Chapter 16 of the Highway Capacity Manual 2000 (HCM 2000) includes models and procedures for calculating capacity and delay at signalized intersections. However, the procedures do not provide estimation of the optimal cycle length which would result in the minimal intersection delay. A quick estimation method for determining the cycle length is described in Appendix A, Chap. 10 of the HCM 2000 for planning level applications. In this method, a simple equation is used to estimate the cycle length if it is not available. However, the estimated cycle length may not be the optimal cycle length from the point of view of achieving minimum intersection delay. To develop a new cycle length model, the Webster’s minimum delay cycle length model is first considered. However, based on our study, Webster’s minimum delay cycle length model overestimates the optimal cycle length compared to the results from the HCM 2000 delay calculation method, especially under high traffic volume conditions. After investigating three new models developed during this study, an exponential-type cycle length model is recommended. Based on a series of CORSIM simulation runs, the cycle length predicted by this model provides better results than the current quick estimation method of the HCM 2000.

Although rain and other precipitation is common, analyses of signalized intersections based on the Highway Capacity Manual require clear weather and dry pavement conditions. Three factors may be affected by wet weather: saturation flow, effective green time, and progression. Saturation headway may lengthen, effective green may shrink, and progression may worsen in wet conditions. As a result, signalized intersection operations become less efficient. This is demonstrated in the longer delays estimated for five sample intersections. A methodology was developed for the derivation of the probability of rainfall $\left(P_{\text{wet}}\right)$ during the morning and evening peak hours for any intersection in the United States using readily available rainfall accumulation data from the National Oceanic and Atmospheric Administration. Once delay and level of service (LOS) are estimated for both dry and wet conditions, a weighted average is employed for estimating delays and LOS that represent the prevailing dry and wet peak period conditions at a signalized intersection.

Past research has indicated that the accuracy of traffic quality studies strongly depends on capacity parameters, particularly when demand approaches capacity. Minimal work has been done in the past on local values of the base saturation flow rate and lost times used in capacity analysis of signalized intersections. This paper discusses saturation flow studies conducted for Indiana. The results confirm that the default parameters recommended by the Highway Capacity Manual, such as the heavy vehicle equivalency factor and the protected left-turn adjustment factor, are adequate for Indiana. At the same time, the base saturation flow rate was found to vary strongly across locations, even when the geometry and traffic conditions were nearly identical, indicating that there are other factors not yet included in the Highway Capacity Manual. Regression analysis of the saturation flow rate variability identified the size of a town to be a good predictor. A model was developed and a set of base saturation flow rates were proposed, which depend on the number of lanes and the town population. The estimated impact of the size of the town estimated for Indiana is very close to the values obtained in the past for other states. The paper provides a convincing argument for adding to the Highway Capacity Manual a population adjustment factor for saturation flow rates.

Appendix C of Chap. 16 in the Highway Capacity Manual 2000 (HCM 2000) discusses the method for calculating the left turn factor for permitted left turns. This method uses the queue clearance model, represented by equation C16-6 of the HCM 2000 to calculate the left-turn factor. This paper reports on a study of the accuracy of this queue clearance model to predict observed clearance times. For this study, queue clearance times were observed for multiple-lane approaches with shared left turns and opposing multiple-lane approaches for five study intersections located throughout Missouri. Data collected at each intersection were used as inputs to the HCM 2000 queue clearance model to predict queue clearance times. A comparison of the predicted queue clearance time and the observed queue clearance time found that the HCM 2000 queue clearance model underestimates observed clearance times on average by $5.8\mathrm{s}$ . Further research is needed to identify the source of this bias and to recommend improvements to the HCM 2000 model.

For oversaturated traffic conditions, control delays from CORSIM simulation were compared to the Highway Capacity Manual (HCM) 2000 delays for zero and nonzero initial queue conditions for arrival type (AT) 1, 2, 4, and 5 at three different degrees of saturation, 1.02, 1.1, and 1.2. For zero initial queue condition, HCM delays for AT-1 were lower than CORSIM delays except at a degree of saturation of 1.02, at which they were similar. For AT-2, HCM delays were statistically similar, except at degree of saturation 1.1. For AT-4 and AT-5, HCM delays were consistently higher than CORSIM delays for all degrees of saturation. For nonzero initial queue condition, HCM delays were consistently lower than CORSIM delays for all degrees of saturation for AT-1. For AT-2, HCM delays were similar to CORSIM delays only at degrees of saturation 1.1 and 1.2. For AT-4 and AT-5, HCM delays were higher than CORSIM delays for all degrees of saturation.

Road designers in Poland use capacity methods presented in subsequent issues of the Highway Capacity Manual (HCM). The new HCM 2000 gave an impulse for research aimed at evaluating adequacy of the default parameters of the HCM capacity models to the Polish conditions. Studies were conducted in several Polish towns and cities to investigate capacity of minor movements at two-way stop-controlled intersections, two-way yield-controlled intersections, and at roundabouts. The results have allowed developing equations of basic capacity parameters, i.e., critical time gap and follow-up time and calibrating the models to the local conditions. The paper presents these results and recommends how to adapt the HCM 2000 method to the Polish conditions.

Traffic engineering studies such as validating Highway Capacity Manual (HCM) models require complete and reliable field data. However, the wealth of intelligent transportation systems (ITS) data is sometimes rendered useless for these purposes because of missing values in the data. Many imputation techniques have been developed in the past with virtually all of them imputing a single value for a missing datum. While this provides somewhat simple and fast estimates, it does not eliminate the possibility of producing biased results and it also fails to account for the uncertainty brought about by missing data. To overcome these limitations, a multiple imputation scheme is developed which provides multiple estimates for a missing value, simulating multiple draws from a population to estimate the unknown parameter. This paper also develops a framework of imputation which gives a broad perspective so that one can relate imputation methods to each other.

The Highway Capacity Manual (HCM) 2000 equation for pedestrian delay at signalized intersections assumes that pedestrian arrivals at those intersections are random. However, if a significant percentage of those pedestrians are arriving from an upstream coordinated signal, the arrival rate may not be random and the average delay may be quite different from that which would be predicted. Two studies were conducted to test the HCM model for pedestrian delay at coordinated signalized intersections. Data collected at six intersections in St. Louis indicated that pedestrian arrivals at these locations were significantly affected by upstream signals. A study of delays along an arterial in Columbia, Mo. showed that 24 out of 30 data sets had delays that were significantly different from those expected from the HCM 2000 delay equations. 29 of the 30 data sets had variances of delay significantly lower than expected if arrivals were random. The results from these studies indicate that delay calculations for signalized intersections in coordinated systems should recognize the effect of signal coordination.

This paper illustrates the field measurements of saturation flow headways and start-up lost times at 11 representative intersections in the state of Maryland. Based on those empirical results, this study has recommended two possible saturation flow rates and a maximum critical lane volume for use in intersection planning analysis that needs to reflect, to the extent possible, the behavior of Maryland’s driving population.

Although traffic circles have been widely used in Turkey for many years, only a few researchers are aware of the advantages of roundabouts. In recent years, few traffic circles were designed as roundabouts in Turkey, but limited study has been made on the capacity and performance analysis of roundabouts. In this study, the applicability of the Highway Capacity Manual 2000 (HCM 2000) procedure for roundabouts in Turkey is discussed. The results show that the HCM 2000 procedure can be an important tool for an initial prediction but further studies should be made in order to develop a more reliable capacity and performance analysis procedure for Turkey.

This paper proposes, for the first time, a new set of level-of-service (LOS) standards for signalized crosswalks in Hong Kong commercial/shopping areas which explicitly take the bi-directional pedestrian flow effects into account. An interview survey technique which utilized pedestrian stated preference was used to determine the respective congestion boundaries for each service level. This paper defines explicitly the LOS boundaries for different levels of bi-directional flow regarding area occupancy, pedestrian flow, and walking speed. The boundaries range from strong effect (0.1–0.5 flow ratios) on the minor flow direction to a mild effect (0.5–1.0 flow ratios) on the major flow direction. These results are complementary to and are in keeping with those LOS standards for walkways reported in previous studies which did not account for the effects of bi-directional flow. The determined perceived pedestrian LOS under bi-directional flow is expected to be directly applicable to Hong Kong or other Asian cities with similar pedestrian physical characteristics and land use.

The present work shows the results of a research study of the operation of the first interurban Chilean freeway [“Autopista del Sol,” $120\mathrm{km}(75\mathrm{mi})$ ]. The results of the study made it possible to obtain the first speed–flow model for a representative segment of a Chilean freeway and compared these results with the Highway Capacity Manual (HCM) 1985 and 2000 models. The study also permitted producing a number of important recommendations for freeway design and operational improvements for Chilean freeways. The results of the work show that the speed–flow model obtained for Autopista del Sol lies between the 1985 and 2000 HCM models. The difference found in the model with respect to those proposed in the manual are discussed.