Keeping motorists apprised of changing traffic conditions and informing them of alternate routes ranked high in the Illinois DOT's (IDOT) goals during reconstruction of Interstate 70. The $74 million project called for rebuilding 10 miles of 33-year-old pavement, replacing or redecking five mainline bridges, raising and redecking five overhead bridges, reconstructing a rest area, and improving a weigh station.
Construction of the mainline portion of the project was placed on an expedited timetable, scheduled for completion in less than seven months. With daily traffic exceeding 21,000 vehicles, almost half of which were trucks, officials expected severe traffic delays during construction. To provide motorists with detailed, accurate, and timely information about construction progress and traffic conditions, IDOT proposed using an intelligent transportation system (ITS) for the project. The selected system, provided by United Rentals Highway Technologies, Greenwich, Conn., included portable solar-powered closed-circuit cameras, traffic sensors, a highway radio advisory system, citizens-band radio advisory equipment, and changeable message boards, linked by the latest wireless technology.
“The original intent was to inform the motorist of delays,” said Greg Idleman, IDOT District 5 project supervising construction engineer.” “However, the system was refined during construction to inform motorists of how they could bypass the construction zone.”
The ITS system employed various tools to collect information about traffic conditions, then sent that information to drivers, allowing them to avoid congestion and plan trips in advance. The collection system included both traffic sensors and surveillance cameras. The remote traffic microwave sensors (RTMS) could count individual vehicles within multiple lanes of traffic and report speeds ranging from 0 to 99 mph. Density and volume information from the sensors were sent to a central computer, which used an intelligent traffic algorithm and travel-time estimation model to calculate travel times and detect traffic queuing.
Other important data collection devices included portable, solar-powered, digital color cameras. These were equipped with remote pan, zoom, and tilt capability and were placed at various locations throughout the construction zone to monitor conditions. Both sensor and camera data were sent via wireless transmitters to a central computer system. Wireless technology permits quick setup and allowed the equipment to be placed in virtually any location within the construction zone.
Technicians used cellular digital packet data technology for communications though advanced mobile phone service; satellite communications also were available. Data were then sent to a central control computer, which continually collected the radar data, analyzed it, and—if a significant traffic slowdown was detected—automatically posted motorist warnings on the message signs and radio transmitters.
Message signs were placed at strategic locations to give travelers vital information while traveling at highway speeds. Messages were generated either from a pre-existing library or customized for the situation. Like the sensors and cameras, these signs were solar powered, wireless, and portable and could be easily relocated to suit changing jobsite conditions. Messages were sent automatically from a preprogrammed list (based on traffic speeds) and could advise motorists about taking alternate routes to avoid a particular situation.
Crews used highway advisory radio (HAR), along with variable message signs, to provide information. “The [HAR] system operated well.” said Scott Cornelius, IDOT District 5 project implementation engineer. “A standard message was looped 24 hours a day. In an emergency, IDOT could automatically invoke the HAR beacon along with a new message about an emergency detour if necessary.”
Installers placed local radio transmitters onsite with a broadcast range of 1 to 6 miles. These systems used the AM radio band and transmitted preprogrammed advisory messages, providing up-to-the-minute information on current traffic conditions, travel restrictions, detour routing, weather advisories, and construction updates. Both the changeable message signs and HAR were maintained from the central computer console and advised travelers about traffic conditions, including accidents and heavy congestion, lane closures, detours, and other condition information. Though messages were completely automated, a manual override permitted the addition of special motorist advisory messages to signs and HARs when needed.
All devices controlled by the central control system were continuously monitored. When an incident was detected, both traffic management and Illinois State Patrol operators were immediately notified of the problem. Travel advisories and incident details were then posted to the Web site, broadcast to HARs, and displayed on changeable message signs.