Sha A. Mamun

Measuring Service Gaps: Accessibility-Based Transit Need Index

The integration of transit needs into transit accessibility indexing is important for evaluating existing transportation systems and service gaps and for identifying priority areas for investments in transportation infrastructure. This study detailed an indexing model for accessibility of transit need and focused on the necessity of evaluating transit needs and transit accessibility simultaneously. A need index was developed to identify areas in high need of public transit services from economic and sociodemographic information, and a composite accessibility index was developed to identify levels of access to transit services and shortcomings in providing service. The need for transit service was then modeled as the lack of transit accessibility, and the model correlated different access indicators with their ability to predict transit service need. This model mapped areas with different levels of transit accessibility and transit needs by using a single score, which may be easily interpreted by planners who examine transit equity. The model was applied to the city of Meriden, Connecticut, and results were compared with a general approach for consistency and effectiveness. The usefulness of the model was also highlighted through a representative example of the models application.

Safety effects of exclusive and concurrent signal phasing for pedestrian crossing

This paper describes the estimation of pedestrian crash count and vehicle interaction severity prediction models for a sample of signalized intersections in Connecticut with either concurrent or exclusive pedestrian phasing. With concurrent phasing, pedestrians cross at the same time as motor vehicle traffic in the same direction receives a green phase, while with exclusive phasing, pedestrians cross during their own phase when all motor vehicle traffic on all approaches is stopped. Pedestrians crossing at each intersection were observed and classified according to the severity of interactions with motor vehicles. Observation intersections were selected to represent both types of signal phasing while controlling for other physical characteristics. In the nonlinear mixed models for interaction severity, pedestrians crossing on the walk signal at an exclusive signal experienced lower interaction severity compared to those crossing on the green light with concurrent phasing; however, pedestrians crossing on a green light where an exclusive phase was available experienced higher interaction severity. Intersections with concurrent phasing have fewer total pedestrian crashes than those with exclusive phasing but more crashes at higher severity levels. It is recommended that exclusive pedestrian phasing only be used at locations where pedestrians are more likely to comply.

Predicting local road crashes using socioeconomic and land cover data

ABSTRACT Estimating and applying safety performance functions (SPFs), or models for predicting expected crash counts, for roads under local jurisdiction is often challenging due to the lack of vehicle count data to be used for exposure, which is a critical variable in such functions. This article describes estimation of SPFs for local road intersections and segments in Connecticut using socioeconomic and network topological data instead of traffic counts as exposure. SPFs are developed at the traffic analysis zone (TAZ) level, where the TAZs are categorized into six homogeneous clusters based on land-cover intensities and population density. SPFs were estimated for each cluster to predict the number of intersection and segment crashes occurring in each TAZ. The number of intersections and the total local roadway length were also used as exposure in the intersection and segment SPFs, respectively. One aggregate SPF using the entire data set was also estimated to compare with the individual cluster SPFs. Ten percent of the observed data points were reserved for out-of-sample testing, and in all cases these out-of-sample predictions were as good as the in-sample predictions. Models including total population, retail and nonretail employment, and average household income are found to be the best on the basis of model fit and out-of-sample prediction.

A study of pedestrian compliance with traffic signals for exclusive and concurrent phasing

This paper describes a comparison of pedestrian compliance at traffic signals with two types of pedestrian phasing: concurrent, where both pedestrians and vehicular traffic are directed to move in the same directions at the same time, and exclusive, where pedestrians are directed to move during their own dedicated phase while all vehicular traffic is stopped. Exclusive phasing is usually perceived to be safer, especially by senior and disabled advocacy groups, although these safety benefits depend upon pedestrians waiting for the walk signal. This paper investigates whether or not there are differences between pedestrian compliance at signals with exclusive pedestrian phasing and those with concurrent phasing and whether these differences continue to exist when compliance at exclusive phasing signals is evaluated as if they had concurrent phasing. Pedestrian behavior was observed at 42 signalized intersections in central Connecticut with both concurrent and exclusive pedestrian phasing. Binary regression models were estimated to predict pedestrian compliance as a function of the pedestrian phasing type and other intersection characteristics, such as vehicular and pedestrian volume, crossing distance and speed limit. We found that pedestrian compliance is significantly higher at intersections with concurrent pedestrian phasing than at those with exclusive pedestrian phasing, but this difference is not significant when compliance at exclusive phase intersections is evaluated as if it had concurrent phasing. This suggests that pedestrians treat exclusive phase intersections as though they have concurrent phasing, rendering the safety benefits of exclusive pedestrian phasing elusive. No differences were observed for senior or non-senior pedestrians.

Access and Connectivity Trade-Offs in Transit Stop Location

A formulation is proposed to address the trade-off between transit user access and trip connectivity. Transit access is typically regarded as the physical proximity to transit service. Additional stops can provide greater access to the service and reduce walking distance to stops. However, closer stops do not guarantee that routes serving the stops are well connected to desired trip destinations. In general, transit riders are willing to walk longer distances to access a stop that has frequent transit service, requires less wait time, and is well connected to their desired destinations. Frequent stops on the way to these desired destinations, although they provide shorter walking distance for some passengers, increase dwell time; this dwell time results in a smaller portion of the networks being connected within a certain travel time, which is an important element of the connectivity of the system. The proposed methodology considers both the impact of access distance to transit stops and trip connections to destinations for determining optimal stop locations and setting optimal transit line frequencies. The bus stop location model is formulated as a mixed-integer program and the coin-or branch-and-cut solver is used to solve the problem. Sensitivity analyses are performed and computational results are presented for an illustrative example. To illustrate the usefulness of the model, the formulation is applied to the bus transit network in New Haven, Connecticut, as a case study.