2025 Volume 66 Issue 2 Pages 96-101
Currently, mowers are widely used for weed control along railway tracks. However, this method has some issues. For example, one of issues is that weeds regrow quickly after being cut during summer. Therefore, there is a need for more effective and efficient weed control methods. To address this need, we developed a specialized piece of steam weeding equipment. This equipment consists of a general-purpose steam cleaner and newly developed handheld nozzles. To verify the effectiveness of the developed equipment, it was tested in areas with vigorous weed growth. The test showed that this equipment provided effective usability with less labor and time. Furthermore, it was also confirmed that large weed regrowth was reduced by 70% after one year compared with mowers.
Railway field from outside the tracks to the boundary of the field is overgrown with weeds (Fig. 1), so bush cutter (mowing) is used as part of railway environment management. Mowing can temporarily remove weeds; however, weeds regrow in a relatively short period during summer. Mowers are vibrating tools, which have restrictions on the working time to prevent health problems. Thus, the amount of daily work is limited (consecutively 30 minutes, and totally 2 hours per day in Japan). Health problems, such as workers temporarily losing their hearing owing to the noise of mowing, have been reported [1]. Other issues include the presence of signaling and communication cables for train operation, which requires advance searching for preventing the cables from being cut by the rotating blade of the mowing.
Other weeding methods include the spraying of herbicides, which chemically inhibit the photosynthesis and growth of weeds. The spraying of herbicides is highly effective, but the risks of the scattering or runoff of herbicides off-site need to be considered, and their use needs to be limited depending on the environment along the railway tracks. Thus, there is a demand for a weeding method that is safer and has a lower environmental impact while ensuring ease of application and effectiveness.
Therefore, we focused on “steam weeding,” which uses heat to kill weeds by causing thermal denaturation of their proteins. We decided to develop a steam weeding method that is easy to apply and extremely effective.
As this method uses steam (water), there are no environmental impacts, as is the case with spraying herbicides. This method is also expected to kill ungerminated seeds [2], which cannot be achieved by mowing or spraying of herbicides.
Figure 2 shows the equipment for the developed steam weeding method. The equipment consists of one general-purpose steam cleaner and two sets of newly developed handheld nozzles. As shown in Fig. 3, all the necessary items, which include a plastic tank filled with water for refills, can be loaded and transported on a truck with a surface area of around 3 m2.
Steam weeding was originally developed in the agricultural field as a technique for sterilizing and disinfecting soil. It generally uses tap water, so the steam generation source (boiler) is large. A large quantity of water is required (around 1000 L/h), and a boiler engineer’s license is required for operation.
However, this equipment is impractical for use in a railway environment, where the use of tap water is difficult and practical application requires limiting the water consumption to the number of tanks with a capacity of approximately 20 L. Therefore, we first selected a boiler with a water consumption rate that would be suitable for steam weeding in a railway environment. By investigating domestic commercially available products, we selected a general-purpose steam cleaner with a water consumption rate of 72 L/h, which is less than a tenth of the amount generally used in the agricultural field. The selected product does not require any qualifications for operation and can be started with a 100 V power source.
Larger models than the selected product were excluded because they consume more water (over 1000 L/h), require qualifications for operation, and need a 200 V power source. Smaller models which consume significantly less water (steam volume) at only a few liters per hour, were excluded because we concluded they would be unsuitable for removing the large weeds that grow on railway field.
2.2 Investigation of the shape of the handheld nozzleWe investigated the handheld nozzle based on the performance of the boiler. Work aimed at sterilizing and disinfecting soil in agricultural contexts involves covering the area of farmland to be treated with a sheet of a certain size and filling the area under the sheet with steam for several hours. Transposing this method to a railway environment, in areas which contain other facilities like electricity poles, would make the process time-consuming depending on the type of facilities in each location. There are also concerns that sheets may be blown away by wind. Therefore, we developed a handheld nozzle method that could respond in a flexible manner to the condition of the facilities and could process a unit work area (area of a cover part) within 10 seconds, considering the mowing time as a reference.
Figure 4 shows the developed handheld nozzle. The developed product is designed to release and retain steam supplied from the boiler through a hose inside the cover, ensuring heating efficiency while reducing water consumption (steam volume). The cover has lattice-shaped ribs (convex parts) that serve as a path for steam diffusion when densely grown weeds are covered to enable efficient heating.
We also investigated the shape of the steam outlet along with the cover. Figures 5 and 6 show the initial and final specifications of the steam outlet shape and their heating characteristics, respectively. The initial specification had a cover area of 0.16 m2, with general slit shape used to exhaust steam downward from the top of the cover. The final specification involved inserting a cylindrical pipe into the weeds and spraying steam sideways near the ground surface toward the roots of the weeds. The cover area was also expanded 3.1 times (0.49 m2) to improve speed of work.
The heating characteristics were measured by placing thermocouples (total of five points) on the ground surface at the four corners and center of the cover, and the temperature increased almost uniformly at all five points. The five-point average value is shown in both figures. Additionally, the thermal denaturation of proteins will definitively occur at 60°C. A study on the thermal denaturation of the cell membrane structures at high temperatures [3] reported that the cell membrane rapidly expands in volume at approximately 50°C. Research has also reported that immersion in water at 60°C for 2 seconds will cause stems and leaves to die. Therefore, 60°C was set as a benchmark at which weeds will die because of stem and leaf cell death. The study that tested the effect of the product on seeds in farmland [2] confirmed that the seed killing effect was observed at 90°C.
As shown in Fig. 5, the initial specification reached a temperature of 60°C in approximately 1 second, but insulation by the weeds in the top section delayed the process by 14 seconds to attain a temperature of 90°C. On the other hand, as shown in Fig. 6, the final specification reached a temperature of 90°C in approximately 5 seconds.
We also evaluated the working environment in terms of noise by measuring the working noise of the equipment (equivalent sound level LAeq). The results indicated a value of 59.7 dB (1.5 m height) at ear level of the worker holding the handheld nozzle, 67.6 dB (ground level) 100 mm away from the cover of the handheld nozzle when spraying steam, and 67.0 dB (1.5 m height) 1 m away from the boiler during water heating. These values are sufficiently low not to disrupt conversations during work.
In order to determine the effect that timing of steam weeding (weeding season) had on weed regrowth, we conducted a test setting weeding method and weeding season as parameters.
We conducted the test in a location where Imperata cylindrica, a perennial weed of the Poaceae family, commonly grows. We prepared test plots measuring 2.2 m × 1.5 m, and weeding work was performed from spring to autumn in each test plot. The weeding season and weeding method were considered as parameters. The weeding method involved not only steam weeding but also mowing for comparison.
Mowing was done manually using shears to prevent seeds from scattering to other test plots and to keep the grass height within the plot constant after weeding. Actual work using a bush cutter involves raising the blade to a certain height above the ground surface to prevent flying stones as a result of contact with the blade. Crushed stone (maximum particle size of 63 mm) used for ballast beds may fall and scatter on railway field, so the target weed height for the shears was set at 63 mm from the ground surface. During mowing, the cut parts were disposed of as industrial waste.
During steam weeding, we used a handheld nozzle, as shown in Fig. 5. Given the relationship between the timing of this test and development of the handheld nozzle, the steam injection time was set at 5 seconds. As with herbicide spraying, steam weeding involves the stems and leaves being left to die and wither naturally in place without being separated from the roots, so they were left behind. As shown in Fig. 7, the weeds, which were compressed in place immediately after steam weeding, died after a few hours while still compressed.
The measured items were the maximum plant height and vegetation coverage of each test plot. The maximum plant height was normalized by dividing the value by the maximum value during the test period. The vegetation coverage was the ratio of the area occupied by weeds in the plot (Fig. 8) and was visually measured (excluding dead weeds). The experimental results were calculated by multiplying the normalized maximum plant height by the vegetation coverage, and this was considered as the weed regrowth extent. The measurements were recorded after the weeding work (next day, and 1-2 weeks later), and then at approximately monthly intervals.
Figure 9 shows the measurement results of the weed regrowth extent. The weed regrowth extent was not 0 on the weeding day (Day 0) in the mowing results because weeds with a target height of less than 63 mm that were not mowed remained in the plot. The mowing results showed that regrowth began immediately after the weeding regardless of the work timing. For summer work, complete regrowth occurred approximately 60 days after weeding.
The steam weeding results showed that weed regrowth was suppressed for approximately 15 days after weeding in the spring and summer, and the number of days until complete regrowth tended to be longer than that with mowing. For autumn work, mowing results in about 50% regrowth, whereas steam weeding only resulted in about 10% regrowth. Steam weeding was more effective than mowing for all seasons.
The difference in regrowth was attributed to the fact that mowing avoids the sprouts near the ground surface, which regrow immediately, whereas steam weeding involved heat acting on the entire stem and leaves of the weeds, including the sprouts. Additionally, as shown in Fig. 7, steam weeding resulted in weeds covering the ground and blocking sunlight, which may have delayed regrowth owing to the shading effect. This experiment was not conducted in a railway environment, so a field test was subsequently conducted to verify the effectiveness of the equipment along a commercial line.
We confirmed the workability and weeding effect of the final developed equipment by conducting a field test along a commercial line. The field test was conducted in an area where the large weed Solidago altissima grows in clusters during the summer (July). Additionally, we set up a field where mowing was conducted in an adjacent location as a comparison. Solidago altissima is a perennial weed of the Asteraceae family that is known to form large communities and can be difficult to control [4].
The work speed, excluding post- and pre-work, were 4.0 m2/min per mowing. The work speed was 5.0 m2/min per handheld nozzle for steam weeding, confirming that the work speed was 1.25 times faster than mowing.
When looking at the work site approximately three months after the work (October), the mowed plots (Fig. 10) showed Solidago altissima regrowing in about 80% of the area where weeding was conducted, with flowering being observed. In contrast, in the steamed plots (Fig. 11) Solidago altissima regrowth was limited to approximately 10% of the work area with no flowering. As in the previous section, regrowth was thought to have been hampered because steam weeding acts on all stems and leaves on the ground surface, and no new sprouts that could regrow remained. As in the previous section, the steam-weeding effect observed was greater than for mowing, but was also greater than the summer results in the previous section. This was thought to be due to the effect of different weed species as the test in the previous section was conducted in an area where there was an overgrowth of Imperata cylindrica.
Furthermore, long-term effects were confirmed by measuring the number of remaining Solidago altissima plants in an arbitrary 1 m2 area one year later. The number of plants in the plot subjected to mowing was 89 plants/m2 compared to 25 plants/m2 in the plot where steam weeding was conducted. This confirms that the number of remaining large weed plants one year after application had decreased by approximately 70%. Research indicates that mowing needs to be conducted at least three times a year to control Solidago altissima [4], but one steam weeding work session reduced the number of remaining plants one year later. This is because steam weeding was effective in killing seeds along with stems and leaves on the ground.
The abovementioned results were obtained in the summer, but steam weeding is expected to have a similar effect in other seasons as the method is expected to achieve effects against seeds that cannot be achieved by mowing.
Work was also conducted on the same day in other locations to those shown in Fig. 10 and Fig. 11, and the number of plants was measured one year later in the same manner. Similar results were obtained for regrowth. The number of remaining plants after one year was 109 plants/m2 for the plot where mowing was conducted, and 24 plants/m2 for the plot where steam weeding was conducted. Overall, we confirmed a reduction of approximately 80% in other locations.
We considered the work efficiency of the weeding method by estimating the work time for mowing and steam weeding from the work rate obtained in the field test. We assumed a general work area of 300 m2 and calculated the time required from the start to the end of the work. For mowing, we assumed a work party of 5 people, including three workers to operate three mowers and two workers to search for signaling and communication cables laid within the site and to collect cut grass. For steam weeding, the equipment consisted of one boiler and two handheld nozzles, so we assumed a work party of 3 people, including two operators for the handheld nozzle operators and one boiler monitor/water supplier. The measurement results from the previous section were used as a reference to estimate the work time: 4.0 m2/min per mowing and 5.0 m2/min per handheld nozzle.
Figure 12 shows the work time estimation results. Mowing required advance work to search for cables and follow up work to collect the cut grass. Thus, the total time required was 72 minutes.
Meanwhile, the time required for steam weeding was 22 minutes less, for a total work time of 50 minutes. The results showed that steam weeding improved the work rate by 44% compared to mowing while reducing the number of workers required from 5 to 3, or by 60%. The breakdown of work showed however that the time required for actual weeding using steam was longer than actual mowing owing to the use of three mowers for two handheld nozzles. However, when taking into account preparation and cleaning, the overall work time was shorter for steam weeding.
We developed a steam weeding method that combines a general-purpose steam cleaner with a newly developed handheld nozzle. Our equipment provides a practical, environmentally friendly solution for weeding in a railway environment. It reduces labor, improves work efficiency, and delivers better long-term weed control compared to conventional mowing methods. The equipment successfully controls large weeds with just one treatment per year, compared to multiple interventions needed with mowing, representing a significant advancement in railway weeding technology.
While our current research focused on areas outside actual railway tracks, we have begun developing an extension of our method that can be towed along the tracks to control weeds growing between them. This adaptation promises to further improve weeding in the railway environment.
We would like to thank all the individuals involved at the Kyushu Railway Company for their cooperation in conducting the field test and the follow-up observations in this study. We would like to express our sincere gratitude for their assistance.
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Hikaru TANIGAWA
Assistant Senior Researcher, Track Structures and Geotechnology Laboratory, Track Technology Division (Former) Research Areas: Ballastless Track, Ballasted Track |
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Tomoyoshi USHIOGI
Senior Researcher, Comfort Science and Engineering Laboratory, Human Science Division Research Areas: Chemical Engineering |
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Masateru IKEHATA, Ph.D. Senior Chief Researcher, Comfort Science and Engineering Laboratory, Human Science Division Research Areas: Genotoxicology, Cell Biology, Microbiology |
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Takahisa NAKAMURA, Dr.Eng. Chief Researcher, Track Structures and Geotechnology Laboratory, Track Technology Division Research Areas: Ballasted Track, Roadbed Structure |
