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I-5 Express Lane Operation on Weekends

July 10, 2013

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. These lanes are opened in the direction with the highest demand. 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 reduce traffic congestion during the weekend.


Analysis data

Traffic data between July 2012 and December 2012 were used in this study. Days with and without major sporting events were included. Figure 1 below lists the dates used in the study with and without major sporting events. 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 1:10 p.m.



Figure 1:  Dates used for analysis, July 1, 2012 – December 1, 2012


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 without sporting events.
On I-5 northbound, traffic slows down on at Mercer St when traffic volumes reach a capacity of 7,000 vehicles per hour (vph). The northbound roadway is at capacity from approximately 10:30 a.m. until 12:30 p.m. Northbound throughput peaks at 4:15 p.m. with 9,300 vph.

On I-5 southbound, the roadway becomes congested as it reaches its capacity of 6,500 vph. This begins when the I-5 southbound express lanes service ends at 1:30 p.m. The southbound roadway is at capacity until 6:30 p.m. when traffic volumes begin decreasing. Southbound throughput peaks at 12:30 p.m. with 8,900 vph.


Figure 2:  I-5 directional hourly volumes on Saturdays without major sporting events




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 1:10 p.m.

On I-5 northbound, traffic slows down when traffic volumes reach a capacity of 7,000 vph. This begins at approximately 10:30 a.m. and lasts until the express lanes are open in the northbound direction at 1:45 p.m. Northbound throughput peaks at 3:45 p.m. with 10,000 vph, which coincides with the conclusion of the sporting events.

On I-5 southbound, traffic slows down when traffic volumes reach a capacity of 6,500 vph. This begins at 1:30 p.m., when the southbound express lane service ends, and lasts until 7:00 p.m., when both demand and throughput begin decreasing. Southbound throughput peaks at 11:30 a.m. with 9,600 vph. 


Figure 3:  I-5 directional hourly volumes on Saturdays with major sporting events




I-5 volumes on Sundays without major sporting events

Figure 4 below shows traffic volumes on Sundays without major sporting events.

On I-5 northbound, traffic slows down when traffic volumes approaches a capacity 7,000 vehicles per hour (vph). Congestion is moderate due to the high fluctuations in volume nearing capacity. This begins at approximately 12:15 p.m. and lasts until 1:45 p.m. Northbound traffic volumes peak at 4:15 p.m. with 9,000 vph.

On I-5 southbound, traffic remains at free-flow speeds until the southbound express lanes service closes at 1:30 p.m. Congestion begins at 1:30 p.m. and lasts until 6:15 p.m., when traffic volumes decrease below 6,500 vph. Southbound traffic volumes peak at 12:45 a.m. with 8,000 vph.


Figure 4:  I-5 directional hourly volumes on Sundays without major sporting events


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, traffic slows down when traffic volumes exceed 7,000 vph. This begins at 11:40 p.m. and lasts until 1:45 p.m. Northbound traffic volumes peak at 4:30 p.m. with 10,600 vph.

On I-5 southbound, the roadway becomes congested as it reaches a capacity of 6,500 vph. This begins when the I-5 southbound express lanes service ends at 1:30 p.m. Congestion persists until 6:45 p.m., when traffic volumes decrease at a faster rate. Southbound traffic volume peaks at 11:45 a.m. with 8,700 vph.



Figure 5:  I-5 directional hourly volumes on Sundays with major sporting events

 

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.

On Saturdays without major sporting events, there is heavy northbound congestion from 10:30 a.m. to 12:30 p.m. and heavy southbound congestion from 1:30 p.m. to 6:30 p.m.

On Saturdays with major sporting events, northbound congestion begins at the same time as typical Saturday, but lasts for an additional 1 hour and 15 minutes. Southbound congestion lasts for an additional 2 hours on Saturdays with major sporting events.

With the express lanes service open southbound from 8:00 a.m. to 1:30 p.m., approximately 8,800 more vehicles travel southbound than northbound on Saturdays with major sporting events.

With the express lanes service open northbound from 1:45 p.m. to 11:00 p.m., approximately 18,400 more vehicles travel northbound than southbound on Saturdays with 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

On Sundays without major sporting events, moderate congestion develops northbound from approximately 12:15 p.m. to 1:45 p.m. as volumes fluctuate near capacity of 7,000 vph. Southbound congestion typically lasts from 1:30 p.m. to 6:15 p.m.

On Sundays with major sporting events, northbound congestion begins approximately 30 minutes earlier at 11:45 a.m. Also, congestion is heavier than typical Sundays because once the roadway reaches capacity; throughput does not increase as shown by the steady horizontal line in Figure 5. Approximately an hour before the start of the major sporting event, there is a spike in demand as shown by the dip at 6:00 p.m. in Figure 5. This southbound congestion does not dissipate until 6:45 p.m., 30 minutes later than a typical Sunday.

With the express lanes service open southbound, 7,000 additional vehicles travelled southbound than northbound on Sundays with major sporting events.

With the express lanes open northbound, 19,700 additional vehicles travelled northbound than southbound on Sundays with major sporting events.

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



Figure 6:  I-5 total volumes during southbound express lanes service



Figure 7:  I-5 total volumes during northbound express lanes service



Conclusion

The weekend traffic analysis shows that the express lanes schedule responds to peak traffic volumes. The express lanes service is southbound when southbound traffic volumes are at their highest and northbound when northbound traffic volumes are at their highest.

The analysis shows that the current express lanes schedule appropriately serves the direction with the highest demand. Therefore, it is not recommended that the express lanes schedule be modified at this time.