Be Safe on the Road! Know the Load!
As farmers struggle to complete harvest, there is pressure to quickly get the crop safely out of the field and into storage. However the crop won't matter much if your harvest practices mean you or someone else does not make it home! Nothing hurts a farm business more than a serious injury or worse yet, a fatality.
Let's start with the picture below. Four gravity wagons strung together to be filled and towed down the road to the farm. Maybe these empty wagons were brought to the field as a single unit but will be disconnected so that only one or possibly two full wagons are connected for the ride home. But, there are lots of cases where farmers take these risky chances and try and pull this entire load home.
Figure 1. Really! What's wrong with this picture? Seen on the back roads of Ontario, Thanksgiving Monday 2018.
Have you thought about what is involved here? Let's do the math using soybeans (because I can't do the darn math with wet corn):
- 4 gravity wagons and running gear - ~3000 lbs each empty = 12,000 lbs
- 400 bu per wagon @ 16% moisture and 60lbs/bu - 24,000 lbs each = 96,000lbs
- Total towed weight: 12,000 + 96,000 = 108,000 lbs (49 tonnes)
One single 1" diameter (or maybe 1-1/8" if we're lucky) draw pin at the tractor carrying all the weight behind it with 3 more draw pins (one on each wagon) carrying progressively lower loads. How strong is that pin? Just like bolts, hitch pins have grades. A 1" diameter grade 5 pin will shear under a load of 38,500 lbs - meaning if you were to hang 38,500 lbs from the pin, it would break. When towing, you aren't carrying the entire weight on the pin, but it's still a good gauge for the load limit. Consider the added stress on the pins when you jerk the load on start-up or jam on the brakes in an emergency. AT MINIMUM, for this load, a 1.5-inch, grade 8 pin should be used at the tractor (shear strength of 122,000 lbs) if it will even fit the running gear of these 400 bu wagons. And that is for certified graded pins! A home-built pin? Don't even think about it!
The stress on that pin at the tractor depends on the weight of the load, the speed of transport, the stress of the braking force applied, and the amount of contact of the pin to the tongue and drawbar. The wagon hooked to the tractor has the weight distributed over two thin (the tongue hitch) and one thick (the tractor drawbar) contact points. The wagons behind have 3 thin contact points, two on the tongue of the following wagon, and a hitch plate on the forward wagon. Yes, they tow less weight but the thin steel of the towed trailers hitch plate has greater chance of breaking or twisting under load.
What about safety chains? The chain at the tractor must be of a grade/capacity to carry the entire load. The chains put on wagons by the manufacturer are rated for the capacity of a single wagon (maybe two wagons if you're lucky). Have you upgraded your chains so that each wagon in the train has a chain sized for the capacity of that wagon and the wagons attached to it? Likely not! But we shouldn't have to ask this question because no one in their right mind should be thinking of pulling such a load, RIGHT?
If the hitch or pin breaks on any one of the wagons, will that loose wagon(s) follow straight being towed by only the chain, or is it going to jackknife?
The vast majority of wagons do not have brakes. Bigger wagons may be equipped with surge brakes. But you have no control with surge brakes until the weight comes forward during braking. You have no way to engage the wagon brakes to start braking the load to correct potential jackknifing or start to stop the entire load. There is a high potential that the wagons will jackknife as they all surge forward during panic braking. Think also about not having enough tractor power to pull the load. If you run out of power for this load going uphill and stall, it is highly unlikely that the tractor brakes will be able to hold the load. The whole thing will slide backwards and jackknife with potentially devastating consequences.
Wagon manufacturers have commented that the only brakes they support are the hydraulic brakes hooked to the tractor system, or even better those hooked to a receptacle in newer tractors that connect the wagon brakes to the tractor brake pedals, enabling them to be set to engage when the operator initiates braking. Many people opt against the brakes because of cost on the assumption that their big tractor can control the load. THINK AGAIN!
What is a safe towing speed? If you come to the field empty at full road speed, is that the same speed you should be pulling a full load at? Obviously not, but what is your practice? Consult your equipment's Owner's Manual for information on safe travel speeds and weight limits.
Owner's manuals also include safe towing limits for tractors and other power units. In general, the towed implement weight should not exceed 1.5x the weight of the tractor. For the example above and using a 200hp tractor to pull that load, if the tractor weighs around 26,000 lbs its maximum towed weight should not exceed 39,000 lbs. That means this load would be almost 3x its suggested towed weight limit.
The tire choice and inflation pressure can also impact load dynamics under speed. Again, consult your Owner's Manual or a professional on what is safe for the load and configuration.
When we asked some equipment people what would be needed in a tractor to stop this load under emergency conditions, they all essentially said nothing would do, because the wagons would more than likely jackknife and the results would be catastrophic. They said they would refuse to connect to this load with any tractor.
Figure 2. What can happen when you don't think about safety in your daily farming practices.
Another common site during the season is the Slow Moving Vehicle sign (SMV). The purpose of a SMV sign is to make the public realize there is a slow moving vehicle ahead. It is important to consider slow moving vehicle signs in the psychology of their use. The purpose of the sign is to get people to associate seeing them with a vehicle moving slower than normal traffic on the road ahead of them. By using SMV signs on gates, camping trailers, driveways and other uses, the public can be desensitized to what they are facing. Add in the fact that they are often approaching at approximately 100 km/hr while the farm equipment is travelling 40 km/hr, and it's important that the awareness is instantaneous. Give them and yourself that awareness and reaction time by displaying and using SMV signs correctly!
Figure 3. The purpose of SMV signs is to make the public realize there is a slow moving vehicle ahead, not to mark the gate or lane entrance.
We need to build more thoughts of safety into our farming routines. We get complacent because it hasn't happened to us and think that it likely never will. Talk to someone who has experienced a tragedy and you will find that they once felt the same way. Replacing a faded slow moving sign, replacing a broken light, or taking the time for two safe trips instead of one seems like a small preventative action compared to the potential consequences.
Thinking and acting safely should be routine and instinctive. It takes "muscle memory" to make actions and thinking instinctive. Think, train and act safely for yourself and those around you. The goal should always be that you and those you come in contact with each day (including the people in the cars that pass you on the road), get home safely that night to enjoy their lives and their families.
For more information:
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|Author:||Ian McDonald with contributions from Jacqui Empson-Laporte, James Dyck, Alex Barrie and Terrance Sauve/OMAFRA|
|Creation Date:||01 November 2018|
|Last Reviewed:||01 November 2018|