A Study on the Default Supplemental Adjustment Factors of Progression Adjustment Factor Formula under Non-Lane Based Traffic Condition

Abstract

A mathematical expression of supplemental adjustment factor (fPA) has provided a way to estimate Progression Adjustment Factor (P.F.) more accurately as the P.F. relies on the fPA value. The mathematical formula of fPA requires traffic parameters that need to be determined from the field survey. As non-lane based traffic behavior is significantly different from lane-based traffic, this study examines the applicability of the default fPA values of Highway Capacity Manual-2000 under the non-lane based traffic condition. Default values for all six Arrival Types (AT1 to AT6) are reviewed against an available mathematical expression. After performing statistical analysis on the collected data, it is found that the HCM-provided default fPA values for AT1, AT3, AT5 and AT6 are consistent with the mathematical expression. However, the supplemental factors for AT2 and AT4 are found to vary significantly from the default values. By considering the mathematical expression as a standard of comparison, a graphical representation of error corresponding to trial fPA value shows that a value of 0.99 for fPA provides the minimum error of P.F. for AT2. Thus, the default value (fPA =0.93) is found to underestimate fPA as well as P.F. by 6.5%. In a similar way, the fPA value for AT4 is found to be 0.96 which is 16.5% less than the default value. So, the default value (fPA =1.15) overestimates fPA and P.F. by 16.5%. Therefore, fPA = 0.99 for AT2 and fPA = 0.96 for AT4 should be used to estimate P.F. in case of non-lane based traffic.