Qualitative and Quantitative Estimation of Pedestrian Level of Service at Signalized Intersections

Pedestrians form the largest single road user group and also are the most vulnerable road users. Pedestrian’s movements are not restricted to lanes or specific routes however they are restricted by the physical boundaries around them such as the presence of walkways or pedestrian ways. The main objective of this study is to identify the various factors affecting pedestrian level of service (PLOS) at signalized intersections and to propose a suitable methodology for estimation of pedestrian level of service. The study carried out to develop a model for pedestrian level of service of signalized intersections in Vijayawada city and Bhubaneswar city based on pedestrian’s perception on safety and comfort. The main factors considered for the development of the model were through traffic, left turning traffic, right turning traffic, number of pedestrians, number of lanes and pedestrian delay. Pedestrian delay was one of the key performance indicators for pedestrian level of service. Total twelve crosswalks from two cities were considered for study purpose. Video graphic method was used for collection of field data. Questionnaire survey was conducted to know the perceived level of service of pedestrians. The various factors required to develop the model extracted from video graphic data. Pearson correlation analysis was done to identify the various significant factors influencing pedestrian level of service. By considering perceived LOS as dependent variable and significant factors as independent variables stepwise regression analysis was done to develop a model which suitable for urban Indian conditions. The study revealed that various factors affecting level of service under heterogeneous traffic condition were turning traffic, through traffic, number of lanes, and number of pedestrian and pedestrian delay

Measuring delays for bicycles at signalized intersections using smartphone GPS tracking data

The article describes an application of global positioning system (GPS) tracking data (floating bike data) for measuring delays for cyclists at signalized intersections. For selected intersections, we used trip data collected by smartphone tracking to calculate the average delay for cyclists by interpolation between GPS locations before and after the intersection. The outcomes were proven to be stable for different strategies in selecting the GPS locations used for calculation, although GPS locations too close to the intersection tended to lead to an underestimation of the delay. Therefore, the sample frequency of the GPS tracking data is an important parameter to ensure that suitable GPS locations are available before and after the intersection. The calculated delays are realistic values, compared to the theoretically expected values, which are often applied because of the lack of observed data. For some of the analyzed intersections, however, the calculated delays lay outside of the expected range, possibly because the statistics assumed a random arrival rate of cyclists. This condition may not be met when, for example, bicycles arrive in platoons because of an upstream intersection. This justifies that GPS-based delays can form a valuable addition to the theoretically expected values

Safety problems in urban cycling mobility. A quantitative risk analysis at urban intersections

The attention to the most vulnerable road users has grown rapidly in recent decades. The experience gained reveals an important number of cyclist fatalities due to road crashes; most of which occur at intersections. In this study, dispersion of trajectories in urban intersections has been considered to identify the whole conflict area and the largest conflict areas between cars and bicycles, and the speeds have been used to calculate exposure time of cyclists and reaction time available to drivers to avoid collision. These data allow the summary approach to the problem, while a risk probability model has been developed to adopt an elementary approach analysis. A quantitative damage model has been proposed to classify each conflict point, and a probabilistic approach has been defined to consider the traffic volume and the elementary unit of exposure. The combination of damage and probability, permitted to assess the risk of crash, at the examined intersection. Three types of urban four-arm intersection, with and without bike paths, were considered. For each scheme, the authors assessed the risk of collision between the cyclist and the vehicle. The obtained results allowed the identification of the most hazardous maneuvers and highlighted that geometry and kinematics of traffic movements cannot be overlooked, when designing an urban road intersection. The strategy proposed by the authors could have a significant impact on the risk management of urban intersections. The obtained results and the proposed hazard estimation methodology could be used to design safer intersections

ESTIMATION METHOD OF LEFT TURN LANE CAPACITY UNDER THE INFLUENCE OF PEDESTRIANS AND CROSSWALK LAYOUT AT SIGNALIZED CROSSWALKS

The left turn lane capacity is highly influenced by the presence of pedestrians under shared signal phasing.  Pedestrian crossing time can be highly influenced by pedestrian platoon maneuver under the influence of traffic signal settings, crosswalk length and bidirectional interactions of pedestrian, due to that left turning vehicles movement may be significantly affected. However, existing capacity estimation methods of left turn lanes did not consider those factors. In addition, the influence of crosswalk layout did not properly consider in the existing methods and researches. This study aims to propose a method to estimate the left turn lane capacity, considering the characteristics of crossing pedestrians and crosswalk layout variations. Waiting pedestrian presence-time is estimated by applying pedestrian presence probability model. In addition, the left turning vehicles discharge flow rate under different crosswalk layout and pedestrian demand condition are investigated and modeled. The left turn lane capacity estimation equation is proposed by characterizing the observed discharge flow rate of left turning vehicles under the influence of crossing pedestrians. It was found that the proposed capacity estimation method can represent the realistic influence of pedestrians and crosswalk layout on the left turn lane capacity at signalized crosswalks

Parametric Estimation of U-Turn Vehicles at Median Openings in Urban Indian Context

The purpose of capacity modelling at U-turns is to develop a relationship between capacity and and its geometric characteristics. In fact, the few models available for the estimation of capacity at different transportation facilities does not provide specific guidelines at median openings. For this reason, an effort is made to estimate the capacity by collecting the data sets from median openings at different lane roads of Hyderabad City, India. Wide difference (43% -59%) among the capacity values estimated by the existing models shows the limitation to consider for the mixed traffic situations. Thus, a new model is proposed for the estimation of the capacity of U-turn vehicles at median openings considering mixed traffic conditions which would further prompt to investigate the effect of different factors that might affect the capacity. In order to estimate the critical gap of U-turn vehicles, recently developed method ‘INAFOGA’ which is based on clearing behavior of drivers at un-signalized intersections is modified and applied considering the merging behaviour of U-turn vehicles at median openings and named as ‘Modified INAFOGA’ method. Modified INAFOGA method is compared with probability equilibrium method through paired-sample hypothesis (t-test) and result revealed that difference in mean values 0.009 signifies that both methods are comparable. Difference in critical gap values obtained from the box plots and radar charts indicates that Probability equilibrium method is not suitable to address the behavior of U-turn vehicles at median openings under mixed traffic conditions and these observations validates the fact that ‘modified INAFOGA’ method is indeed appropriate under mixed traffic conditions. Follow up time is estimated by measuring the time gap between two successive U-turn vehicles which are being queued to take a U-turn. The estimation of capacity model proposed in this paper is simple, easy to implement and suitable to mixed traffic conditions

Signalized Intersection Capacity Adjustment Factors for Makkah, Saudi Arabia

Operation and performance of signalized intersection relies on roadway’s environmental features and users’ behavioral characteristics which significantly differ among locations. Although Highway Capacity Manual (HCM) provides general guide for designing traffic elements, its recommendations regarding particular values of the design parameters may not be universally applicable. This paper analyses saturation flow rate and capacity adjustment factors for signalized intersection in Mecca, Kingdom of Saudi Arabia. The research reveals that the capacity of a signalized intersection in Mecca is 2500 pcphpl which is much higher than the value prescribed in HCM. Capacity adjustments factors also vary from HCM recommendations. Estimated parameters may be useful in signal design and traffic system performance analysis in Saudi Arabia. Moreover, research outputs might be utilized for formulating Highway Capacity Manual for the country

Start-up delay Estimation at Signalized Intersections: Impact of Left-Turn Phasing Sequences

This paper aims to investigate the start-up delay at signalized intersections in Abu Dhabi (AD) city, UAE. Impact of external factors that may affect the start-up delay is examined including left turn phasing sequences (split/lead/lag), movement turning (through/left), intersection location (CBD/non-CBD) and day time (peak/off-peak). A new technique of data collection was applied based on the automate records of license plate of vehicles and a comparison with the traditional video recorded technique was carried out. Data covered 66 approaches of 36 signalized intersections. The analysis showed that overall estimated mean value of the start-up delay is 2.201 sec. with a standard deviation of 1.823 sec. The t-test shows significant statistical difference in start-up delay between observations at through and left movements, at CDB and non-CDB area and at split and lead/lag phasing. However, no significant differences were found between peak and off-peak periods and between split and lead phasing. In general, lead/lag phasing sequences not only improved the overall delay at signalized intersection but also improved the start-up delay.nbsp nbs

Pedestrian perception-based level-of-service model at signalized intersection crosswalks

"jats:p"Pedestrian level of service (PLOS) is an important measure of performance in the analysis of existing pedestrian crosswalk conditions. Many researchers have developed PLOS models based on pedestrian delay, turning vehicle effect, etc., using the conventional regression method. However, these factors may not effectively reflect the pedestrians’ perception of safety while crossing the crosswalk. The conventional regression method has failed to estimate accurate PLOS because of the primary assumption of an arbitrary probability distribution and vagueness in the input data. Moreover, PLOS categories in existing studies are based on rigid threshold values and the boundaries that are not well defined. Therefore, it is an important attempt to develop a PLOS model with respect to pedestrian safety, convenience, and efficiency at signalized intersections. For this purpose, a video-graphic and user perception surveys were conducted at selected nine signalized intersections in Mumbai, India. The data such as pedestrian, traffic, and geometric characteristics were extracted, and significant variables were identified using Pearson correlation analysis. A consistent and statistically calibrated PLOS model was developed using fuzzy linear regression analysis. PLOS was categorized into six levels ("jats:italic"A"/jats:italic"–"jats:italic"F"/jats:italic") based on the predicted user perception score, and threshold values for each level were estimated using the fuzzy "jats:italic"c"/jats:italic"-means clustering technique. The developed PLOS model and threshold values were validated with the field-observed data. Statistical performance tests were conducted and the results provided more accurate and reliable solutions. In conclusion, this study provides a feasible alternative to measure pedestrian perception-based level of service at signalized intersections. The developed PLOS model and threshold values would be useful for planning and designing pedestrian facilities and also in evaluating and improving the existing conditions of pedestrian facilities at signalized intersections. Document type: Articl

17-11 Evaluation of Transit Priority Treatments in Tennessee

Many big cities are progressively implementing transit friendly corridors especially in urban areas where traffic may be increasing at an alarming rate. Over the years, Transit Signal Priority (TSP) has proven to be very effective in creating transit friendly corridors with its ability to improve transit vehicle travel time, serviceability and reliability. TSP as part of Transit Oriented Development (TOD) is associated with great benefits to community liveability including less environmental impacts, reduced traffic congestions, fewer vehicular accidents and shorter travel times among others.This research have therefore analysed the impact of TSP on bus travel times, late bus recovery at bus stop level, delay (on mainline and side street) and Level of Service (LOS) at intersection level on selected corridors and intersections in Nashville Tennessee; to solve the problem of transit vehicle delay as a result of high traffic congestion in Nashville metropolitan areas. This study also developed a flow-delay model to predict delay per vehicle for a lane group under interrupted flow conditions and compared some measure of effectiveness (MOE) before and after TSP. Unconditional green extension and red truncation active priority strategies were developed via Vehicle Actuated Programming (VAP) language which was tied to VISSIM signal controller to execute priority for transit vehicles approaching the traffic signal at 75m away from the stop line. The findings from this study indicated that TSP will recover bus lateness at bus stops 25.21% to 43.1% on the average, improve bus travel time by 5.1% to 10%, increase side street delay by 15.9%, and favour other vehicles using the priority approach by 5.8% and 11.6% in travel time and delay reduction respectively. Findings also indicated that TSP may not affect LOS under low to medium traffic condition but LOS may increase under high traffic condition

Safety and Operational Impacts of Alternative Intersections

As the degradation of service at some conventional intersections increases, there becomes a need for alternative solutions other than expensive interchanges. Many alternative intersections have been proposed in the past. Under certain traffic and local conditions some solutions are more promising than other. In some cases, the conventional intersection may still be the optimal choice. The presented research focused on developing guidelines that would help planners and designers identify the most promising solutions for further analysis. This objective has been addresses in two ways. Firstly, the existing knowledge on alternative intersections has been identified. Secondly, the performance of conventional and alternative intersections under a range of Indiana traffic conditions has been evaluated using micro-simulation model - VISSIM. Although a large number of sources could be found on the research subject, the existing knowledge about performance of alternative intersection design is incomplete. Only a few designs proposed in the past have been applied at a considerable number of locations including roundabouts, median U-turns, and jag-handle intersections. Other types still await implementation. The available sources are not comprehensive and deal with conditions that might be different from Indiana. The knowledge of the safety impact of these intersections is very limited. A large number of more than 1,300 scenarios were simulated runs performed with VISSIM calibrated to Indiana conditions. The simulated types of intersections included: conventional, roundabouts, jag-handle near-sided and far-sided, median U-turns, and continuous-flow intersection. Except roundabouts, all other intersections were signalized to test their capacity limits and delay-based performance. Although the roundabouts were the lowest delays at low volumes they also reached the capacity before other did. The most promising solutions for heavy volumes are median U-turns and continuous-flow intersections. The presented research developed guidelines for using alternative intersection designs. The guidelines compile the existing knowledge found in existing publications and research reports with the simulation experiments performed with VISSIM. The guidelines are ready to use and will help planners and designers determine which intersection types are the most promising under considered conditions and should be considered in a detailed way. The simulation results have been summarized in an easy to use format of graphs