Field Testing Showed That Sound Alarms from Work Zone Intrusion Alert Systems Should Be Distinctive and Long in Duration with a Level of at Least 110 dB When Located 50 Feet Away.

Oregon DOT research identified recommendations for deployment of work zone intrusion alert systems.

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The following recommendations were highlighted in the source document.


  • Based on the quantitative data collected and analyzed, the research team recommends that the sound alarm produced by the work zone intrusion alert technology should be at least 110 dB when the alarm is located 50 feet away from workers, and above 95 dB when the alarm is 100 feet away.
  • Types of sounds, such as a screeching noise or that emitted by an emergency vehicle siren, that differ from the noises heard during the operation (e.g., diesel engine noise from equipment, backup alarm on truck, passing cars) are preferred to improve sound distinction.
  • In addition, short-burst alarms should be avoided if possible. Alarms that provide longer, continuous sound improve the potential/possibility of capturing the workers’ attention.


Expected vehicle travel speed and time required for a worker to dodge the intrusion are key factors when determining the amount of adequate transmission distance. Given the distances between workers within the work zone and the need to provide adequate warning to as many workers as possible, the minimum transmission distance should be 400 feet when the work zone speed is 35 mph (85th percentile). This recommendation is based on the provision of a 6-second reaction time for a worker who is 100 feet behind (or in front of) the paving operation. The transmission distance requirement should increase for work zones with historically higher vehicle travel speed, higher maximum work zone speed limit, and greater expected distances between workers.


The study results indicate a consensus that the inclusion of a haptic feature with the alarm technology is beneficial to warn workers of an impending hazard. Providing haptic feedback to workers offers an additional type of warning thereby overcoming the issues related to a masked alarm sound due to heavy equipment noise or blocked line of sight resulting from vehicle movement. Based on haptic systems used in the communication industry, the researchers suggest a patterned vibratory signal that lasts for approximately 14 seconds and creates a vibration frequency of 150 Hz and 9.18 m/s2 acceleration.


Study results indicate that visual alarms tend to be an extremely important part of work zone intrusion alert technologies. Although no minimum “demand” luminance requirement for traffic control devices exists, the present study recommends the light produced by the intrusion alert should be visible 500 feet away.


Based on the evaluated impact of distances between the alarm unit and target operation on the response rate and reaction time of workers, it is recommended that the alarm unit be kept as close as possible to the crew members who are the most exposed to live traffic.


Study results indicate that ease of use plays an important role in the selection and implementation decision for work zone intrusion alert technologies. Workers prefer an intrusion alert technology that is easy to setup, deploy at the beginning of a shift, and retrieve at the end of a shift with limited exposure to traffic and need for workers.


The triggering mechanism of the intrusion alert technology plays a vital role in determining its effectiveness. The study found that most false positives are due to traffic cones with the sensing units being knocked over by mistake, wind, passing vehicles, etc. Therefore, radar or sensor-based work zone coverage that is independent of the roadway infrastructure or traffic control devices, or other non-impact dependent intrusion alert systems, are preferred choices for alert technologies in terms of the triggering mechanism.

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