ESTIMATING TRAVELING TIME/SPEED
传统上把平均行驶速度当作常数，但本文提出用分段线性函数更合理地近似速度，并同时确定断点和平均速度，对路径规划中准确估算行驶时间有帮助。
Traditionally treated as a constant, average driving speed and class of road is more reasonably approximated as a piecewise linear function of the distance traveled. Presented here are methods for determining the breakpoint and the corresponding average speeds simultaneously. It is important to estimate travel times correctly in route planning in order to guarantee reasonable workloads for drivers and to meet promised delivery times. Estimating travel time is equivalent to estimating the travel speed. Most route planning applications assume that speeds are constant for an area, class of road or period. The data examined indicate that this assumption is not realistic for shorter distances. Data from New York and Atlanta were used and indicate that driving speeds are not constant, mean speeds increase linearly and then level off and there are significant variations in driving speeds.