The Michigan Department of Transportation (MDOT) predicted major congestion during the 2007 total closure of the Lodge Freeway (M-10), a primary commuting route between downtown Detroit and the northwestern suburbs of Detroit. The $139 million Lodge project closed 10 miles (Lahser to I-94) of the Lodge Freeway for five months (April through August 2007) and was one of MDOT’s largest projects in recent years.
To improve mobility in metro Detroit, MDOT deployed a real-time work-zone information system (RTWS). The goal of an RTWS is to deliver real-time traffic information to motorists so they can make decisions before and along detour routes to avoid traffic congestion.
MDOT is proving to be a leader in the national struggle to increase work-zone mobility. The RTWS is leading the way toward compliance with the Federal Highway Administration (FHWA) Final Rule for Work Zone Mobility. For Michigan, the system is already in place and was set to be enforced beginning in October 2007. MDOT’s metro region initially designed and deployed an RTWS in 2005 for a ramp-widening project that affected a stretch of traffic on I-275. In 2006, metro region systems used “delay” times through two major work zones along M-14 and at the M-10/I-696 interchange. These delay-time systems targeted mobility exclusively. The 2007 system on the Lodge encompasses the entire metro region and provides a travel-time system.
MDOT expanded the use of RTWS on the Lodge project as compared with previous projects. MDOT will further expand use of RTWS when it begins work on an I-75 freeway reconstruction project (Gateway) at the Ambassador Bridge border crossing between the U.S. and Canada. The Gateway project is a three-year, $180 million project that will maintain access to the Ambassador Bridge during construction.
MDOT also is setting its sights on having a permanent travel-time RTWS for specific freeways in the metro region within the next two years. Currently, MDOT uses a less accurate means of estimating travel times along certain freeways.
The basics
The basic aspects of the Lodge RTWS include traffic sensors, portable changeable message signs (PCMS), dynamic message panels (DMP), portable cameras and website access to monitor and control messages 24/7. The traffic sensors are nonintrusive off-road. The sensors’ accuracy is not degraded by inclement weather or poor visibility including precipitation, fog, darkness or excessive dust. The Lodge project uses three unique sources of traffic detection:
- Portable Doppler detectors are measurably more accurate and reliable for speed data;
- Portable remote traffic microwave sensors offer volume data and multilane detection, which delivers better performance for locations with larger speed differential between lanes; and
- MDOT’s permanent infrastructure of loop sensors gives the system better depth at a lower cost and faster deployment.
The contractor and the MDOT control room in Detroit have access to manually override the motorist information messages on the PCMS. All of the DMP are static signs describing the destination with an electronic display for travel time. This two-digit display offers a clear and concise method to convey the pertinent travel-time information. Where a weekend lane closure or a single day closure would normally use PCMS, in this application the signs are placed in a single location for several months, so many more DMPs were used for clarity, efficiency and readability instead of the PCMS.
Of the 24 DMPs for the project, MDOT chose to use only four automated PCMS, which hold drivers’ attention for a much longer time and only deliver a small component of dynamic information. Regular commuters get to know the sign after the first or second viewing so there was no reason to flash a full PCMS message for the entire project length when the only dynamic component of the information was the travel time itself. The automated PCMS devices were strategically located to be used as message signs for alternative routes and other emergency messaging.
The pan-tilt-zoom (PTZ) cameras are portable and can be moved to strategic locations for specific phases of the project where permanently mounted MDOT cameras are not available. These portable cameras can be moved by the contractor and MDOT to optimize the most beneficial view.
The operator website access provides current operational status, historical volume and speed data and the ability to recognize malfunctioning equipment. The website provides an overall view of the RTWS network where signs, cameras and sensors may be chosen to monitor status.
Performance
Personnel are notified via e-mail when a malfunction has occurred in the system, and the contractor is required to make the necessary repairs within 72 hours. Failure to repair the system within the allotted time will result in a 5% reduction in the unit price of the contract item.
Twice during the first half of the live RTWS project, MDOT sensors became inoperable for several days due to inadequate detection and caused misinformation on the DMP. Additional temporary sensors were deployed to prevent future misinformation in the event the MDOT loop sensors malfunctioned again. MDOT deactivated the DMP when information was inaccurate.
The RTWS portion of the project was supported by an additional 29 standard PCMS, allowing MDOT and the contractors to revise messages remotely from a laptop computer to provide motorists information other than travel-time information. MDOT attempts to revise PCMS messages every two weeks to keep information fresh and motorists alert and focused on reading the information.
The specialty contractor, Traffic Technologies of Minneapolis, augmented the portable sensor deployment with MDOT’s permanent infrastructure of loop sensors. MDOT’s permanent loop sensors are typically spaced at 2 miles. Currently, MDOT installs permanent sensors at 1-mile intervals and some at ½-mile intervals as necessary. The Lodge project sensor spacing is generally less than 1 mile or a ½ mile in locations where detection is required.
The first major MDOT objective was to provide motorist information in the first stage closure that included 6½ miles between Eight Mile Road and the Davison Freeway (M-8) on Feb. 2, 2007. Nearly half the DMP were operable for this initial closure. The second staged closure, closing 3½ miles of M-10 between Lahser and Eight Mile Road, required all remaining equipment to be operable. This staged approach allowed MDOT to identify and correct any problems in advance of the remaining deployment schedule.
During the 2005 and 2006 projects, MDOT provided delay-time information using the RTWS. The 2007 Lodge Freeway project closed M-10, and there was need to display travel time in lieu of delay time along the two major freeway detour routes (I-75 and I-96). In addition, MDOT determined that delay time has a negative connotation to the information as compared with the more positive message of travel-time information. Motorists seem to respond better to the travel-time information. MDOT has deliberately kept the information simple and has designed the system to meet the specific needs of the metro region.
Initially, MDOT designed the RTWS to cater to two types of commuters: those traveling to the Telegraph Road (U.S. 24) areas and those driving all the way to downtown Detroit. The signs showed travel time to multiple destinations, and MDOT later realized that the message was a bit confusing. As an example: Travel time was posted from the northwest part of the region to U.S. 24, a major MDOT nonfreeway trunk line. Once motorists reached the U.S. 24 destination, the remaining DMP provided travel time from U.S. 24 to downtown Detroit. The multiple destinations proved to be confusing. The construction office revised all the static messages on the DMP to include the single-largest destination in the metro region: downtown Detroit. MDOT found that motorists traveling to destinations other than downtown Detroit can still utilize the travel-time information, regardless of their destination.
Driving through issues
MDOT continues to improve the design and management of the RTWS on each successive project deployment. Here are some highlights:
- Adequate temporary sensor quantities will increase the accuracy of the travel time. Typical density of 1- to a half-mile spacing is ideal. This will add cost and time to the RTWS but provides motorists the most accurate information. MDOT permanent sensors were inoperable on several occasions, and inaccurate information was being displayed. Misinforming the
- Use of gel-filled maintenance-free batteries because wet batteries (water-filled) created gases that caused malfunctions in the equipment;
- Early layout of the sensors, signs and cameras. This reduces deployment time and unnecessary adjustments to the system;
- Web-based access to monitor the system and revise messages is key to getting the greatest value out of the system; and
- Temporary cameras at strategic points of the project and along detour routes provide a great view of the system from the MDOT control room for incident management.
MDOT has received kudos from the FHWA and the motorists.
“The best engineering we can do is designing systems that work well with motorists,” said Dave Morena, safety and traffic operations engineer at FHWA.
Motorists are comforted when they know the travel times on the roadways and can make informed decisions. The information highway on the real highway of the future is RTWS.
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