Progression adjustment factors for uniform delay at signalized intersections

Signal progression plays an important role in controlling arrival pattern and delay at coordinated signalized intersections. In the Highway Capacity Manual (HCM), one random and five nonrandom arrival types are identified. The delays for nonrandom arrival cases (platoon arrivals) are computed by applying progression adjustment factors (PFs) to the delay for the random arrival case. However, HCM-estimated delays are found to be significantly different from field-measured delays for Arrival Types 1, 4, and 6. For Arrival Type 2 the HCM estimations are acceptable, although the deviations are still relatively high. For Arrival Types 3 and 5 the HCM estimates the delays accurately. These findings suggest that the HCM PFs need to be revised. A new set of PFs was developed using the arrival-based delay models. A relationship between the effective green ratio, g/C, and the new PFs was established for each arrival type. With the proposed PF values, the HCM approach would be more accurate than it is with the current PF values. For Arrival Type 1, the new PF values are higher than the current HCM values for g/C≤0.50 and lower for g/C>0.50. For Arrival Types 2 and 4, the new PF values are lower than those of HCM, as expected, because the HCM overestimates the delays for both Arrival Types 2 and 4. For Arrival Type 6 the new PF values are lower for g/C≤0.40; otherwise they are higher. A new progression adjustment table similar to Table 9-13 of the HCM is created. It is recommended that the new PF values be adopted by the HCM since they enhance the accuracy of delay estimation.