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Transport. Buses destroy the road surface 20 thousand. times more than passenger cars? We explain

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“Warsaw! The passage of one bus destroys the road surface more than 20,000 passenger cars!” – convinces the inscription on the illustration of the Warsaw branch of the New Hope party. Experts explain that although this sentence is formally true, it should be supplemented with the missing context.

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The Warsaw district of the New Hope party wrote on January 10 on Twitter and Facebook about “one of the many advantages of individual car transport” and published an illustration with the inscription: “Warsaw! The passage of one bus damages the road surface more than 20,000 passenger cars! Each bus passenger burdens the road more than 200 drivers. Be aware travelers.” The Twitter post alone has nearly 560,000 views and over 550 likes.

An entry from the Warsaw branch of the New Hope party (former Korwin) regarding the alleged advantage of individual transport over public transport.Twitter

Under the tweet of the Warsaw branch of New Hope, Internet users left over 300 comments. Many of them were critical or written in an ironic tone. “Hey listen, even if it’s true, let’s make separate lanes for buses so that they don’t spoil the road surface for cars, that’s brilliant, isn’t it? What do you think?”; “I must say that this is an extremely strong argument for bicycles” – wrote Internet users (original spelling of posts). Some commentators suggested that the illustration contained false data. Some asked for a source. “I have a friend who travels by collective transport (collective transport – ed.), but he does not support all these buses and says that it is true” – Jakub Wiech, deputy editor-in-chief of the Energetyka24.com website, ironically commented.

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The profile’s administrators – on Twitter and Facebook – fiercely defended their post against criticism. They referred to the Facebook comment of Janusz Górski, who introduces himself as “the perpetrator of all the fuss”. “To compare the impact of two vehicles on road wear, the formula for ‘aggressiveness of the axle’ is used” – writes Górski and compares the pressure of a bus weighing ten tons together with passengers with the pressure of a passenger car with a driver. The formula he uses shows that the pressure of the bus is exactly 20,736 times greater. Górski refers to the scientific studies of Dr. Eng. Dawid Rysia from the Gdańsk University of Technology and prof. Leszek Rafalski from the Road and Bridge Research Institute.

However, is the argument about the load of vehicle axles on the road surface justified in the discussion about the choice between city buses and cars? We asked experts how it is estimated how much different weights of cars damage the road surface, and when and why such calculations are made.

Heavy cars damage roads more than passenger cars? Dr. Ryś: This is not a special revelation

In a short study quoted by the Internet user published on the website of the Institute of Civil Affairs prof. Leszek Rafalski explains that the issue of the impact of vehicles on road surfaces was dealt with by French researchers in the 1980s and 1990s. “Based on tests on experimental tracks, they established a relationship regarding the impact of the vehicle on the road surface called ‘aggressiveness of the axle'” – explains Prof. Rafalski and explains how to use the formula to calculate it. “Currently, it is assumed that in the case of asphalt pavements, 1 truck with 2 axles loaded with 10 tons each corresponds to 3,200,000 passenger vehicles loaded with 0.5 tons per axle” – writes the expert.

We ask PhD Eng. Dawid Rysia from the Department of Transport Engineering at the Gdańsk University of Technology.

Yes, that’s roughly true. Which does not change the fact that collective transport is a much better solution for the environment than individual transport, and roads will deteriorate due to climatic factors, even if there is no traffic on them.

Doctor Ryś further explains that there are several different methods for determining the impact of vehicles on the road surface, which differ in how accurate the input data we have and how precise the result we want to achieve. The simplest, most general and most popular method is the fourth power formula. The formula allows to calculate how many axles with a given load Qj must pass in order to cause the same pavement damaging effect as the passage of a standard axle Qs. “According to the formula, the destructive effect of the vehicle axle increases to the fourth power. In other words, if the axle load of the vehicle doubles, the destructive effect will increase 2^4=16 times” – explained Dr. Ryś. “With several times greater loads on the axles of buses or trucks, the destructive effect caused by the passage will be tens of thousands times greater than the effect of the passage of a passenger car. This dependence, although it seems surprising to recipients who have nothing to do with road engineering, has been known since at least the 1960s of the 20th century and is not a special revelation” – sums up Dr. Eng. Lynx.

Prof. dr hab. Eng. Stanisław Gaca, director of the Institute of Road, Railway and Transport Engineering at the Faculty of Civil Engineering of the Cracow University of Technology explains that such research and analyzes concern the so-called fatigue life, i.e. the effect of reducing the mechanical properties after repeated loading and unloading of the pavement. He gives an example of a steel or copper rod, which, repeatedly bent and straightened, eventually breaks, even though we put a relatively small force on it. “Similarly, in the cyclical loading of the road surface by the passage of subsequent vehicles, the surface bends and returns to its original form, i.e. ‘pavement fatigue'” – explains Prof. Gaca. He goes on to explain that if the load is small or very light, there is no or very little deflection of the pavement, but in the case of trucks, it can be significant. But it takes hundreds of thousands or millions of vehicles to destroy the pavement.

Prof. Gaca: the structure of the surface must be adapted to trucks

We also showed Professor Gacy the entry of A New Hope with an illustration. “The information is formally true, but at the same time incorrectly presented and interpreted – the important context of the research on the so-called aggressiveness of the axis and the way the research results are used in practice” – the expert assesses in the analysis sent to us and encourages a realistic approach that takes into account how how and why roads are built. Usually, you need roads that allow trucks to move on them. “Even if the number of trucks was very low, the road surface must have the appropriate thickness for the load-bearing capacity” – he estimates.

It doesn’t matter if driving one truck causes the same “fatigue effect” as driving, for example, 10 or 20 thousand. cars, because the surface structure must be adapted to trucks anyway, and besides, in practice, e.g. the surfaces of major rural roads are designed for the passage of several million trucks in the planned period of use

Professor Gaca further estimates that such a surface, with very little truck traffic, would be destroyed by passenger cars, provided that 30-60 billion such vehicles pass. With a properly made pavement structure, the number of passing passenger cars is therefore not of great importance due to the effect of the fatigue life of this pavement. “Taking into account the information provided above, I do not really understand what the author meant when he wrote that we should consciously use the roads, because the passage of one truck/bus destroys the road in the same way as the passage of thousands of passenger cars, because in practice there is no need to considerations about which is better” – sums up the expert.

Dr. Ryś: A real problem? Overloading trucks

“The problem worthy of attention is not the fact that buses have a greater destructive effect on road surfaces than passenger cars, but the real problem is the phenomenon of overloading trucks” – says Dr. Eng. Dawid Ryś in the analysis sent to us. Polish and European law define the permissible vehicle load limits, as well as the permissible speed limits.

As can be seen from the formula of the fourth power, the increase in axle loads causes a drastic increase in pavement wear. And studies show that between 15 and 25 percent. trucks are overloaded.

Dr. Ryś estimates that on some roads for which there is no data, this percentage may be higher. “We have calculated that trucks cause up to 70% of damage to the surface. The durability of the surface is shortened, the condition of the surface deteriorates, which, as drivers, we feel as unevenness. In addition, it is very costly for society because we have to spend more money on repairs and maintenance” – he notes expert.

Dr Ryś notes that there is an understanding in society that exceeding the speed limit on the roads translates into reduced road safety. However, in the case of exceeding the vehicle loads, awareness is negligible, and the control of loads by the relevant services is not so effective. “We all contribute to the journey of each overloaded car as taxpayers, and the dishonest carrier benefits” – concludes Dr. Ryś.

Author:Krzysztof Jablonowski

Main photo source: Shutterstock/Twitter





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