Office of Operations
21st Century Operations Using 21st Century Technologies

Travel Time Messaging on Dynamic Message Signs - Chicago, IL

Illinois State Toll Highway Authority

May 2005

Table of Contents

1.0 Introduction
2.0 Deployment Information
3.0 System Planning and Development
4.0 Data Collection and Processing
5.0 Travel Time Messaging
6.0 Relationships With Other Agencies/Stakeholders
7.0 Public Outreach and Impacts
8.0 Issues Faced and How They Were Resolved
9.0 Contacts

1.0 Introduction

Originally designed and developed as a bypass around the Chicago Metropolitan area, the Illinois State Toll Highway Authority is today a primary interstate transportation system for the northern Illinois area. Its 274 centerline mile system of toll roads includes:

  • I-294 Tri-State Tollway, extending from Indiana to Wisconsin
  • I-90 Northwest Tollway, extending from the western limits of Chicago to Wisconsin (through Rockford);
  • I-88 East-West Tollway, extending from the Tri-State Tollway to Rock Falls, Illinois, forty-four miles from the Mississippi River
  • I-355 North-South Tollway, extending north seventeen miles from I-55 Stevenson Expressway.

The Greater Chicago metropolitan area contains some of the most congested section of roadway in the country, with traffic increasing annually. In response, ISTHA has adopted a strategy of providing real time information to its customers, especially at decision points, about their travel to and from Chicago.

2.0 Deployment Information

ISTHA began providing average travel times from toll plaza to toll plaza based on IPASS toll transponder data collected by its Electronic Toll Collection (ETC) system (see Figure 1). The automated IPASS toll collection system was implemented in 1993 and its users now number in excess of 1.5 million. This large number of users provides the Tollway with a significant penetration of vehicle probes, providing time-stamped location information to the Tollway in near real-time. This probe-based information is of a high quality because of IPASS system design requirements related to the support of monetary transactions. The data is used to calculate travel times using Origin and Destination location and time-stamp information. IPASS identification information is discarded and no individual vehicles are tracked by the system1.

Image of Figure 1 – IPASS Transponders
Figure 1 - IPASS Transponders

In addition to ETC data from IPASS transponders, data from RTMS (radar sensor) stations along the Tollway provide additional traffic and speed data to support the calculation of travel times. These RTMS stations are owned and operated by a private vendor as part of the USDOT's Intelligent Transportation Infrastructure Program (ITIP). Locations of the RTMS are shown in Figure 2. Data from the Illinois DOT's (IDOT) loop detector network is also used to calculate travel time estimates for sections of IDOT roadway leading to/from Tollway facilities.

Image of Figure 2 – Location of RTMS Units (represented by dots in figure)
Figure 2 - Location of RTMS Units (represented by dots in figure)

Travel times are calculated using a combination of IDOT loop detector, RTMS, and IPASS data. ISTHA currently posts travel times onto 21 DMS located on Tollway and nearby Illinois DOT roads, with another 12 DMS to be deployed by May, 2005. All DMS are connected to a fiber optic network and controlled from a central location - the Traffic and Incident Management System (TIMS) Traffic Operations Center. The TIMS center has two full-time technicians (working in shifts) who manage the software system that controls the posting of all DMS messages including: incident management, amber alerts, and travel time messages. Two additional full-time employees and two part-time employees will eventually be added to support ISTHA expansion plans, including the operation of new DMS.

All staff are cross-trained to perform numerous TIMS center functions.

3.0 System Planning and Development

In the mid-1990s, ISTHA constructed a new integrated traffic operations center and deployed a system of electronic toll collection. These deployments allowed for more extensive traffic management capabilities and enabled the calculation of travel times.

Increasing congestion forced ISTHA to investigate new traffic and incident management strategies for ISTHA facilities. ISTHA officials visited traffic management centers in Atlanta, Seattle, San Antonio, and Toronto to gather information concerning traffic management. As a result of this research, ISTHA elected to integrate much of its traffic management functionality into a single operations center - the Traffic and Incident Management System Traffic Operations Center (TIMS TOC) (See Figure 3. The TIMS TOC was also integrated into the Computer Aided Dispatch System operated out of the Central Dispatch Center that provides for both public safety and incident management dispatching 24/7. In addition to facilitating the seamless sharing of traffic-related information, integration of these two systems also allows the Tollway to efficiently operate its TOC without separate staffing during overnight and weekend hours.

The two primary functions of the TIMS TOC were to comprehensively manage traffic and incidents, and to provide travelers with road condition information in an effective manner.

Image of Figure 3 – The TIMS Traffic Operation Center
Figure 3 - The TIMS Traffic Operation Center

The ability to provide travel times was a direct result of implementation of the Electronic Toll Collection system which provided ISTHA with a source of travel time data. Implementation of ETC allowed ISTHA to efficiently collect near real-time system data while bypassing traditional means of vehicle detection (e.g., loop detectors).

Early on, it was determined that travel time data derived from toll transponders was very accurate during free flow conditions, but that this data lagged when traffic was in a transition stage (e.g., free flow conditions becoming more congested, incidents, etc). To address this problem, ISTHA investigated deployment of RTMS (radar) sensors as part of the USDOT's ITIP program. The agency subsequently applied for and obtained ITIP funding. As part of this program, a private vendor installed and operates RTMS sensor sites along large portions of the Tollway2. With the deployment of these additional sensors and the provision of their raw speed data, ISTHA has improved the quality of their travel time estimates. The increased granularity of data from the RTMS Sensors has also allowed ISTHA to develop incident detection algorithms that will assist in pinpointing when and where incidents occur.

ISTHA believes that their travel time system is now close to maturity in urban and suburban portions of the Chicago metropolitan area, with outlying areas still requiring deployment of either RTMS or interim IPASS tag readers.

The current DMS messaging system is providing drivers with useful information and improving the overall system operations. Customer satisfaction with the DMS is also enhanced. These results have led to a current push to expand the DMS system.

4.0 Data Collection and Processing

Three sources of data are currently used by ISTHA to provide travel time estimates:

  • I-PASS readers at toll plazas.
  • Data from the IDOT loop detector network - to generate travel time estimates for non-Tollway roads in downtown Chicago.
  • ITIP RTMS data

The travel time system organizes the toll network into roadway segments, which represent the finest resolution for which data will be provided; roadway segments are typically bounded by ramps and mainline plazas. Lengths of segments vary across the Tollway (shorter near Chicago, but longer in outlying areas). The IPASS and RTMS data provide a level of redundancy for along certain segments of the toll system (i.e., there may be two sources of travel data for a particular section). ISTHA's travel time software allows the TIMS staff to choose which data source should be used in a given situation. Decisions are made by TIMS staff based on operational experience and judgment. For other segments, only one source of speed data is available (i.e., a segment may have only an RTMS station).

Segment-specific travel time data is then analyzed by ISTHA's travel time software at the TIMS Center to generate a travel time to a target destination from each DMS3. A travel time estimate to a target destination might include segments for which travel time has been determined using any one of the three sources of data. Travel time updates are currently posted to the DMS every 3 minutes, with the goal being to eventually post updates every minute. Figure 4 shows the travel time posting screen an operator views in the TIMS software.

Accuracy of travel time estimates has been a concern for ISTHA from the beginning of the project. During the early stages of system deployment, video observations of traffic flow were compared with the TIMS software's travel time estimates to provide reasonable assurances that the information was accurate. ISTHA also directed their on-call consultant to conduct a probe-vehicle travel time test to measure the accuracy of the travel times provided by their algorithm. The results of this test indicated that the travel times produced by the system were sufficiently accurate for release to the public. System operators conduct no ongoing reviews of data quality unless obvious discrepancies occur. However, data quality is checked annually using probe vehicles.

Image of Figure 4 – Travel Time Posting Screen – TIMS Software
Figure 4 - Travel Time Posting Screen - TIMS Software

5.0 Travel Time Messaging

Initially, DMS were used to provide motorists with incident and construction information and would remain blank when such information was not available. After a few months, the Tollway began posting travel time messages4. Travel Times are posted from 5:00-10:00 AM, 3:00-7:00 pm, and after incidents.

Travel time information is provided in one of two formats, depending on the number of destinations for which travel time information is to be displayed. This information is right justified for ease of reading by drivers (see Figure 5).

Incident related messages have the highest priority for posting to the DMS. Amber alerts and non-incident related road closures are next in priority, followed by travel time messages. Generic safety messages are last on the priority list of DMS messages. No messages are posted to the DMS in instances where data quality is questionable. ISTHA's traffic management center fields calls from commuters who let them know when they perceive that travel times are incorrect.

Image of Figure 5 - Travel Times on DMS
Figure 5 - Travel Times on DMS

6.0 Relationships With Other Agencies/Stakeholders

ISTHA has a detailed agreement with Mobility Technologies for use of the ITIP data in the travel time algorithm5. ISTHA's travel time and congestion information is provided to the public via the Gary-Chicago-Milwaukee (GCM6) Gateway website, from which the public can access near-real time traffic information on ISTHA and IDOT roadways (see Figure 6). ISHTA also shares real-time traffic information with IDOT on adjoining facilities.

Only IPASS travel times calculated through the use of IPASS tag readers are sent to the GCM website; contractual restrictions prevent ISTHA from publishing ITIP data on the GCM site. This results in there being a slight deviation in the information posted to the DMS versus that posted to the GCM website. 

Image of Figure 6 – Chicago Travel Time Information on the Internet
Figure 6 - Chicago Travel Time Information on the Internet

7.0 Public Outreach and Impacts

Feedback concerning ISTHA's travel time data has been extremely positive. Tollway representatives believe that the provision of this data causes drivers to modify their behavior and helps to ease motorist frustrations by providing a reasonable expectation of what will be encountered on Tollway roads.

Although ISTHA has not conducted a formal study, they are aware (through customer emails and calls to the customer input line) that users do not like other messages being posted onto the DMS in place of travel time information. Often when a non-incident related message is posted during a time at which travel time information is normally posted, ISTHA will receive negative feedback from drivers.

ISTHA's travel time system has also received coverage in the Chicago Tribune newspaper7. The report provided press coverage of ISTHA's system and mentioned its ability to allow drivers to make more informed choices.

8.0 Issues Faced and How They Were Resolved

Issue Resolution
Initial reluctance to install DMS signs One of the issues was that DMS were previously blank most of the time; posting of travel times during peak periods and after incidents has greatly increased the visibility of the DMS network
Problems using IPASS transponders over long segments prone to congestions, or during incidents Deployment of RTMS sensors has greatly increased the granularity of the system and enabled highly reliable estimates of travel time. ISTHA is planning to deploy interim IPASS readers to fill in gaps in existing coverage, as well as on segments in outlying areas. Increasing the granularity of the system by increasing the density of IPASS tag readers will help increase the accuracy of probe-based travel times during more congested conditions.
Staffing of TOC As the number of DMS increases, the demands placed on TOC operators will increase as well. ISTHA has cross trained its staff to be able to manage turnover and staff absences. While better documentation of training procedures is still needed, ISTHA believes that cross-training of staff has met an essential need.
System maintenance ISTHA has maintenance agreements with the developer for the TIMS software; the IPASS system is maintained by TransCore; RTMS stations are maintained by Mobility Technologies. These maintenance agreements have helped ISTHA focus on its core mission.
Multiple data sources Some segments have multiple sources of information (RTMS data from a private vendor, IPASS, and IDOT loop detector data). Operational judgment is required to determine which data stream(s) should be used to develop travel time estimates for a particular segment. ISTHA's TIMS software developer and overall systems integrator has been able to fuse segments using different sources of data to generate travel times.
Restrictions on use of private sector data Although the travel times posted onto the DMS can be calculated based on data from IPASS tags, ITIP RTMS units, and data received from IDOT, only IPASS-based travel times are sent to the GCM web page. Contractual restrictions prevent ISTHA from publishing ITIP data on the GCM - this results in a slight deviation of information between what is posted to the DMS versus what is posted to the GCM website. To overcome this issue, ISTHA plans to deploy more interim tag readers for the purpose of improving IPASS-based travel time estimates.

Lessons Learned

  • Accuracy is very important to travel time messaging. ISTHA hears from commuters if they feel that travel time messages are incorrect.
  • Deployment of DMS should be prior to key decision points where commuters can decide to take alternate routes. Understanding the commuting patterns in the region when planning locations for DMS deployment is important.
  • Using DMS for travel time messaging increases their visibility and helps justify the deployment.

9.0 Contacts

John Benda, ISTHA,
Ken Glassman, ISTHA,
Abby Malloy, ISTHA,

Image Credits: All Images in the case study are from ISTHA and Ken Glassman's ITS America Paper

1Glassman et al, The Use of IPASS to Improve Mobility and Safety Through Traveler Information, Prepared for ITS America, 2003

2Mobility Technologies owns and maintains the RTMS units in the Tollway facilities. They collect, process and distribute this data to various sources including several media outlets in the Chicago area.

3The TMC software was developed by ISTHA's system integrator, National Engineering Technology Corp. (NET)).

4Glassman et al, The Use of IPASS to Improve Mobility and Safety Through Traveler Information, Prepared for ITS America, 2003

5ISTHA can use the data for posting travel times on DMS, but has to be careful about protecting its proprietary nature [i.e., ISTHA cannot provide this data to any users (e.g., private firms) for resale.

6The GCM Intelligent Transportation System (ITS) Priority Corridor is one of four multi-agency ITS coalitions formed as a result of the Intermodal Surface Transportation and Efficiency Act of 1991 (ISETEA). Officially started in 1993, the GCM Corridor is comprised of all of the major transportation agencies in the 16 county area connecting Gary, Indiana through Chicago, Illinois to Milwaukee, Wisconsin.

7Toll agency now posting drive times: Motorists can get instant updates, By Jon Hilkevitch, Tribune transportation reporter, Published March 17, 2003

Federal Highway Administration
U.S. Department of Transportation
400 7th Street, S.W. (HOP)
Washington, DC 20590
Toll-Free "Help Line" 866-367-7487
Publication Number: FHWA-HOP-05-049

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