Ensuring sufficient road surface friction is essential for maintaining traffic safety, particularly under adverse weather conditions. However, the current Korean design standards for the longitudinal friction coefficient (LFC) are primarily derived from foreign guidelines with limited empirical validation under domestic road and climatic conditions. This study aims to generate field-based LFC data across a range of road surface types and vehicle speeds and evaluate the appropriateness of the LFC values currently adopted in national road design standards. The field experiments were conducted at the Yeoncheon SOC Proving Ground. The five representative road surface conditions were dry, wet, slush, compacted snow, and icy. Driving tests were conducted for each surface condition at four speeds (30, 40, 50, and 60 km/h) using a test vehicle equipped with continuous friction measuring equipment. Twenty scenarios were tested with multiple repetitions to ensure statistical reliability. Consequently, the average LFC values were 0.748 for dry, 0.615 for wet, 0.232 for slush, 0.173 for compacted snow, and 0.133 for icy conditions. The results showed that road surface conditions had a significantly greater impact on the LFC than vehicle speed. Moreover, the values measured under low-friction conditions were consistently lower than those specified in the current Korean standards. These findings highlight the need to revise the existing LFC design values to better reflect domestic winter road environments. The data can also inform the development of road safety strategies such as variable speed limit systems, autonomous vehicle control algorithms, and automatic emergency braking systems suitable for winter operations.