Another Busy Day In The Life Of I-90

Every day on our way to and from work, we all hit the same big curve: the statistical curve representing the flow of traffic on Valley roads.

This curve has lots of humps, bumps and potholes, but they tend to be predictable, and avoidable if your schedule is a little flexible.

Here’s a day in the life of that curve, as represented on Interstate 90 near Argonne on a recent Wednesday. (The numbers are provided by the Spokane Regional Transportation Council.)

At 3 a.m., the interstate is peacefully sleeping, and the traffic curve is flat, with just six or seven cars a minute tickling the roadbed.

Things start perking up from 5 to 6 a.m., with an average of 33 cars per minute humming by. Around the Valley, alarm clocks are ringing and coffee is brewing. Early birds are pulling onto the road and breathing life into the curve.

Each road in the Valley has its own little mini-curve that feeds into the overall hourly traffic pattern. Each one is synchronized to the beat of the workday clock.

At 6:30 on I-90 there are 82 cars per minute and climbing. Just before 7, the curve gets a little spike, up to 93 cars a minute, and then drops to 83 after 7.

Now the traffic curve is ready to romp and at 7:15 heads into the heart of the morning rush hour. For the next 60 minutes, an average of 100 cars per minute are zipping along.

From 7:30 to 7:45 is gut-check time for the curve, when it pumps about 116 cars per minute down the road.

After this strenuous workout, the curve relaxes at 8 a.m. As commuters knuckle down to work, it drops to a mid-morning rate of about 70 cars per minute.

After a little rest, sometime after 11, the curve starts a long, slow climb that it will sustain throughout the afternoon, heading for a climax during the evening rush hour.

From 1 to 2, it sees 82 cars per minute; from 2 to 3, there are 89 cars a minute.

Then at 3:30, the traffic curve takes a deep breath and hopes for the best. It breaks 100 cars a minute and is still on a steady climb. The peak afternoon traffic hour runs from about 4:30 to 5:30, when 110 cars per minute are caravaning along - hopefully. The average speed is far below the speed limit and any restrictions on lanes could bring it all to a halt.

The heart of the rush hour is just after 5, but it doesn’t really slack off until after 6. By 7, the excitement is over and the evening pace of about 40 cars per minute slowly shrinks into the night.

The traffic curve has a chance to recuperate and get ready for tomorrow’s cycle.

Plan ahead for delays

The Spokane Regional Transportation Council’s traffic model on planner Ken Decker’s computer is able to calculate transit times from any two points in the Spokane area. And he can do it for today, 2010, and 2020. The fastest route from downtown to Sullivan Road (guess what, it’s I-90) currently takes about 18.8 minutes at peak time. In 2010, even with planned road improvements, it will take 21.3 minutes and in 2020, 22.5 minutes, according to the model. So you might warn your spouse that, in the future, you’ll be a little late.

, DataTimes MEMO: On Your Way is a Valley Voice column focusing on commuter lifestyles and issues. Your views on any of the topics discussed are invited. Please write: On Your Way, The Valley Voice, 13208 E. Sprague, Spokane, WA 99216. Fax us at 459-5482 or call Jim Springer at 459-5441.