The concept of maximizing two-way progression to compute signal-timing plans for signalized arterials has been used for 60 years. One of the unknown questions that exists is how the available two-way band should be apportioned between the two directions of traffic flow. Until now, the two directions have been weighted in proportion to the ratio of the average volume in each direction. However, preliminury otudieo huve indicuted thut it would be better to apportion the two-wuy progression bandwidths than to use the volume-ratio criterion alone. Described is a bandwidth weighting algorithm that is based on delay. A simple delay model developed for the PASSER II program was used to estimate delay. Through extensive testing, using the NETSIM model on nine real-world arterial data sets, it was found that three different expressions for the bandwidth ratio should be used; which expression was to be used depended on whether the directional volume ratio was less than 0.45, between 0.45 and 0.55, or more than 0.55. All three expressions involve the ratio of delay in the two directions. A blind test was performed by using six scenarios based on two real-world arterials that were not included in the nine test arterials used for preliminary testing. Based on comparisons using the NETSIM model, the result of this blind test indicated that the weighting algorithm developed in this research generally performed better than both the arbitrary equal-weighting and the MAXBAND average volume-ratio criteria, which have been used up to now.

The concept of maximizing progression bandwidth as the criterion for calculating optimal offsets in arterial signal systems has been used for approximately 60 years. At first, graphic manual methods were used. With the introduction of the digital computer, the bandwioth optimization problem was computerized, and a number of programs were developed (1, 2). Two of them, MAXBAND and PASSER II, also optimize the left-turn phase sequence (3, 4). Both programs can weight the bands to provide-a wider progression band in one of the two directions. Neither of them, however, provides any guidelines for adjusting the weighting factor other than to suggest setting it equal to the ratio of the average volumes in the two directions. Recent feasibility studies conducted by the FHWA, US Department of Transportation, have indicated that proportioning the total two-way bandwidth in the ratio of volume distribution does not provide the lowest systemwide delay. The FHWA feasibility study also indicated that the fundamental causal factors and general relationships existing between bandwidth ratio and delay could not be accurately predicted, based on current technology in arterial traffic signal-timing optimization.