Chapter 9 of the 1985 Highway Capacity Manual (HCM), Transportation Research Board Special Report 209, uses average stopped delay per vehicle as the sole determinant to establish threshold criteria for defining levels of service at signalized intersections. Of all the variables impacting delay, quality of progression has the largest potential effect as evidenced by the wide range of progression adjustment factors (PFs), 0.40 to 1.85 in Table 9-13 of the HCM. These PFs are based on limited field data, and selection from a reasonable range of PFs in the table often results in changes in the level of service designation for the approach. In addition, guidelines for selecting the appropriate PFs to apply in practical applications are difficult to interpret. Because of these concerns, a project was conducted to evaluate the effects of changes in the quality of traffic signal progression on stopped delay. Dependent variables investigated included signal offset and spacing, cycle length and splits, bandwidth, platoon volume, volume-to-capacity ratios, arterial speed, and platoon dispersion. Primary emphasis was given to through movements at pretimed signals on multilane arterials in urban and suburban areas. Secondary emphasis was given to the same conditions under semiactuated control. Products of the research are: (1) A revised uniform delay equation which includes a term for quality of progression; (2) A calibrated set of progression adjustment factors in the form of a revised version of Table 9-13; (3) A continuous relationship for estimating the progression adjustment factors in the revised version of Table 9-13; and (4) A methodology for estimating the proportion of the total volume arriving on green, platoon ratio, and/or arrival type. This material is suitable for application to the general stopped delay model of Chapter 9 and to the urban arterials procedure in Chapter 11 of the 1985 HCM.
Samenvatting