This paper presents a comprehensive analysis of a two-span post-tensioned prestressed concrete cellular box girder bridge deck, focusing on the effects of dead load, moving load, and prestressing across various span lengths (30m, 40m, 50m, 60m, and 70m) and different span-to-depth (L/D) ratios of 23, 24, 25, 26, and 27. The study follows the limit state method as per IRC 112-2011 guidelines. Key parameters analysed include bending moments, shear forces, and top fibre stresses. The research aims to identify the optimal L/D ratio that balances structural efficiency and material usage. The results indicate that an L/D ratio of 25 provides the most balanced design, achieving the best combination of structural performance, material efficiency, and economic viability. This ratio minimizes material usage while maintaining adequate structural integrity and avoiding excessive prestressing forces. The paper also includes a detailed comparison of manual versus software-based calculations for bending moments, shear forces, and deflections. The findings show that while software calculations tend to predict lower deflections and higher shear forces for both shorter and longer spans, the manual calculations align closely with the software results for intermediate spans. The top fibre stress analysis further confirms that all designs remain within permissible limits, ensuring safety and compliance with relevant standards. Overall, the study reinforces the suitability of the L/D ratio of 25 as the optimal choice for designing two-span prestressed concrete box girder bridge decks, offering a robust framework for future design considerations.