This paper presents a novel definition of drivers’ safety margins reflected in speed profiles on a tangent to curved road design. These safety margins are based on a vehicle dynamics model, which is implemented to assess the speed variation at impending skid conditions from tangent to curve on the basis of several parameters. This model returns the theoretical speed-distance curve corresponding to the driver’s maximum safe speed and acceleration when utilizing the outmost of the available vehicle horse power. On the basis of actual vehicle speed profiles, the model also returns the respective curve for the actual speed-distance i.e. the utilized share of vehicle horse power, which reflects the driver’s safety margin. Data from a driving simulator experiment are used to test the proposed methodology, explore driver’s speed profiles and the parameters affecting drivers’ safety margins. The results suggest that drivers’ safety margins towards the examined curve are considerable, with the majority of the drivers using less than 55% of the available vehicle horse power. Drivers can be grouped into “aggressive”, “moderate” and “conservative” speeding behaviour, each group exhibiting distinct initial speed, “breakpoint” distance and acceleration / deceleration patterns. Higher initial speed is positively correlated with more aggressive driving i.e. lower safety margins. On the contrary, a higher safety margin was associated with earlier deceleration before the curve. The proposed approach yields a continuous and objective assessment of driver speeding behaviour from tangent to curve and the related safety margins, both for individual drivers, as well as for groups of drivers with similar speeding patterns.