Potential methods to forecast the actual highway capacity

Measurements at "capacity situations" on freeways in the Netherlands of the maximum flow per 15 minutes, called the actual capacity, showed coefficients of variations from 3-12% for normal conditions. These variations seem not to be due to chance only, therefore forecasting of the actual capacity is of vital importance for traffic management measures like route diversion and ramp metering. In the paper an overview of possible methods to forecast actual capacity is given, with special attention to methods based on the decomposition of the distribution of headways into followers and non-followers. The inverse of the mean of the headways of the followers, measured at flows below capacity, can be used for the actual capacity estimation. Microscopic analysis of traffic over a road length of 1200 m has been the validated reference, mentioned the Pendel Following Criterion (PFC), for the investigation of this type of capacity estimators. With herefrom derived simple capacity estimators, capacity profiles have been made at lane drops and entrance lanes.