Data acquisition was based on a questionnaire addressed to 16 individual Provincial Marshal Offices in Poland and included owner observations. Based on the annual data for 2008 to 2018, including the total sum and quantities of generated, collected and recovered tyres, an analysis was conducted that includes the determination of the mass accumulation indicator of tyres by area (division by country and voivodeship in Mg km− 2). The waste accumulation indicator by area was used in studies by Przydatek and Ciągło (2020) and Xiao et al. (2012). Generated waste tyres are primarily produced in vulcanisation plants, service points, and vehicle and dismantling stations for end-of-life vehicles (NWMP 2016).
According to Miliute-Plepiene and Plepys (2015), the number of studies considering waste accumulation indicators is increasing, which may result from the need to identify factors causing an increase in the mass of generated waste. In addition, based on Statistics Poland (2008–2018), the number of registered vehicles in Poland was determined. This number included motor vehicles, buses, lorries, special cars, tractor units, agricultural tractors, motorcycles, and mopeds.
A statistical analysis was also performed that included the maximum, minimum, and average. To determine the correlation relationship meeting the condition of the normal distribution for the data covering the total number of tyres, including those generated, collected, and recovered, the Pearson linear correlation coefficient method was used. When the condition of normal distribution was not met, Spearman’s rank method was applied. The Spearman correlation coefficient R is a non-parametric equivalent of Pearson’s coefficient. As with parametric correlation, the Spearman correlation coefficient R measures the strength of the correlation between variables. Non-parametric tests were used due to the lack of normality of the distribution of most of the analysed indicators following the results of the Shapiro-Wilk test (p < 0.05) (Przydatek and Kanownik 2019).
The non-parametric Mann-Kendall statistical test was chosen to test a series of numbers in terms of identifying an upward or downward trend that is not necessarily linear. Statistica 13 (StatSoft Poland, StatSoft, Inc., USA) was used for statistical analysis.
Used Tyre Quantity Analysis
The total volume of used tyres collected in Poland from 2008 to 2018, broken down by the 16 individual voivodeships, is listed in Table 1. The smallest mass of collected tyres was recorded in the north-eastern part of the country, specifically in the Podlaskie Voivodeship, whereas the highest was in the central-western region of Poland (Greater Poland Voivodeship, area 35.66 Mg km− 2). These values were respectively 42,067 Mg and 1,063,657 Mg. In contrast, the highest indicator of accumulation of used tyres at 48.06 Mg km− 2 occurred in the southern part of central Poland (Świętokrzyskie Voivodeship, 15th in terms of size in the country − 562,848 Mg, whereas the lowest was 1.94 Mg km− 2 in the north-eastern part of the country (Warmian-Masurian Voivodeship fourth position − 46,983 Mg) (Table 1). The total amount of tyres during the 11 analysed years ranged from 708.24 to 135,570 Mg with an average of 32,741 Mg (Table 2).
Table 1
Total amount of used tires divided into administration regions of Poland
Voivodeship | Amount of tires | Tire’s accumulation |
Mg | Mg km− 2 |
Lower Silesia | 116,813 | 5.86 |
Kuyavian-Pomeranian | 175,155 | 9.75 |
Lublin | 427,502 | 17.02 |
Lubusz | 595,164 | 42.55 |
Łódz | 327,739 | 17.99 |
Lesser Poland | 348,935 | 22.98 |
Mazovian | 234,703 | 6.60 |
Opole | 446,564 | 47.45 |
Podkarpackie | 548,455 | 30.73 |
Podlaskie | 42,067 | 2.08 |
Pomeranian | 109,527 | 5.98 |
Silesian | 209,118 | 16.96 |
Świętokrzyskie | 562,848 | 48.06 |
Warmian-Masurian | 46,983 | 1.94 |
Greater Poland | 1,063,657 | 35.66 |
West Pomeranian | 159,434 | 6.96 |
Min | 42,067 | 1.94 |
Max | 1,063,657 | 48.06 |
Average | 338,416 | 19.91 |
Table 2
Average amount of generated, collected and recovered used tires in Poland
Indicator | | | |
Mg |
| 32,741 | 708.24 | 135,570 |
| 14,295 | 73.16 | 80,197 |
| 16,060 | 0.50 | 58,401 |
| 3,950 | 467.02 | 38,134 |
pcs. |
Vehicles** | 52,471,172 | 43,389,232 | 62,570,032 |
*on the base data from voivodships |
** on the base data Statistics Poland |
In the analysed years, the accumulation indicator of collected tyres per unit area in the country ranged between 0.93 and 2.12 Mg·km− 2 (Fig. 2). During this period, the lowest total amount of waste tyres was 292,277, but the highest was 663,935 (Fig. 3a). Moreover, the number of vehicles registered ranged from 43,389,232 to 62,570,032, which increased by as much as 19,180,800 (Fig. 3b). The highest number of vehicles (284,065,550) comprised motor vehicles and tractors (49.22%), but the lowest number (1,152,220) was for buses (0.20%). The extreme values for the accumulation rate and number of used tyres were recorded in 2009 and 2017 (Statistics Poland 2008–2018.
The variability of the indicated data was presented in Fig. 4, with recovered tyres at 47% and generated used tyres at the lowest share (11%; Fig. 5). However, the maximum values differ significantly in this respect. The highest value of 80,197 Mg occurred for collected tyres, excluding the total amount of tyres.
The average values of the collected and recovered tyres were 14,295 and 16,060 Mg, respectively, with a total amount of 32,741 Mg. For generated tyres, the average amount was the lowest at 3,950 Mg (Table 2).
The highest correlation value of 0.90 occurred between the total tyres amount and recovered tyres. The correlation value of 0.73 between the total number of tyres and collected tyres was high. The recovered tyres correlate with the collected tyres (0.43), which is a moderate correlation. The remaining relationships between the collected tyres and number of generated tyres, the total quantity of collected and generated tyres, and the recovered tyres did not exceed 0.4 (Table 3).
Table 3
Correlation between variability of amount generated, collected and recovered used tires
Tires | | | | |
| | 0,90 | 0,73 | 0,30 |
| 0,90 | | 0,43 | 0,04 |
| 0,73 | 0,43 | | 0,38 |
| 0,30 | 0,04 | 0,38 | |
aItalic value of statistics means that the relationship is statistically significant at p < 0.05 |
However, the trend study confirmed only a statistically significant increase in the generated tyres and a decrease in the collected tyres (Table 4).
Table 4
Time trends of generated and collected waste tires
Variable | Trend | Probability (p) |
Collected tires | ↓ | 0,01 |
Generated tires | ↑ | 0,02 |