Posted on July 13, 2010 7:23 AM
2009 Chicago Region Freeway Performance Measures
As part of the CMAP Congestion Management Process, staff has compiled performance measures for the regional freeways for 2009. The performance measures include congestion scans, travel time index, planning time index, and congested hours. Congestion scans show average speed by milepost by time of day for the freeway segment.
The travel time index is a measure of average congestion and indicates the average extra travel time required during peak period congestion. Travel time index is a ratio of the average peak period travel time compared to the free-flow travel time. For example, a value of 1.20 means that average peak travel times are 20 percent longer than free-flow travel times.
The planning time index is a measure of reliability. The planning time index is defined as the ratio of the total time needed to ensure a 95percent on-time arrival to the free-flow travel time. For example, a value of 1.4 means that, to arrive on-time 95 percent of the time, a traveler should budget an additional 8 minutes for a trip that takes 20 minutes during off-peak, free-flow conditions.
Congested hours are an indication of how many hours per day a facility is congested. Technically, "congested hours" are defined as the average number of hours in which at least 20 percent of the vehicle miles traveled (VMT) on the instrumented segment is congested. For this measure, congestion is defined to occur when link speeds are less than 50 mph.
Chicago region freeway performance measures are available on the CMAP website.
| I-290 from Canal St. to Wolf Rd. 2009 congestion scan. |