Use Bluetooth sensors to improve detection of traffic stoppages in work zones where other non-intrusive portable traffic speed sensors may only report average speeds.
Experiences from a CDOT implementation of Smart Work Zones.
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United States

Smart Work Zone (SWZ) Lessons Learned


In April 2013, the Colorado Department of Transportation (CDOT) activated a Smart Work Zone (SWZ) system as the first part of a long-awaited bore widening of the eastbound Twin Tunnels project on I-70 west of Denver. This project was the first of several highway improvements proposed along this corridor to address the heavy traffic congestion that occurs every weekend and holiday in the eastbound direction as motorists are coming home from their recreational trips in the mountains.

The Smart Work Zone (SWZ) system consisted of several devices linked together in a wireless network to perform as one unit. The components included portable non-intrusive traffic sensors, portable pan-tilt-zoom cameras, portable message sign panels (PMSPs), and software with user-defined parameters to collect and analyze data and trigger new messages on the system and/or send warnings to appropriate personnel. It also included a central control system for various data processing and communication functions, and a website for user interface and data display.

The main purpose of the SWZ system was to collect real time vehicle data at various locations, in advance of and within the work zone. The data would be used to inform the affected motorists a well as the Colorado Transportation Management Center (CTMC) personnel, the SWZ Project Engineer, and the Region 1 Traffic Engineer of operational conditions and historical data related to traffic delays, stopped conditions, queuing, and other pertinent traffic information. The ultimate goal was to assist the affected drivers in reacting accordingly and/or planning their travel through the work zone.

Lessons Learned

The Smart Work Zone project team learned many significant strategies that will be important for future Smart Work Zone projects for Colorado and elsewhere. Among others, they are as follows:

  • Be attentive to character limits on message display signs. Standard maximum number of character display per line on a typical PMSP is limited to eight (8) characters. This is important when figuring out the proper PMSP messages.
  • Understand traffic psychology and steer clear of ambiguous text on message display signs to prevent motorist misinterpretation. A few months in the project team had to change "9 MI TO" to "9 MLS TO" as the public was sometimes reading "MI" as minutes and getting confused.
  • Use "delay" messages with caution. "Delay" messages could have a negative public relations effect; project staff are sensitive to messages that could affect the public perception of their projects.
  • Adhere to policies about not displaying speeds above posted speed limits. Speed displays should not be the actual speeds exceeding speed limits. Speed sensors will always capture actual speeds within the detection zone.
  • Be prepared to blank out signs in case of activities that could occur outside the detection zone. For example, the nearby rockfall mitigation project was slowing traffic but those impacts were not within the detected zones, creating confusion (as mentioned in the report). It is best not to display messages pertaining to the work zone if there are other activities outside the detection zone that could affect the effectiveness of the traffic messages.
  • Check for sufficient bandwidth in mountainous areas. The challenge that was experienced during the initial stage of the project was related to available cellular signal in the mountains. It was learned that the best network provider had only two towers in the corridor that were receivable by the devices. The contractor had to install supplemental antennas and special programming to correct for frequent low bandwidth conditions.
  • Anticipate additional maintenance of the devices for cloudy and snowy conditions. Due to cloudy conditions and snow cover, the batteries were getting drained early and frequent battery charging using generators became necessary. It was learned that in the Idaho Springs area, the local weather phenomenon (year round) includes mostly cloudy conditions and mountain shading, resulting in added maintenance of the devices (such as battery charging).
  • Use Bluetooth sensors to improve detection of traffic stoppages in work zones where other non-intrusive portable traffic speed sensors may only report average speeds. Bluetooth data and messaging were added to website. It was decided to add two Bluetooth sensors on the project in order to have a more accurate measurement of travel time within the work zone. The speed sensors can also capture travel time. However, it is reported using only average speeds. Measurement of the typical "stoppage" of traffic does not work as well with speed sensors as it does with Bluetooth sensors.

Based on a study of the results of the 7-month I-70 Smart Work Zone project, CDOT Headquarters ultimately recommended that CDOT continue to deploy Smart Work Zones in future construction projects, with the following suggestions:

  • Empower the Region Traffic Unit/Operations Engineer to evaluate which locations are best suited for Smart WZ deployment based upon: project duration; space for devices; lane configuration; and available decision points (for dynamic routing).
  • Involve the CDOT Office of Public Information as early as possible to help explain the project to the general public.
  • Where possible, integrate the Smart Work Zone with permanent ITS devices.
  • Incorporate back of queue notification (especially where dynamic routing is unavailable).
  • Don’t message travel time or delay on a corridor that already has it.
  • Select two to three Smart Work Zone vendors via non-project specific contract (or other contracting method) with a price agreement versus a design-build RFP.

CDOT Headquarters also made recommendations on specifications for future Smart Work Zone projects:

  • Revise the specs to require that Bluetooth technology be used for the data collection.
  • Use the following lump sum items to eliminate daily documentation requirements associated with items paid for by the day: Smart WZ (sensors, cameras and software); and Reset Smart WZ Devices (VMS boards, cameras, and sensors).
  • Pay for VMSs as EACH vs DAY to realize a cost savings.
  • Add two 3rd-party weekend/holiday/event managers (one at project site and one at CTMC).

Smart Work Zone (SWZ) Lessons Learned

Smart Work Zone (SWZ) Lessons Learned
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Colorado Department of Transportation
Colorado Department of Transportation

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