While Iowa’s interstates make up a fraction of the state’s overall roadway miles – just 0.7 percent of the system – it has an outsize representation in its usage. Iowa’s interstates support 25 percent of vehicle miles traveled and 56 percent of large-truck vehicle miles.
That means the Iowa Department of Transportation (DOT) has an outsize interest in ensuring drivers can traverse the interstates as safely and efficiently as possible.
Engineers at Iowa State University’s Institute for Transportation (InTrans) and its REACTOR Lab worked with the Iowa DOT’s Office of Traffic Operations to put together a report to understand and assess the impact of Interstate congestion, which is defined as speeds dropping below 45 miles per hour.
The 2016 Interstate Congestion Report, which documented Iowa’s interstate travel during the 2016 calendar year, offered some interesting insights, including:
- Excessive Congestion costs totaled $27.9 million on Interstates in 2016.
- Peak congestion occurs during the month of June, during Fridays, and during the time of day of 5 to 6 p.m.
- Sources of congestion include recurring events, like daily commuter congestion or capacity restrictions, and non-recurring events, like traffic incidents, work zones, and weather.
- On a per mile basis, Polk and Scott counties had the highest costs of delay, with construction being part of the congestion in the latter county.
InTrans’ work with the Iowa DOT is ongoing to better understand Iowa’s traffic congestion. In the future, the information will also be shared with transportation groups, like metropolitan planning organizations.
The Iowa DOT plans to use the information gathered by the report to improve decision-making, readiness, and investment on these important roadways.
This becomes more challenging as there is increased demand put on the system. Iowa’s most-traveled interstate for freight truck traffic is I-80, with 435 million tons of freight carried in 2010; it’s anticipated to increase to 620 million tons within 30 years.