Freeway Management and Operations Handbook

Description of Figure 4-4: The Effect of Ramp Meters on Vehicle Volume (per lane) Throughput and Frequency of LOS F Operations

This graph shows volume and congestion on Eastbound SR-520 on the viaduct. It shows the frequency of congestion on the left vertical axis, ranging from 0 to 90. Time of day is shown on the horizontal axis, ranging from 5:30 AM to 7:30 PM. Hourly volume per lane is shown on the right vertical axis, ranging from 0 to 2,000 vehicles.

Two histograms (depicted as vertical bars) and two volume plots (depicted as curved lines) are shown: one each for 1999 (before ramp metering was used during the AM) shown in blue, and one each for 2001 (after AM ramp metering was implemented) in red. The blue and red curved lines for 1999 and 2001, respectively, show that volume peaked near 6 AM for both years, but with an improvement of 170 vehicles per hour per lane. The blue and red vertical bars for 1999 and 2001, respectively, show that congestion peaked between 7:30 AM and 8:00 for both years, but a note states that "LOS F occurs 1 day per week less often".