One of the responsibilities of the Des Moines Area Metropolitan Planning Organization is to monitor and report on interstate highway traffic patterns. This data is used to build a long-range transportation plan based on traffic and trip projections.
The Business Record recently published an article analyzing 2009 MPO data (PDF report) that contained a table with morning and evening commute data between downtown and the western junction of I-235 and I-35.
Stick with me through this analysis - am I reading this data right?
The distance from Downtown to the the I-35 junction is 8.3 miles. Of that segment, approximately 5.5 miles is posted at 60 MPH and 2.8 is posted at 55 MPH. Therefore, the legal minimum amount of time it takes to drive from downtown to the western junction is (5.5/60)+(2.8/55)=.143 hours or 8.55 minutes.
Because 8.55 minutes is the fastest one can legally drive the segment of I-235 between downtown and the western junction, I'm going to refer to this as the "legal posted minimum" travel time.
According to the MPO data as presented by the Business Record, Des Moines doesn't really have a rush hour.
Actual measured average travel time over this segment only exceeds the legal posted minimum travel time between 7:45 and 8:15 am in the eastbound lanes and between 5:00 and 5:45 pm in the westbound lanes.
It gets even better!
According to the Business Record analysis, the average difference in commute time between the actual measured and the legal posted minimum is a minuscule 15 seconds! In other words, if you drive legally and safely even when you can speed, your commute between the western suburbs and Downtown Des Moines will average only 15 seconds longer during "rush hour".
Of course the speed data also includes those people that put the pedal to the metal once they have an opening in traffic. And, during non-rush hour times, the average speed across the entire segment is above the posted limit. In some areas, significantly above.
Breakin' the Law!
Discussing the data, the Business Record said:
Your absolute best option - if your bosses will allow it - is to get on I-235 at about 7 a.m. and go home at about 4 p.m. Over the course of time, you could save three minutes per day on average. That might not sound like much, but translate that over the course of 10 years, and you can save upwards of five days of your life.
Actually, this is only true if you break the law.Continue reading...