It can be a bit unnerving to work on a job site with cars and trucks motoring by at fairly high speeds. Keeping your worksite visible is one way to stay safe. Another is to take advantage of "bump trucks," officially known as truck mounted attenuators. The nickname aptly describes what these devices do. They stand in the way between your crew and oncoming traffic and take the "bump" if a vehicle should wander into your site. The following includes some basic information on these life-saving devices, how they are used and the various types available.
The attenuator is actually the rectangular box that is attached to the truck. That steel box is filled with energy absorbing material that softens the blow for both the truck and the vehicle crashing into it. When attenuators were first being developed, some of the tests involved controlled crashes of cars into the devices to determine how the drivers fared.
The earlier models used sand, but test results gradually led to high-density foam filled devices of today. The inside works like an accordion bellows, with alternating layers of steel and foam. When the attenuator is hit, the bellows compress, just like those on an accordion when it's played.
Uses of Attenuators
Attenuators come in stationary and portable varieties. Both have specific uses.
Stationary attenuators are normally installed on the most dangerous areas on a roadway. For example, the gore point is a triangular zone that is found where lanes merge on or off the roadway. You'll also find them where the roadway leads to a bridge over-crossing and/or other situations where the number of lanes decreases or increases. The most common type of stationary attenuators are barrel-like containers that are installed in rows along the danger zones. They tend to be boldly coloured with black warning stripes and may be placed with or without additional signage.
The truck mounted portable versions are used to protect construction zones and to provide a safe zone for officials working an accident or other types of emergencies. The truck is parked in back of the work or accident zone. The idea is that if a vehicle loses control it will hit the attenuator rather than the workers or their equipment. The attenuator is accompanied by safety equipment that make it and the worksite more visible. This usually includes flashing arrow signs and/or a programmable message box to give drivers a heads up. Typical messages include "Traffic Delays Ahead" or "Road Work 1 Kilometre." The text must be easy to read at a glance.
Types of Portable Attenuators
Portable attenuators are available mounted on trailers or trucks.
Just like any other trailer, these attenuators hitch onto the back of a work truck. They fold up for transport, making them easier to tow. Once at the work site, the "bump box" folds down into place at the push of a button. One advantage is that you can unhook the trailer version and leave it in place while you use your vehicle for other tasks. Another is that you can share that attenuator between different vehicles.
These attenuators are permanently attached to the truck body. They tend to be larger and more visible than the trailer model, and a better choice for large construction sites along busy highways. The attenuators are designed to absorb the shock from a large vehicle crashing into it. The heavy duty truck and frame also help absorb the energy. Most truck mounted attenuators have built in electronic flashing arrows and/or signs that can be seen for kilometres because of the vehicle's higher profile.