Several safety studies and accident database suggest that stronger consideration should be dedicated to night driving conditions.

The prediction of operating speeds is strongly recommended to evaluate design consistency, highlighting abrupt changes in the roadway's features which can determine surprising events and lead to accident.

Nowadays predictive models of operating speed and speed differentials are focused on daytime driving conditions, neglecting nighttime driving conditionings.

In this study we compare and model driver operating speeds and speed differentials in simulated day and night driving, identifying the significant factors that influence speed behavior under different lighting conditions of the road environment.

We propose new predictive speed models for tangent and curve as well as speed differential models, differentiated for daytime and nighttime driving, highlighting the effects of different geometric predictors under different visibility conditions.