Operating speed models for horizontal reverse curves

The operating speed variation in horizontal reverse curves is a problem of relevance to road safety. If the speed variations are high and the tangent between the curves is short, then the crash risk increases. the operating speed can be predicted using operating speed profile models that correlate the operating speed with the radii and tangents of the horizontal reverse curves. This study proposes a new operating speed model for horizontal reverse curves using speed data obtained with a 10 Hz Global Positioning System logger. Speed, heading and position data were collected for 30 runs per site at 34 test sites. Tangent lengths, deflections, curve lengths and radii were also obtained. The operating speed models were calibrated using eight points along the reverse curves measured. The standard errors obtained in the selected models ranged between 3·0 and 6·6 km/h, the root mean square error ranged from 0·6 to 2·7 km/h, and the R² value of individual speed–geometry models varied between 0·52 and 0·99. The models obtained allowed engineers to ascertain the operating speed profile at the horizontal reverse curve and to study the effects of different design alternatives on the operating speed.