• Overloading of Commercial Vehicles

     Our country has an extensive road network of about 5.90 million km. This road network is no doubt impressive in size, but unfortunately not able to provide the desired level of service and safety to road users. The unanticipated growth in volume of goods vehicles coupled with heavy axle loads carried by them, as compared to standard axle loads considered in pavement design, is responsible for causing extensive damage and premature deterioration of road network.

    The extra load carried on any axle of vehicle, more than that permitted legally by the Govt. is defined as over loading. As per Motor Vehicle Act, the Legal Axle load limit notified in July, 2018 is 11.5 tonne, 21 tonne and 27 tonne for Single, Tandem and Tridem Axles respectively. These values are amongst the highest when compared with developed countries. The truck operators resort to overloading for minimizing the total transportation cost per tonne km by carrying maximum pay load in least number of trips without bothering to the damages they are causing to the pavement structure.

    A more rational way of minimizing number of trips will be to use multi axle trucks with higher Gross Vehicle Weight (GVW) capacity, without overloading axles. Researches in the USA and South Africa have shown that an axle carrying double the legal load, may cause damage equivalent to 16 to 60 times that of a standard axle load (8.1 tonnes) depending on the conditions of the road structure.

    Overloading of commercial vehicles has been contributing to the premature failure of majority of road stretches in the country. The 10% and 30% overloading of vehicles reduces the pavement life by 35% and 65% respectively.

    The total load carried by each category of truck is much higher than the allowable limits. It is observed that in the category of two and three axle rigid body trucks, 30-40% vehicles are only within the specified axle load limits. The reverse is true in case of multi-axle trucks.

    In the axle load survey the trucks are randomly weighed for each axle, and in the loading of normal 2 axle truck, the front and rear axles carry load in the ratio 1:2. It is generally observed that trucks of all categories carry loads both in front as well as rear axle in excess of permitted limits. The overload front axle, even with lower GVW have severe damaging effect because it has single wheel tyre assembly.

    High percentage of trucks on our highways are overloaded and carrying maximum GVW of the order of 35 tonnes on 2 axle trucks and upto 65 tonnes on a 3 axle (rear tandem )trucks. It is learnt that 25 tonnes load is being carried on a rear axle of 2 axle truck, while upto 58 tonnes is carried on a rear axle in case of a 3 axle (rear tandem) truck. Even rear axle of a bus is found to carry a load of the order of 13 tonnes.

    Vehicle Damage Factor (VDF) due to overloading
    The input in design and maintenance of pavements is the stresses and strains developed in pavement caused by vehicle loads. Axle load data is analyzed to obtain the equivalent standard axles and consequently the weighted vehicle damage factor.

    Accepting the 4th power law of vehicle damage as valid, a gross vehicle weight of 25 tonne distributed over the two axles of a 2 axle truck (6 tonne on the front and 19 tonne on the rear axle) causes a VDF of 30 ESA while the same weight distributed on a tandem - axle truck causes a VDF only 3.19 ESA. Similarly, a gross weight of 48 tonnes distributed on 2 axle trucks results in a total VDF of 48.72 ESA. But the same load is distributed on three 2 axle trucks with in legal load limits, the VDF is 8.82 ESA and if the same load is distributed on two 3 axle trucks within legal load limits the VDF is 5.4 ESA.

    Pavement damage phenomenon due to overloading: The movement of commercial vehicles over the pavement causes the pavement surface to deflect to bowl shape resulting into development of stress and strains at different locations. Shape and depth of bowl depends on axle load of commercial vehicles. Stresses and strains are exponentially related to the axle load of vehicles and to the support of under lying layers.

    In the case of concrete pavements, the load is carried by beam action. The pavement deflects under the axle load of commercial vehicles, which is more in case of overloaded vehicles.

    Road pavement deteriorates mainly due to traffic clubbed with climatic and environmental reasons. But it is the vehicles, which are the major cause of road deterioration, especially on heavy trafficked roads. The passage of many vehicles, especially the commercial vehicles, has a cumulative effect, which gradually leads to cracking/ rutting of pavement due to fatigue. Overloading of commercial vehicles makes the design deficient leading to faster deterioration of pavements.

    Other related issues of overloading are higher vehicle operating cost, increased wear and tear of vehicles, air pollution and higher probability of fatal road accidents etc.

    The road are designed and maintained by highway engineers of public works departments, while the movement of traffic and checking of axle loads is with the transport department of State Govt. There is hardly any co-ordination between these separate bodies with the result overloading remains uncontrolled. As a result the vehicle damage factor is increasing over the years.

    Road accidents due to Overloading : Overloading is dangerous for the movement of vehicles and safety of road users because distribution of loads on axle plays an important role in higher rate of accidents. Due to overloading, the momentum of vehicles increases and on application of breaks, they overturn instead of stopping. Sometimes the over loaded vehicles at high speed while overtaking or at sharp curves, overturn and fell on other vehicles leading to accidents. Overloading puts the vehicle in an unbalanced state of axle load ratio to make it extremely unsafe for operation in the traffic stream jeopardizing the safety of all other road users. As per Road accident statistics published by MoRT&H, about 55,512 road accidents took place during 2017 involving overloaded vehicles in which 57600 persons got injured and 20848 persons were killed.

    The overloading of commercial vehicles is mainly for gaining advantage in the transportation cost for every tone km transported. The extra load carrying capability built in by the manufacturers of the trucks for safety is exploited by addition or extension in truck body carried out by transporters. 2 axle overloaded trucks are more damaging to the pavement in comparison to 3 axle and multi axle trucks. Both flexible and rigid pavements are designed with due consideration for axle load spectrum of the traffic operating on the road by converting axle load to equivalent axle loads but the excessive over loading of axles uses the design life much faster causing fatigue and deterioration of road leading to premature failure.

    Prevention of Overloading : To preserve our roads in a satisfactory service condition the most important single step is to enforce the legal load limits on vehicle in letter and spirit. As per the Motor Vehicle Act-1988, the penalty provision for Overloading is Rs 2000/ minimum and for every additional tonne of overloading Rs 1000/ per tonne extra. This is proposed to be revised to Rs 20000/ and Rs 2000/ per tonne for overloading in the draft Revised Motor Vehicle Act . There is also a proposal in revised MVA not to allow overloaded vehicles on roads. Movement of vehicles on roads allowed only after removal of excess load. Hope this will prove to be a major deterrent for overloading on our roads.

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