Police Sergeant Harri Huhtala from the Finnish mobile police has a revealing set of pictures in his folder.

A Saab 900 driving in front of the police car was towing a heavy timber load that had been loaded onto the rear part of the trailer. Suddenly the trailer began to skid and the driver could no longer control it. The car and the trailer ended up onto the other lane with the front pointing to the opposite direction. Luckily enough there were no other vehicles on the road at that time.

- If you put most of the load to the rear, it forces the towbar off the hook and lifts the car’s rear wheels up. It is impossible to control this kind of a combination at least if you have to dodge something, Mr. Huhtala says.

In the busiest holiday and building season in summer, vehicle and trailer combinations are a constant concern for the police, of course not to mention caravans, horse transport trailers, boat transport trailers and the like.

- People are not very well aware of how much different things in fact weigh in a trailer. Besides, hardly anyone teaches them how items should be loaded properly.

One cubic metre of sand, for instance, weighs 1600 kg so if the permitted weight limits are taken into consideration, a trailer can only hold a 25-centimetre sand layer.

- We have weighed some trailers with up to 2 500 kg loads even though their carrying capacity is only 650 kg. Tyres simply cannot hold that much weight and the towbar breaks down.

A scale would be useful in pick-up storage areas

According to law, the maximum load for a brakeless trailer is 750 kg and for a braked trailer 3 500 kg. Of course you have to deduct the trailer weight from this, keeping in mind that even a “light” trailer easily weights 150 kg.

- You can put a 500 kg load on this trailer. Overloading has sometimes been quite close, says Markku Pusenius, who is loading timber onto his trailer at a pick-up storage area in Tampere.

This time the load, which is going to Korkinmäki only some four kilometres away, is fully legal. There are only some planks in the trailer, though they must be partly loaded onto the towbar because of their 5-metre length.

- Pressure-impregnated timber and hard plaster boards are surprisingly heavy.

You can load much less impregnated timber onto a trailer than ordinary dry timber.

Markku Pusenius would not mind if there was a drive-on scale in the pick-up area just to make sure that the load is legal. Sales Manager Tommi Helenius, too, thinks that the scale could be useful.

- Our warehousing staff can advise the customer about proper loading, though in the end it is the customer who is responsible for the weight of the load. We can provide rope for fixing the load and warning signs for very long loads. We also sell straps.

According to Mr. Helenius, it is easy to check the weight of bagged items even in the pick-up area, but trying to assess the total weight of timber, iron or board products easily becomes guesswork.

The weight of a loaded brakeless trailer may not exceed a half of the towing vehicle’s weight. If the trailer has brakes, its total weight may not exceed the towing vehicle’s weight shown in the registration certificate – unless the manufacturer has set a smaller weight.

The load must be placed onto the trailer in such a way that most of the weight is on the towbar. If rear overhang is necessary, make sure that it does not cover the trailer’s lights and remember to attach a sign, red light or reflector to the rear overhang.

The front overhang may not exceed one metre and should be marked with a white flag.

A B-class license entitles you to drive a tandem vehicle whose weight does not exceed 3500 kg and has a braked trailer. You need an E-class driving license if the towing vehicle’s weight is smaller than the trailer’s total weight shown in the registration certificate and always if the tandem vehicle weighs over 3500 kg.

If the trailer is large, make sure that it does not obstruct mirror visibility. When standing behind a loaded trailer, you should be able to see at least a half of the side mirrors. If you cannot see the mirrors at all, you must place them on extension arms.

Make sure that the trailer tyres are in good condition, tyre pressure is correct and the trailer lights work. The police have noted that the tyres and structures of light trailers in particular are often in very poor condition.

- If the towing vehicle has studded tyres, they should also be mounted onto a braked trailer. Unstudded tyres can be used on a brakeless trailer throughout the year, says Harri Huhtala.

When loading items onto the trailer, they must be strapped down and supported properly to make sure that they do not fall during the ride. Note that the driver is always responsible for possible damage caused by items falling onto the road.

The most reliable way to ensure that the load stays on the trailer is to use proper fabric straps, which can be tightened with a lock mechanism even during the ride.

6-10 day fines are typically prescribed for overload. If the load is considered to endanger traffic safety, the fine may even higher.

- Trailer weight and behaviour should be taken into consideration when stopping and in corners, Mr. Huhtala points out.

Kari Pitkänen

- The maximum weight of a brakeless trailer is 750 kg and that of braked trailer 3500 kg. The manufacturer may set a smaller permitted trailer weight for the towing vehicle.

- The trailer weight limits are indicated in the vehicle registration certificate. The permitted maximum weight also includes the trailer’s empty weight (150-250 kg).

- The highest permitted trailer width with load is 2.6 metres.

- Braked trailers must be technically inspected every other year.

- The highest permitted driving speed with a trailer is 80 km/h or any lower speed assigned by a traffic sign.

Some material weights per cubic metre: