Panos D Prevedouros

DETAILED OBSERVATIONS OF SATURATION HEADWAYS AND START-UP LOST TIMES

The analyses conducted in this research were based on three methodologies for the field measurement of saturation headways. The first method (M1), the one on which most past studies were based, measured the characteristics of Vehicles 4 to 12 in a standing queue. M2, the method found in the Highway Capacity Manual (HCM), counted all vehicles in a standing queue, regardless of queue length. M3 included arrivals that joined the standing queue as long as vehicles were up to 140 ft from the stop line. This study focused on one approach of a high-design intersection with heavy, random arrivals. The large number of observations and the practically ideal traffic conditions enabled the acquisition of several statistically significant results on saturation flow (s), start-up lost time (SULT), and start-up response time (SRT): (a) when long queues are present, the typical field measurement of s based on the first 12 vehicles is an overestimate of s for through vehicles and an underestimate of s for protected left-turning vehicles; (b) the type of movement had a more dominant role in determining s than the level of saturation (or queue length); (c) SRT displayed a bigger variation than headways— the left-turning movement had a significantly shorter SRT than the through movement did; and (d) much higher SULTs were estimated in this study compared with those in the HCM.

Signal Control for Oversaturated Intersections Using Fuzzy Logic

The fuzzy logic controller (FLC) presented in this paper simulates the control logic of experienced human traffic controllers such as police officers who supersede signal controls at over-saturated intersections during special events. Given real-time traffic information, the FLC controller decides on whether to extend or terminate the current green phase based on a set of fuzzy rules. A microscopic simulator, the Intersection Control Simulator (ICS), was developed to facilitate the evaluation of the proposed FLC strategy. The FLC strategy was compared with pretimed and actuated control strategies using a typical intersection with varying traffic volume levels. Based on delay, speed, % stops, time in queue and throughput-to-demand ratio statistics, the FLC strategy produced significant improvements over pretimed and actuated control strategies under heavy traffic volumes. This indicates that FLC has the potential to improve operations at over-saturated intersections.

Simulation of Large Freeway and Arterial Network with CORSIM, INTEGRATION, and WATSim

Simulation of a large integrated (street and freeway) network with three state-of-the-art software programs is presented. The 20-centerline-km network includes three on-ramps, three off-ramps, an on-and off-ramp weaving section, and a high design arterial with 11 signalized intersections. After considerable modifications to default settings, all three software programs were able to replicate field-measured volumes well. INTEGRATION required extensive modifications to approximate complex signal timing plans and had problems with lane alignment on the wide arterial. CORSIM’s FRESIM component had difficulty with vehicles that miss their destination and required car-following parameter settings corresponding to unusually high capacities to produce good results. WATSim needed the fewest modifications, and it was primarily sensitive to merging and acceleration lengths. WATSim and CORSIM speeds were close to each other. INTEGRATION’s simplified treatment of signalization produced higher street link speeds.

SIGNALIZED INTERSECTION LEVEL OF SERVICE INCORPORATING SAFETY RISK

A methodology that quantifies potential conflicts between left-turning vehicles and opposing through vehicles and pedestrians is presented. The methodology was based on and designed to be compatible with the Highway Capacity Manual 2000. A model was developed to combine delay and safety to get a comprehensive level-of-service indicator, the delay and safety index (DS). A case study of two intersections shows that if potential conflict is not considered, the signal timing plan with permitted left turns delivers a better level of service than that with protected left turns. However, if potential conflict is considered, the level of service under protected left-turn phasing is better than that under permitted left-turn phasing, according to the DS, when the safety weight factors exceed a certain value. The proposed method models the trade-off between safety and efficiency explicitly and considers both vehicle-to-vehicle and vehicle-to-pedestrian conflicts associated with left turns.

Comparison of INTEGRATION, TSIS/CORSIM, and WATSim in replicating volumes and speeds on three small networks

INTEGRATION, TSIS/CORSIM, and WATSim can simulate traffic operations on mixed arterial and freeway networks. Comparisons are presented here using three small networks in Honolulu for which detailed, simultaneous, and contemporaneous flow conditions are known. The models produced reasonable and comparable results on most network links. Of the three software programs, only INTEGRATION can simulate U-turns, but it also is least able to model complex signal operations. TSIS/CORSIM is best at replicating lane-changing behavior, but its percentile input for off-ramps is both inconvenient and inaccurate. WATSim needed the least calibration for producing good results, but its animation is inferior and its capacity-based car-following parameters are undesirable. The default parameters off all three software programs never offered satisfactory results.

ASSOCIATIONS OF PERSONALITY CHARACTERISTICS WITH TRANSPORT BEHAVIOR AND RESIDENCE LOCATION DECISIONS

The objective of this paper is to investigate potential associations between personality and individual travel behavior characteristics. The explorations were based on responses to a mailback household survey from individuals residing in selected Chicago suburbs conducted in spring 1989. Three dimensions of personality were examined: social introversion or extroversion, affinity for suburban living and affinity for material possessions. Personality characteristics tend to correlate well with residence location selection, automobile ownership and travel characteristics. Specifically, socially extroverted people tend to make more trips, more nonwork trips and travel substantially longer distances by automobile for nonwork trips compared with socially introverted people. Materialistic people tend to spend a larger portion of their income for automobile acquisition; they also tend to own more expensive automobiles compared with utilitarian people. More people with an affinity for suburban living tend to reside in outerring, low-density suburbs instead of innerring, high-density suburbs. Thus, personality factors improve the understanding of transport behavior. On the other hand, personality characteristics cannot be affected by policy measures, while values for personality variables are hard to gather and predict. The problem of application of models with personality variables may be solvable for current (i.e. nonforecasting) applications if people can be classified into a small number of personality classes which can be assessed by a manageable number of attitudinal statements. As this study demonstrates, this is feasible.

Urban Freeway Crash Analysis : Geometric, Operational, and Weather Effects on Crash Number and Severity

Associations between the number of crashes and the severity of crashes with a long list of potentially contributing factors, such as geometric and operational characteristics and weather conditions, were investigated. Both aggregate and disaggregate databases with crash statistics were used. Severity was estimated with constants for the different impact (cost) of fatalities, injuries, and material damages. Noteworthy associations included the negative correlation with the speed limit (spots with lower speed limits have more, or more severe, crashes), existence of merge–diverge pavement markings (suggesting the possibility of an illegal driving maneuver), downhill grade sections, and curves. Several temporal variables such as months, days, or time of day with a higher frequency of crashes worked well in models, but those were findings of local interest. An important outcome of this analysis is the absence of any major correlation, which implies that crashes on the modern and mildly congested Attica Tollway in Greece are events largely attributable to driver behavior and other circumstances that cannot be accounted for by geometric, operational, or other temporal variables. Findings of this research suggest that fixed and temporal roadway characteristics and the presence of rain or wet pavements may explain (and likely contribute to) about 5% to 10% of the crashes and severity of crashes observed in 2004 and 2005 on the Attica Tollway. The 2006 report from the 100-Car Naturalistic Driving Study concluded that nearly 80% of all crashes involved driver inattention, lending support to the finding that roadway and environmental factors are relatively minor causes of crashes.

Derivation of Origin-Destination Distributions from Traffic Counts: Implications for Freeway Simulation

Origin-destination (O-D) traffic flows are an essential element in several freeway and network traffic models. In general, it is impossible to identify a unique O-D matrix from volume counts alone. Several methods for deriving O-D data exist, and they vary in complexity, cost, and analysis time. O-D matrices were generated with five methods that were applied to the same set of volume data. The resulting O-D matrices were used as the only variable input component in traffic simulation with INTEGRATION. Traffic simulation output was used to assess the implications of the O-D distribution. The O-D data produced by the deterministic method were clearly different from those of the other four methods. The proportionate and QueensOD (with default seed) output were somewhat dissimilar. All other combinations were similar, and the proportionate and FREQ O-D output were statistically identical. The simulation output with the proportionate-method O-D data met the 10/75 speed criterion at all five of the cross-sectio...

User perceptions of signalised intersection level of service using fuzzy logic

Delay has been selected as the only measure for determining signalised intersection level-of-service (LOS). Previous studies reported that road users consider multiple factors in their evaluation of LOS, including traffic-related and non-traffic factors. The findings from more than 1300 responses to a web-based stated-preference survey suggest that road users consider multiple factors for the evaluation of signalised intersections. A methodology based on fuzzy logic is presented in this article to determine the signalised intersection LOS that explicitly accounts for user perceptions. To reflect the fuzziness of user perceptions, rigid LOS thresholds were replaced with fuzzy numbers. Fuzzy inferences were applied to combine important factors at signalised intersections for deriving a composite LOS measure. A case study with different improvement scenarios was conducted to illustrate the proposed method. Overall, the fuzzy logic method simulates the human reasoning process and provides a feasible alternative to quantify the user perceptions of signalised intersection LOS.

Evaluation of Autoscope, SmartSensor HD, and Infra-Red Traffic Logger for Vehicle Classification

The collection of vehicle classification data, and of heavy goods vehicle or truck data in particular, is fundamental to the design and maintenance of transportation infrastructure. Classification monitoring efforts also improve the availability and reliability of volume data, which are the backbone of traffic analyses and transportation management systems. Nonintrusive sensors minimize the adverse impact on traffic and surrounding communities (e.g., closing traffic, cutting the pavement) when installed and maintained. The application of nonintrusive sensors for vehicle classification is possible for a simplified scheme of classes, and accuracy expectations improve, along with the rapid development of the nonintrusive technology. Three sensors were tested to evaluate the accuracy and reliability of vehicle classification: Autoscope RackVision Terra, a length-based classification sensor utilizing video imaging technology; the Infra-Red Traffic Logger (TIRTL), an axle-based classification sensor utilizing active infrared technology; and SmartSensor HD, a length-based classification sensor utilizing microwave radar technology. The accuracy of traffic sensors for vehicle classification was established with simultaneous field observations (direct or videotaped) or comparison of classification data collected simultaneously by different sensors. The conclusion is that only TIRTL can provide reliable classification under ideal conditions, while Autoscope can be accurate for some simplified classes. The SmartSensor HD did not provide good class counts on the basis of various deployments in Honolulu, Hawaii.