Skip Top Navigation

I-5 Express Lane Operation on Weekends

December 18, 2015

Express lanes concept

The Washington State Department of Transportation uses express lanes on I-5 and I-90 to improve traffic flow during peak travel times. 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.


Purpose of analysis

This study analyzes weekend traffic flow to determine whether the express lanes operate in the direction that will best accommodate traffic congestion during the weekend.


Analysis data

Traffic data between June 2014 and November 2014 were used in this study. Days with and without major sporting events were included. Figure 1 below lists the dates used in the study. Days with sporting events were selected if they contained Husky football, 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
- Northbound and southbound delay
- 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 mainline volumes combined with express lanes volumes. The study was conducted at Mercer St for northbound and NE 45th St for southbound. The mainline has four lanes in each direction.

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

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


I-5 volumes on Saturdays without sporting events

(Figure 2 below shows traffic volumes on Saturdays with no major sporting event)

On I-5 northbound, congestion forms at Mercer Street when traffic volumes reach a capacity of 7,000 vehicles per hour (vph) before 1:30 p.m. express lanes transition. The northbound roadway is at capacity from approximately 11:00 a.m. until 1:45 p.m. After northbound express lanes service begin, throughput peaks at 3:35 p.m. with 9,100 vph. 

On I-5 southbound, the roadway becomes congested as it reaches its capacity of 6,500 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 Saturdays with sporting events

(Figure 3 below shows traffic volumes on Saturdays with major sporting events starting between 12:00 p.m. and 7:30 p.m.)

On I-5 northbound, congestion forms when traffic volumes reach a capacity of 7,000 vph. This begins at approximately a half an hour before typical Saturday at 10:30 a.m. and lasts until the express lanes are open in the northbound direction at 1:45 p.m.

On I-5 southbound, congestion forms when traffic volumes reach a capacity of 6,000 vph after southbound express lanes service ends at 1:30 p.m.

 



I-5 volumes on Sundays without major sporting events

(Figure 4 below shows traffic volumes on Sundays with no major sporting 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 7,000 vehicles per hour (vph) before the 1:30 p.m. express lanes transition. After northbound express lanes service begins, throughput peaks at 1:45 p.m. with 9,000 vph.

On I-5 southbound, the roadway becomes congested as it reaches its capacity of 6,400 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

(Figure 5 below shows traffic volumes on Sundays with major sporting events)

On I-5 northbound, congestion forms when traffic volumes reach a capacity of 6,000 vph. This begins at approximately a half an hour before typical Sunday at 10:30 a.m. and lasts until the express lanes are open in the northbound direction at 1:45 p.m.

On I-5 southbound, congestion forms when traffic volumes reach a capacity of 6,500 vph after southbound express lanes service ends at 1:30 p.m.



 

Traffic Analysis - Saturdays


Drivers on I-5 experience heavy congestion when traffic volumes exceed a capacity of approximately 7,000 vph for northbound and 6,500 vph for southbound when the express lanes are closed in a direction of travel.

On Saturdays with major sporting events, northbound congestion begins approximately at 10:30 a.m., a half an hour earlier than a typical Saturday, and lasts until 2:45 p.m., an additional hour than typical Saturday. There are no significant differences in southbound congestions between Saturdays with or without major sporting events.

As shown in Figure 6 and Figure 7 below, a similar pattern can be seen for Saturdays without major sporting events, during which the express lanes are open in the direction with the higher volumes.


Traffic Analysis - Sundays


As similar to Saturdays, drivers on I-5 experience heavy congestion when traffic volumes fluctuate near capacity of 7,000 vph for northbound and 6,500 vph for southbound while the express lanes are closed.

On Sundays with major sporting events, northbound congestion begins approximately at 11:00 a.m., a half an hour earlier than a typical Sunday, and lasts an additional half an hour after the express lanes are open in northbound direction at 1:45 p.m. There are no significant differences in southbound congestions between Sundays with or without major sporting events.

As shown in Figure 6 and Figure 7 below, a similar pattern can be seen for Sundays without major sporting events, during which the express lanes are open in the direction with the higher volumes.






Conclusion


The weekend traffic analysis shows that the express lanes operation should maintain a current schedule during the days with or without major events in Seattle down town area.

Traffic volumes increase in both direction of I-5 on game days. 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.