There are two reasons why a bus may skid on the roads, firstly due to high speed and secondly, when the friction between the tire and the road has been reduced due to oil leakages from other vehicles, natural weather conditions like snow or due to wear and tear of the tires. Lets discuss every possibility separately;
Skidding due to high speed:
Buses are of 3 types, mini, midi and coaches. The minibuses seat up to 15 passengers, midi has 16 to 29 seats and coaches can comfortably seat up to 60 people. Irrespective of their size, every bus weighs more than a tonne i.e. more than 1000 kgs or 2200 lbs. For example the average weight of a minibus can be between 3 to 5 tonnes, depending of the number of features and equipment in the vehicle. Midi and coaches will obviously weigh more due to their larger size. Moreover, 15 passengers can easily add another ton of weight to the bus with their luggage included. The total weight of a fully occupied minibus can go up to 6 tonnes.
Lets, re-imagine the bus as a rectangular box that weighs approximately 6 tonnes. If this box had 4 tires and was speeding down the highway, then its weight would start gathering momentum due to the gravitational pull of the earth. To understand this concept, you need to understand the difference between potential energy and kinetic energy. When a bus is stationary, it has the potential to move forward even when its not moving forward, this is called as potential energy. When the engine is turned on and the bus physically starts moving forward, then its potential energy is converted into kinetic energy. As the speed increases, its kinetic energy increases too.
This is the mathematical formula to calculate the kinetic energy of a moving bus.
Kinetic Energy = 1/2 x M x V x V
where, M = mass or weight
V = speed of velocity
So when this huge rectangular box of 6 tonnes, starts moving on the road at high speeds, its kinetic energy keeps increasing. An increase in the value of V(speed or velocity) automatically increases the overall kinetic energy of the vehicle. Its impossible to stop such a huge load of mass with tremendous kinetic energy almost immediately. Because as the box gathers speed, its entire body weight gathers momentum in the forward direction. As the speed keeps increasing, the rectangular box acquires more and more kinetic energy and becomes a force that is moving in the forward direction. This force is pushing the entire bus, its passengers, equipment and luggage in the forward direction. Everything and everybody inside the bus is being pushed in the forward direction by this force. Anything smaller in size and lighter in weight that blocks the forward path of this force will get crushed and go straight under the bus. So when you apply brakes suddenly, even when the tires have stopped rolling, the bus will continue to move in the forward direction until its acquired energies have been exhausted and the pushing force has disappeared. When the energy(kinetic) is reduce to zero, the forward pushing force will automatically be reduced to zero. Its important to make the kinetic energy zero to halt the bus. From the above formula we know that kinetic energy is the product of mass and velocity. In simpler terms a product of weight and speed. The weight cannot be reduced to zero, hence the speed should be reduced to zero to halt the bus, which can be achieved by applying brakes and turning off the engine.
Now we come to the answer of the question. The V also called as speed has to be reduced to zero the kinetic energy of the bus. When this happens the bus will halt. But there is no way to reduce the speed from 80 miles per hour to zero almost instantly. When the brakes are applied the speed will gradually decrease from 80 to 70 then 60, 50, 40, 25, 12, 5 miles per hour and then finally to zero. So even when the tires have stopped rolling, it is the speed that is taking time to come down to zero. Speed has a natural tendency to come down gradually, not instantly. When the speed is reduce to zero its kinetic energy will become zero too and the forward pushing force will disappear, thus stopping the bus. For example, when the bus is operating at a top speed of 80 miles per hour, its kinetic energy according to the above formula will be approximately 19,200 Kilo Joules(KJ). As the speed reduces gradually from 80 miles per hour towards 0, its kinetic energy or acquired energy too reduces from 19,200 KJ towards 0.
The time taken by speed to gradually reduce to 0, determines the time its kinetic energies will take to get exhausted. They in turn determine how long the forward pushing force will take to completely disappear. So if the speed takes 4 seconds to be reduced to 0 from 80. Then the kinetic energy will also take 4 seconds to be reduced to 0. And the forward pushing force too will take 4 seconds to completely disappear. Thus, when the brakes are applied, the bus will continue to skid forward for 4 seconds until its speed and energy is 0.
The above figures are for explanation purposes only, in reality they can vary drastically. Bus drivers are trained to drive the vehicle within safe limits so that they can be stopped instantly. When the bus is riding at speeds within safety limits, it stops almost instantly but they skid only when the safe speed limits have been breached and increased.
Skidding due to spilled oil and natural weather conditions:
Bus tires are designed in a way that they stick to the roads. Friction causes the tires to stick to the roads. When the amount of friction is lowered than the normal amount, the bus starts to skid. This can be due to foreign substances coming between the tire and the road. Some of the most common substances that reduces this friction is oil spilled by other vehicles, snow, dust, mud etc. The driver should be careful and reduce the vehicles speed to make sure it does not skid. Because skidding can cause accidents and be injurious to passengers on board as well as pedestrians and other road users.
Worn out Tires and hydroplaning:
People may think water is not harmful to vehicle drivers. This may be true to a certain extent but if the tires are worn out then even water becomes dangerous for the vehicle. So, what are worn out tires? Tires are specially designed to have gaps or channels on them. These gaps are called as treads which tend to wear out over a period of time. The primary purpose of these treads to help the tire maintain a firm grip on the road. They even push water way thus maintaining constant contact with the road. When these treads get worn out, they are not able to push water away and let it come between the tire and the road, this phenomenon is called as hydroplaning and can be dangerous to safety of the vehicle. Chances are high the bus might start skidding in this case because of the lowered friction with the road. Bus and other vehicle owners are advised to check their tires every month to make sure they are safe for driving. Almost 26% of vehicle accidents in the USA are attributed to smooth and worn out tires.
Many people buy used buses for sale to meet their personal and organization group transportation requirements. They prefer second hand buses over their newer counter parts because they are affordable to purchase. The used bus market has been growing by leaps and bounds in the USA recently. But, people should remember that used buses have been on the road for up to a decade. These vehicles have already gone through a lot of wear and tear and so have their tires. Failure in this part of the bus can potentially cause loss of life and injury to people on board and those on the road. Buyers should always opt to purchase fully reconditioned used buses for sale rather than those that are being sold as is by one time sellers. This ensures the bus is in top condition and ready to hit the road once again. Purchasers dont have to go through the tedious task of fixing a bus after the transaction is complete. With reconditioned used buses, they can start driving immediate once the vehicle has been delivered to their site. Moreover, if they buy a 15 seater bus for sale then they can use it with a regular license because commercial license is not required to operate a small bus.
If you are searching for a bus to solve your group transportation needs, and dont know where to get started, then contact Major Vehicle Exchange by visiting our website. We have more than 45 reconditioned used buses for sale in stock ready for delivery across the USA. Choose the vehicles that have been listed on our website and give us a call during normal business hours and we will surely assist you not only in buying the bus but throughout the ownership process. We have been in business for 35 years due to the thousands of happy and satisfied customers customers across the United States. Our customers always come back for more and repeat sales plays a very important role in the overall success of our enterprise. Contact us today and we will do our best to get a used bus for sale that fits your needs 100%.
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