T Toll road infrastructure development requires innovations in design and construction methods that can improve cost efficiency and accelerate project completion without compromising structural quality and safety. this study aims to analyze the effects of top management, human resources, technical factors, and external factors on project cost efficiency and to examine the effect of cost efficiency on project completion time in the implementation of the precast half-slab design in the serang–panimbang toll road project. a quantitative descriptive method was employed using primary data collected through a closed-ended five-point likert-scale questionnaire and secondary data consisting of design drawings, load calculations, unit price analyses, and project material and volume records. the sample was selected through census or total sampling and comprised 58 construction professionals, consisting of 33 respondents from the serang–panimbang toll road project and 25 respondents from the bayung lencir–tempino toll road project. relationships among the variables were analyzed using structural equation modeling–partial least squares with smartpls 3.2.9, complemented by a technical assessment and a cost-time comparison between the full-slab cast-in-situ and precast half-slab methods. the results demonstrate that top management (β = 0.273; p < 0.001), human resources (β = 0.366; p < 0.001), technical factors (β = 0.272; p = 0.001), and external factors (β = 0.097; p = 0.005) have positive and significant effects on project cost efficiency. cost efficiency also has a positive and significant effect on project completion time (β = 0.540; p < 0.001). the model explains 98.8% of the variance in project cost efficiency and 97.6% of the variance in project completion time. the technical assessment indicates that the precast half-slab design is feasible based on the evaluated moment, shear, and deflection parameters. for the two-span/mr-ps analysis unit, the method generated total cost savings of idr 274,524,671.00, equivalent to 2.02%, while the estimated savings for 45 spans reached idr 12,353,610,190.85. the construction duration was reduced from 461 days to 250 days, representing an acceleration of 211 days or 45.77%. therefore, replacing the full-slab cast-in-situ design with a precast half-slab system represents a feasible value-engineering strategy for optimizing project costs and completion time, with human resources identified as the most influential factor in improving cost efficiency.