates total I-5 mainline volumes combined with express lanes volumes. The graphs shown use volumes just north of SR 520. At this location, the mainline has four lanes in each direction.


Saturday traffic volumes were studied separately from Sunday traffic volumes due to higher volumes on Saturdays.

Dates without major events were compared to dates with major events to evaluate the traffic impacts of the events.

I-5 volumes on Saturdays without major events

The graph below shows traffic volumes on Saturdays without a major event.

I-5 northbound traffic volumes peak at 6,000 vehicles per hour (vph) before the 1:30 p.m. express lanes transition. The northbound roadway is congested from approximately 10:00 a.m. until after northbound express lane service begins at 1:45 p.m. Throughput starts to decrease around 11:30 due to this congestion. Throughput remains fairly consistent after the transition at just under 8,000 vph until approximately 5:30 p.m.

On I-5 southbound, volumes increase up to 8,100 vph before the reversal of the express lanes. Just before the transition, volumes begin to decrease. After the transition, the roadway becomes congested as it is at capacity with 5,900 vph. The southbound roadway is congested until 7:00 p.m. when traffic volumes begin decreasing.



I-5 volumes on Saturdays with major events

The graph below shows traffic volumes on Saturdays with major events starting between 12:00 p.m. and 7:30 p.m.

I-5 northbound traffic volumes peak at 6,000 vph before the 1:30 p.m. express lanes transition. The northbound roadway is congested from 10:00 a.m. until 1:45 p.m. when the express lanes open in the northbound direction. Throughput decreases before the reversal due to the congestion. After the express lanes are opened in the northbound direction, volumes increase to about 8,000 vph and remain consistent until 5:00 p.m. Volumes spike again around 10:30 p.m. as people are leaving the event.

On I-5 southbound, traffic volumes increase to 8,600 vph before the express lanes reversal. Volumes begin to decrease just before the transition. Congestion forms when traffic volumes reach a capacity of 5,900 vph after southbound express lanes service ends at 1:30 p.m. Congestion typically last until 7 p.m. as volumes begin to decrease.
 

I-5 volumes on Sundays without major sporting events

The graph below shows traffic volumes on Sundays with no major event.

On I-5 northbound, traffic volumes are similar to a typical Saturday without major sporting event, and congestion forms when traffic volumes approaches a capacity of 6,000 vehicles per hour (vph) before the 1:30 p.m. express lanes transition. Throughput decreases slightly just before the transition due to the congestion. After northbound express lanes service begins, throughput peaks at 6:00 p.m. with 8,000 vph.

On I-5 southbound, volumes increase to about 8,000 vph between 10:00 and 12:00 a.m. Volumes decrease before the express lanes transition. The roadway becomes congested as it reaches its capacity of 5,900 vph after southbound express lanes service ends at 1:30 p.m. The southbound roadway is at its capacity until 7:00 p.m. when traffic volumes begin decreasing.



I-5 volumes on Sundays with major sporting events

The graph below shows traffic volumes on Saturdays with major events starting between 12:00 p.m. and 7:30 p.m.

On I-5 northbound, volumes peak at 6,000 vph. Congestion begins at approximately 11:30 a.m. and lasts until the express lanes are open in the northbound direction at 1:45 p.m. Throughput decreases due to the congestion. After northbound express lanes service begins, throughput peaks at 6:00 p.m. with 8,000 vph. Volumes quickly decrease after 6:00 p.m.

On I-5 southbound, Volumes reach about 8,000 vph at 10:00 a.m. Volumes remain consistent until about 12:30 p.m. when volumes start decreasing before the express lanes transition. Congestion forms after southbound express lanes service ends at 1:30 p.m. when traffic volumes reach a capacity of 5,900. congestion lasts until 7:00 p.m. when volumes begin to decrease.



Conclusion

The weekend traffic analysis shows that the express lanes transition currently occurs as southbound volumes begin to decrease and northbound congestion is increasing. This analysis shows that the express lanes operation should maintain the current schedule during the weekends.

There are no significant differences in volumes or congestion between weekend days with and weekend days without major events in downtown Seattle. The most notable difference is on days with a major event, there is a spike in northbound volumes at approximately 9:30 p.m. as people are leaving the event. This analysis shows that the schedule should remain the same for days with or without major events in the downtown area.

Extending the service of the express lanes in either direction does not benefit the overall transportation system and disadvantages one direction disproportionately. Therefore, in order to equally redistribute and alleviate congestion around Seattle down town area, it is not recommended that the express lanes schedule be modified at this time.

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