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As the demand for additional capacity on urban freeways continues to increase, there is a need to better understand how to optimize the lane and shoulder configurations so as to improve capacity without adversely impacting operating speed. The overall objective for this research effort was to identify the operational implications of using reduced lane and shoulder widths on freeways. The operational analysis found speeds 3.5 km=h (2.2 mph) higher for a 3.7 m (12 ft) lane as compared to a 3.4 m (11 ft) lane. The authors developed an equation that can be used to predict speeds per lane for freeway locations with boundary conditions similar to those present in the study database. [ABSTRACT FROM AUTHOR]

Freeway interchanges accommodate large traffic volumes within a constrained area. When their design is complex and includes unexpected features, it may increase drivers' workloads and lead to driving errors, thus increasing the likelihood of a crash. The study's goal is to provide a tool for assessing the safety impacts of interchange complexity, promoting a simpler and safer design. This paper presents an interchange complexity model (ICM) that is based on estimations of aggregated drivers' workload in interchanges. A database of 25 interchanges from the New Jersey interstate road system was used to examine the ICM and construct a resulting crash prediction model by comparing their interchange complexity index (ICI) with three years of crash data. Further on, nine additional interchanges were analyzed similarly in order to validate both the use of the ICM and the resulting crash prediction models. Actual observations of the validation data were relatively close to average model predictions. It is proposed that highway planners could use the ICM for estimating the complexity of interchange design alternatives and the implications for road safety to minimize driver errors and thus reduce crash occurrences. [ABSTRACT FROM AUTHOR]

Transportation management policies and practices are currently experiencing evolving trends such as funding limitations, aging facilities, greater travel demand, increased number of visible stakeholders, and higher user expectations. As a result, transportation agencies currently grapple with how to best incorporate a wide range of performance criteria in investment evaluation and decision making. Often, a key prerequisite to multiple criteria decision making is to establish the relative importance of different performance criteria as perceived by decision makers, facility users, and other stakeholders. This paper reviews methods that exist in the literature for weighting and illustrates the applications of some of these methods. For the bridge management case study, the direct-questioning weighting technique was found to yield results that indicated high levels of agreement among bridge experts. For the overall highway asset management case study, the analytical hierarchy process was used to derive the weights across performance criteria. The findings show that the distribution of weights across various highway performance criteria based on the agency perspective can differ from that based on the road users’ perspective. The relative weights of the different performance criteria can help agencies establish the overall combined desirability or otherwise of each alternative transportation action in terms of all performance criteria, identify the best action in a balanced and rational manner, or analyze trade-offs between the alternative actions. [ABSTRACT FROM AUTHOR]

The paper develops a short-term space-time traffic flow forecasting strategy integrating the empirical-based seasonal autoregressive integrated moving average (SARIMA) time-series forecasting technique with the theoretical-based first-order macroscopic traffic flow model—cell transmission model. A case study in Dublin city center which has serious traffic congestion is performed to test the effectiveness of the proposed multivariate traffic forecasting strategy. The results show that the forecasts at the junctions only deviate around 10% at a maximum from the original observations and seem to indicate that the proposed strategy is one of the effective approaches to predict the real-time traffic flow level in a congested network especially at the locations where no continuous data collection takes place. [ABSTRACT FROM AUTHOR]

Capacity can be derived by fitting a relationship between the three fundamental traffic variables: flow, speed, and density. The study uses a dual-regime model with the consideration of all three variables. Different forms of functions were specified for congested and uncongested conditions. An optimization based estimation procedure was developed to minimize the distance between the theoretical functions and the traffic stream variable measurements. The optimal procedure was coded into a computer program and applied to three data sets representing different roadway classifications. The results indicate that the proposed method can produce good estimates of the key traffic stream parameters including the roadway capacity. [ABSTRACT FROM AUTHOR]

Capacity has traditionally been defined deterministically, and has been assumed to occur immediately before breakdown. Recent studies, however, have shown that the value of capacity, i.e., maximum throughput, is probabilistic, and does not always occur immediately before the breakdown. Four different types of flows (i.e., maximum prebreakdown flow, breakdown flow, maximum queue discharge flow, and average queue discharge flow) referred to as “capacity flows” in this paper, are considered to examine how they differ by day of the week and time of the day, and whether they are significantly different by type of freeway segment. Speed and volume data were obtained, which were initially collected by remote traffic microwave sensors at the US-202 southbound near Philadelphia, from May to August 2004. The four types of flows described above were collected and distinguished by time period, day of the week, and segment type. In conclusion, the mean capacity flows were different during different times of the day, but were the same each day of the week. In comparing segment types, capacity flows per lane are generally not equal between merging, diverging, weaving, and lane drop segments. [ABSTRACT FROM AUTHOR]

The goal of this study is to develop a procedure for estimating the capacity of U-turn movement at median openings on multilane highways. Data were collected at six selected median openings in the Tampa Bay area of Florida. The critical gap for U turns was estimated by using the maximum likelihood method. The follow-up time for U turns was determined by using a linear regression model developed in this study. With the estimated critical gaps and follow-up times, Harders model was used to estimate the capacity of U-turn movement. It was found that the median width at median openings greatly impacts the capacity of U-turn movement. Vehicles making U turns at median openings with wide medians (median nose width >=6.4 m) have larger potential capacity than those making U turns at median openings with narrow medians (median nose width <6.4 m). The results of Harders model were tested against the capacity data measured in the field using Kyte’s method. It was found that Harders model provided reasonable capacity estimate for U-turn movement at median openings. [ABSTRACT FROM AUTHOR]

The continuity equation involving traffic flow expresses the relationship between density, flow, and speed. Density equals the flow divided by space mean speed. The formulation of this equation in the year 1952 has two important assumptions. One assumption is that spacing and speed are constant, i.e., uncongested conditions with moderate to slightly high volumes. The other assumption is that homogeneous traffic prevails, vehicle composition is uniform and vehicles behave within strict lane discipline rules. To determine if the continuity equation is valid under nonhomogeneous traffic conditions, one performs an experiment involving data collection of density, flow, and speed at three midblock sites in India. Data collection occurred when uncongested conditions prevailed with moderate to slightly high volumes. Comparing the average density derived from observed densities in the field to the density derived from the continuity equation reveals whether or not the continuity equation accurately predicts average density under nonhomogeneous traffic conditions. Similar traffic operating characteristics served as the basis for grouping vehicles into five traffic entity types. The association between average density based on observed densities of nonhomogeneous traffic and density derived from the continuity equation had a correlation coefficient of +0.88 for light, four-wheeler type, +0.85 for heavy vehicle type, +0.90 for motorized, three-wheeler type, +0.83 for motorized, two-wheeler type, and +0.50 for nonmotorized, two- and three-wheeler type. Additionally, a nonparametric test, i.e., Wilcoxon signed-rank test, compared observed and derived densities. At a 95% confidence level, no significant difference existed between observed and derived densities of light four-wheeler type, heavy vehicle type, motorized two-wheeler type, nonmotorized two- and three-wheeler type, and between cumulative observed and cumulative derived density. Only in the case of the motorized three-wheeler type, the observed, and derived densities are significantly different. These moderate to strong correlations coupled with the results of the nonparametric test validate the application of the continuity equation when traffic is nonhomogeneous. [ABSTRACT FROM AUTHOR]

Weaving areas are one of the major highway facilities that have long been investigated by researchers. Their capacities are currently estimated based on the density 27 pc/km/ln. There is no specific reason why this method can produce accurate estimates. In addition, no data collection has been performed to validate them. This study develops a generalized capacity estimation model for weaving areas, which is applicable to the entire range of configurations of weaving areas, and compares the resulting capacity estimates to field estimates. The proposed methodology is based on gap acceptance theory and linear programming techniques. Speed and flow data over several days were obtained and analyzed to extract the capacity of three study sites along the QE Expressway, Toronto. It was found that, for the three study sites, the proposed methodology provides capacity estimates that are closer to the field-observed capacity values than the Highway Capacity Manual (2000) estimates. [ABSTRACT FROM AUTHOR]

Transportation agencies are becoming more aware of the seriousness of traffic delay caused by urban freeway rehabilitation and are experimenting with the use of intelligent transportation systems to control traffic demand in construction work zones (CWZ). This case study presents the process, evaluation, and public reaction to the implementation of an automated work zone information system (AWIS), as well as an Internet public outreach program, to mitigate traffic delays during the reconstruction of a section of Interstate-15 (I-15) near Devore in Southern California. The project consisted of a 4.5-km stretch of high traffic volume concrete pavement that was rebuilt during two 9-day closures (one for each direction) using continuous construction operations. The approach produced up to 18% reduction in peak-hour traffic demand through the CWZ, which reduced maximum delays from 90 to 50 min producing a $3.6 million benefit in potential road user cost savings. The intelligent systems also contributed to reversing initial public reluctance toward the accelerated rehabilitation approach. The study will help transportation agencies efficiently configure and operate AWIS in combination with public outreach for highway rehabilitation under high traffic volume. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highway maintenance, like rehabilitation or resurfacing, on four-lane, two-way highways usually requires closing one or two lanes to set up a work zone. In this paper we evaluate several alternatives defined by the number of closed lanes, fractions of traffic diverted to alternate routes, and crossover of diverted traffic to opposite lanes. A methodology is developed to minimize the total cost, including agency cost, user cost, and accident cost, by optimizing work zone length for each alternative and finding optimal diversion fraction, while considering the characteristics of the detour route bypassing the work zone. Finally, guidelines for selecting the best alternative for different characteristics of traffic flows, roads, and maintenance processes are developed by deriving thresholds among alternatives. [ABSTRACT FROM AUTHOR]

This paper presents an approach to optimize the short-term traffic prediction performance on freeways using multiple artificial neural network topologies under different network and traffic condition settings. The approach encourages multimodel techniques that are capable of improving the prediction system performance over single-model approaches. Using a mix of neural network topologies, the short-term speed prediction performance was extensively evaluated under different input settings and various prediction horizons (from 5 to 20 min). To enable the networks to learn from historical information, a long-term memory component was introduced to the input patterns to allow the networks to build internal representation of recurrent conditions, in addition to the short-term memory that is encoded in the most recent information. Optimal settings were determined by maximizing the performance under different traffic conditions observed at the target location, as well as upstream and downstream locations. Comparative statistical analysis with naive and heuristic approaches showed that the optimized neural network approach resulted in better prediction performance. The study shows that the optimal settings were consistently more dependent on the long-term memory component as prediction horizon increases. [ABSTRACT FROM AUTHOR]

Recently, a dynamic traffic control system designated as dynamic intersection signal control optimization (DISCO) has been developed. DISCO considers the entire fundamental diagram of traffic flow, which is essential for controlling congested and transient traffic. As a dynamic model, DISCO works with time-variant traffic patterns and derives dynamic timing plans. In this study, we applied DISCO to a congested network in Hong Kong and studied the various control strategies enabled by DISCO. The results showed that DISCO outperformed the existing plans by 30–40% in overall delay reductions. DISCO performed best under the most flexible control scheme of variable-green no-cycle strategy, given a good initial solution for the algorithm. Nevertheless, even good fixed-time plans can produce remarkable results. [ABSTRACT FROM AUTHOR]