Application Notes

Trigg Industries supplies complete systems, including detectors, warning signs, alarms, mounting poles and all needed accessories. We build to meet US and International AC power specifications, as well as Solar (DC) configurations.

Trigg Industries offers technical options to meet varying requirements and can provide cost effective solutions for virtually any overheight warning condition. Custom systems can be provided as needed.

men installing OHVDS system

TABLE 1: Site Selection Considerations

1. What is the posted and practiced speed limit at the installation site? Vehicle speed determines (in part) the distance from the detector the warning sign must be placed to provide sufficient time for drivers to react to directions given.
2. What exits, pull-offs or U-turns are available between the detector and obstruction? Availablity of such options must be taken into account as courses of actions for overheight vehicle drivers and directions given to them accordingly.
3. Will the detection system monitor one-way or two-way traffic across the roadway? Determines whether system must be direction discerning.
4. What are the number of lanes in the direction of interest? May further determine distance required between detection and warning sign/exit if lane changing is involved.
5. What is the height of the obstruction (clearance required) and is there the same clearance for each lane? The shape and/or contour of the obstruction or roadway may require more than one OVDS to monitor multiple heights or axis.
6. Are there any weather or airport radars within 1/4 mile of the OVDS installation site? Since both the Visible Red and Infrared detectors are made from silicone substrate, it may be possible to generate a false alarm if the detector is looking directly into the radar.
7. What will be the smallest sun angles encountered with respect to the detectors' site? The Visible Red detectors need a 3° clearance from direct sunlight and the Infrared detectors require an 8° clearance.
8. Is there 115 VAC power available on both sides of the road at the installation site? If AC power is not available, solar power may be an option. There can be a combination of both AC and solar power within the same system if necessary.
9. What is the desired alarm time? This is the cumulative time requirement considering speed, distance, number of lanes and required driver response. Our systems offer 1-30 sec, 5-60 sec as a standard feature and custom times up to 5 minutes at no additional charge.
10. Is remote reporting of an overheight detection and/or fault condition required? If so, this requirement dictates choice of system.
11. What are the local traffic patterns? These may influence directions given to drivers in overheight situations.
Trigg Industries welcomes the opportunity to discuss any overheight application.

Detection Concept

illustration of truck driving through OHVDS beam and warning sign

FIGURE 1: Detection Concept 

Overheight vehicle is detected by OHVDS.

Alarm Bell activates with Warning Sign. Parabolic shield focuses sound toward vehicle, drawing attention of driver to Warning Sign.

Warning Sign activates with Alarm Bell. Sign message alerts driver to overheight hazard and provides directions for appropriate response.

Typical Installations

• Bridges 

• Tunnels 

• Overpasses 

• Temporary Falsework 

• Railroad Tunnels 

• Airport passenger

dropoff overhangs and

pedestrian walkways 

OVDS warning diagram

FIGURE 2: Bridge, Tunnel, Overpass, Falswork Installation 

• Weigh Stations 

• Load Height

Verification for 

- Equipment Yards 

- Car Carriers 

OVDS warning diagram

FIGURE 3: Weigh Station and Load Height Verification Installation 

Metro Economy OHVDS installed inside parking structure detecting a single height.

OVDS single-beam detection diagram

FIGURE 4: Entrance Monitoring

Dual Single Eye OHVDS installed outside parking structure detecting two different heights.


•If vehicle is detectedby OHVDS #1, driver isinstructed by VMS topark where clearance isadequate.

•If vehicle is detectedby OHVDS #2, driver isinstructed by VMS to stopand wait further direction.

OVDS dual-beam detection diagram

FIGURE 5: Multi-level, Multi-height

If vehicle is overheight, the Variable Message Sign (VMS) displays a sequence of messages instructing driver where or where not to park. The gate can be delayed from opening while messages are displayed.


•Message 1: "STOP"

•Message 2: "TOO TALL"

•Message 3: "PARK LVL 1"

variable message warning sign (VMS) diagram

FIGURE 6: Gate Interface

Roadway Views

OHVDS transmitter and reciever optical beam diagram

FIGURE 7: Cross Section of Roadway

OHVDS transmitter and reciever tilt and grade diagram

FIGURE 8: View Across Roadway

Typical Pole Sway Limits

OHVDS transmitter and reciever setup diagram

FIGURE 18: Typical Pole Sway Limits