Tractor jackknife warning

Because tractor drawn aerials have the capability to jackknife there are warning systems for both the driver and tiller operator to alert them that they are approaching a jackknife position. When the system senses that the tractor and trailer are at a preset angle to each other the alarm will activate. The warning system signals the driver and tiller operator with both an audible and visual alarm.


The jackknife visual alarm is a light that is located in the cab and will illuminate when the alarm is triggered. It’s very important that the driver is alerted to the potential that the apparatus is approaching the jackknife position; therefore it is imperative that the light is located where the driver can clearly see it. When driving in tight, diminished clearance situations, the driver will be heavily concentrating on their surroundings and may not be aware that the apparatus is close to the jackknife position. If the light is not easily viewable and the driver is focused on the circumstances around them, they may not see that the light has activated.

During the design, careful consideration should be made to centrally locate this light on the dashboard in an open area. The two below pictures are good examples demonstrating how the jackknife lights are clearly visible for the driver as they operate the tractor. (Click to enlarge)


Non-desirable light locations


example 1:

Here the jackknife warning light is located at the base of the steering column, making it virtually impossible for the driver to see it when it is activated. Based off the available space or lack of space on the dashboard, this light can easily be misplaced during the design phase. (Click to enlarge)

example 2:

In this example the jackknife warning light was positioned at the top of the dash. With the steering wheel in its normal position, the warning light is fully blocked by the top of the steering wheel. It’s only after you lean forward and peek over the steering wheel that you’re able to see the light. Because the warning light is such an important component to the jackknife warning system, attention must be taken to not allow the light to be obstructed. (Click to enlarge)

Example 3:

This jackknife warning light is placed on the dash above the drivers head. Although the light is not obstructed by any obstacle, its location is higher than the driver’s normal line of sight. If the driver is completely engaged in maneuvering the tractor, they would have to look up to see that the light has been activated. (Click to enlarge)


The brightness of the jackknife warning light is just as important as its location. It’s essential that the light illuminates bright enough to get the attention of the driver when it is activated. Again, if the apparatus is getting close to the jackknife position the driver will generally be deeply absorbed in maneuvering the tractor and may not have the capacity to observe the light. 


In my department, we specify that the jackknife warning light is a blue LED positioned on the upper right-hand side of the dash. Although the light is small in dimension its intensity far surpasses its size. Because most warning lights are red we specifically require this light to be blue which distinguishes it from the rest. (Click to enlarge)

audible alarms

The jackknife audible alarm is just one of many audible alarms on a tractor drawn aerial. Actions that will produce an audible alarm are things like compartment open, apparatus doors open, seatbelt alarm, buzzer system for driver and tiller operator, and tiller operator not seated. It is essential during the design phase to specify that the jackknife audible alarm remain a separate sound than the rest of the warning alarms.