This study characterises the subsurface along a highland road corridor in northern Sarawak using electrical resistivity tomography (ERT) as a complementary tool to standard penetration testing (SPT). The corridor is underlain mainly by argillaceous and arenaceous sedimentary rocks. A total of 16 paired ERT–SPT profiles were examined across four construction packages. ERT data were acquired using a Wenner–Schlumberger array and inverted in ResIPy. The resistivity at each borehole location is compared with the soil and rock layers logged in the SPT boreholes and checked against published resistivity ranges for earth materials, and the measured values were compiled as package-specific resistivity index ranges. Because the ERT surveys were carried out before the SPT drilling, groundwater levels in the boreholes could not be related directly to the resistivity values. Resistivity varied widely between packages. Weathered bedrock gave about 429–1,729 Ω·m in Package 1, 2–36 Ω·m in Package 2 and 100–565 Ω·m in Package 4, whereas Package 3 returned values above 10^5 Ω·m that are treated with caution. In several profiles resistivity decreased with depth while SPT N-values increased, so high resistivity was not a reliable sign of competent ground. Ranges overlapped between materials and between packages, reflecting the combined influence of moisture, clay content, pore-water chemistry and weathering. Very low resistivities (< 1 Ω·m), which may indicate sulphide-bearing material and a potential risk of acid mine drainage, were found in only one section and require laboratory confirmation. These findings confirm that ERT cannot replace SPT, which remains essential for soil classification and design parameters. Once calibrated against borehole data, however, ERT extends that information laterally and helps identify weak or saturated zones between boreholes. The index ranges were not tested against independent boreholes; they are specific to the investigated corridor and should be treated as a guide for preliminary interpretation until checked against new borehole data.