Based on favorable experience with intelligent transportation systems (ITS) on other projects, the Illinois Department of Transportation (IDOT) decided to use ITS in a 40-mile work zone for the major bridge and highway reconstruction along I-55 south of Springfield. The ITS, referred to as the Real-Time Traffic Control System (RTTCS), consisted of 17 remotely-controlled portable dynamic message signs (DMS), eight portable traffic sensors, and four portable cameras linked to a base station server via wireless communication. The RTTCS covered the work zone area as well as the northbound and southbound approaches to the work zone.

The traffic sensors used X-Band radar to automatically collect vehicle speed and presence data which was transmitted to the central base station server. The central server calculated volume and traffic speed and generated predetermined messages based on the level of traffic congestion. Real-time traffic conditions such as delay information and lane closure advisories were automatically transmitted and displayed on the portable DMS and IDOT’s website. The system updated the website every five minutes based on congestion levels in the work zone. IDOT staff was automatically notified of congestion and incident detection alerts. Images from the portable cameras were used to confirm data generated by the system. Solar arrays provided power source for the battery-operated roadside equipment.

The RTTCS was designed based on IDOT staff developing a set of functional requirements and then comparing the approach proposed by the vendor. After finalizing the system design, the resulting system was leased by the prime contractor from a firm specializing in work zone systems. IDOT indicated significant cost savings by leasing the RTTCS as a bid item. The cost of leasing the system was $785,000 which represented approximately 2 percent of the total reconstruction contract cost of $35 million. The system was deployed for a total of 16 months from February 2001 to May 2002.

The lease included a provision for contractor personnel to monitor the system and provide 24-hour maintenance support. The system operated in an automatic mode; however, one person was assigned to check system performance periodically during week days. After hours and during weekends, contractor personnel were on-call to handle problems. The terms and conditions of the lease agreement stipulated fines for system deficiencies if not corrected within a specified time.


See Also: the system cost summary for Intelligent Transportation Systems in Work Zones – A Cross Cutting Study