Yasushi OBATA

Study on the pavement structure of a dedicated BRT road using an existing ballast track

Osamu TAKAHASHI

The maintenance of local public transportation in Japan has become increasingly difficult due to population decline and aging. As part of efforts to sustain regional transport systems, some discontinued railway sections have been converted into Bus Rapid Transit (BRT) routes. However, conventional pavement structures for BRT-exclusive roads require newly purchased graded crushed stone for the base course, leading to higher construction costs. To address this issue, an alternative pavement structure has been proposed, taking advantage of the low traffic volume on BRT-exclusive roads. In this structure, the existing railway ballast is reused as a base course after cement stabilization, the subgrade remains as in-situ ground, and an asphalt concrete (AC) layer is paved directly on top. This approach eliminates the need for a new graded crushed stone base, thereby reducing construction costs. Nevertheless, concerns exist regarding strength variability in the AC layer due to the large aggregate size and surface irregularities of the ballast.
This study mechanically evaluated the AC layer used in the proposed pavement structure and quantified key design indicators for structural design. Test results showed that the lower part of the AC layer placed on an uneven surface had lower compaction and durability. By dividing the AC layer into a surface layer 60% and a base layer 40%, a theoretical design based on multilayer elastic theory was conducted. The results indicated that an AC thickness of at least 80 mm satisfies structural performance requirements under low traffic conditions.
A comparative evaluation revealed that the proposed structure can reduce construction costs by over 50% and shorten the construction period by approximately two weeks, although CO₂ emissions increased by about 17%. Overall, the proposed pavement structure ensures structural safety while achieving significant cost and time savings.