Highway authorities around the world stipulate weight restrictions of road-going vehicles mainly to minimize the high costs of road reconstruction, repair and maintenance. They want to make sure that road surfaces survive as long as possible.
There are road safety issues relating to vehicle weight too. A vehicle that is too heavily loaded may not have a safe braking distance. But that is primarily an issue for vehicle manufacturers. They should stipulate how great a load is safe to pile onto the vehicle without compromising safe driving and stopping.
In Canada and certain US states, highway authorities require that large mobile cranes have to be swung round to the back and supported at the rear by a boom dolley that is hauled by the crane as a trailer. The advantage of a boom dolley is that it reduces the loading on the crane’s axles by taking some of the weight of the boom off them. This, therefore, creates less road damage. But trailing a boom dolley increases the turning circle radius of the vehicle, which makes it less safe. According to Canadian crane users, a trailing boom dolley increases the length of a Liebherr LTM 1080, for example, from 12.6m to 23m. Because of this hazard, trailing boom dollies are banned in Europe, although fixed tag axles are sometimes used to reduce the ‘per-axle’ weight.
In the Canadian province of Alberta, a group of crane users concerned about the safety of trailing boom dolleys has organized to challenge the regulations there, and is seeking to persuade the provincial government that modern all terrain cranes do not cause the kind of road damage that the authorities seem to think they do.
Terry Danderfer, president of Canada Crane Services of Nisku, Alberta, explains: ‘I originally started talking to Alberta Transportation approximately 10 years ago about the issue of cranes pulling boom dollies. I have never thought it was a good idea, but they of course responded with, “show us the science and we will consider it”’.
An action committee was formed by Alberta’s prominent mobile crane owners, with Danderfer himself, Bob Van Englen of Northern Crane, John Storms of Mammoet, Jim Sandmaier of Sterling Crane and Don Provencal of the oil company Syncrude Canada. The action committee is chaired by Don Mosicki, a councillor at Leduc County, supported by Leduc County clerk Brian Bowles.
Syncrude’s involvement is significant. It is not just a major crane owner but also the dominant client of the other companies represented. It also has a global reputation for taking crane safety to its limits. It has also had two incidents of the boom slipping out of the saddle, resulting in blockage to public roads, says Don Provencal, who area supervisor of Syncrude’s central equipment services division. It has also had eight ‘near misses’, one of which could have been catastrophic – a swinging hook almost wiped out a school bus.
The aim of the action committee was to fund and commission research that would give Alberta Transportation the science it had asked for. After the Crane Rental Association of Canada’s annual conference, the group acquired C$400,000 in funding – $139,000 from Syncrude. The official name of the study is the Alberta Road Research Initiative, or ARRI. The technical committee includes engineers and materials scientist from the University of Calgary, Alberta Transportation, Leduc County and Syncrude.
Says Danderfer: ‘We have formed a technical committee to design and implement a test track to study the impacts of all terrain suspension as well as various tyre pressures on pavement, cold mix and gravel. The track will be unique in that we can gather data for all three road types through seasonal temperatures from minus 40 degC to plus 30 degC.’ The impact of all terrain cranes on the different pavement types will be tested over the course of several seasons.
‘Our ultimate goal is to have a national standard for all cranes which would see the cranes pulling trailers only in special circumstances, such as crossing of structures or on banned roads.’
Comments or information can be emailed to the ARRI project at cancrane@telusplanet.net
