Herbert S Levinson

Freight Generation, Freight Trip Generation, and Perils of Using Constant Trip Rates

Several findings call into question current practices. The chief conclusion is that the accuracy of freight generation (FG) and freight trip generation (FTG) models depends on the consistency between the models structure and actual FG-FTG patterns, the degree of internal heterogeneity of the economic and land use aggregation used to estimate the model, and the appropriateness of the spatial aggregation procedure used to obtain the desired FG-FTG estimates. Relative to model structure, the paper establishes strong reasons to treat FG and FTG as separate concepts, because the latter is the output of logistic decisions, whereas the former is determined by the economics of production and consumption. The connection between business size variables–for example, employment–and FG is relatively strong because they are economic input factors, whereas the one with FTG is weaker because inventory and transportation costs come into play. Thus it is generally not correct to assume proportionality between FTG and business size or to assume that using constant FTG rates could be problematic. For instance, only 18% of the industry sectors in New York City exhibit constant FTG rates per employee. For economic and land use aggregation, the finer the level of detail the better, as independent variables have a better chance to explain FG-FTG. In the case of spatial aggregation, the correct aggregation procedure depends on the underlying disaggregate model. For a FG-FTG model to work well, both economic and land use and spatial aggregations must be appropriate.

Bus Rapid Transit: Synthesis of Case Studies

Bus rapid transit systems have grown in popularity in recent years. Spurred by federal initiatives, the spiraling cost of rail transit, and market realities, a growing number of cities have installed or are planning bus rapid transit (BRT). There is a synthesis of current experience, drawing on ongoing research conducted in a project for TCRP. The nature of BRT is described; where it operates; key features, such as running ways, stations, vehicles, intelligent transportation systems, and service patterns; performance in ridership, travel times, and land development; and the emerging implications for new systems. It is important to match transit markets to rights-of-way; achieve benefits in speed, reliability, and identity; minimize adverse impacts to street traffic, property access, and pedestrians; and obtain community support throughout an open planning process.

BUS RAPID TRANSIT. VOLUME 2: IMPLEMENTATION GUIDELINES

This report, which is published as a two-volume set, identifies the potential range of bus rapid transit (BRT) applications through 26 case studies and provides planning and implementation guidelines for BRT. This report will be useful to policy-makers, chief executive officers, senior managers, and planners. This volume, Volume 2, covers the main components of BRT and describes BRT concepts, planning considerations, key issues, the system development process, desirable conditions for BRT, and general planning principles. It also provides an overview of system types and elements, including stations, vehicles, services, fare collection, running ways, and intelligent transportation system applications. Volume 1 provides information on the potential range of BRT applications, covering planning and implementation background and system description, including operations and physical elements.

MEASURING AND ESTIMATING CONGESTION USING TRAVEL TIME-BASED PROCEDURES

Procedures are presented for measuring and estimating roadway congestion levels. An assessment of users, uses, and audiences indicates a need for congestion measures that are understood by nontechnical audiences, yet are rigorous enough for technical analyses. Travel time-based measurements are deemed most useful for this wide range of needs. Data collected for an NCHRP project were used to identify the number of travel time observations and roadway segments required for reliable estimates of congestion through direct data collection. The data and previous congestion studies were used to develop surrogate procedures that can estimate congestion statistics with readily available traffic count and roadway inventory data. The surrogate estimation procedures were developed to assist agencies when direct data collection is not practical or feasible. Both of these processes—direct measurement and estimation of travel time-related quantities—are important for quantifying congestion.

Transferability of Freight Trip Generation Models

The main objectives of this paper are to assess and define ways to enhance the transferability of freight trip generation (FTG) models. After the key premises that should guide the development of FTG models have been presented, the paper assesses transferability in two ways. The first is through analyses of how well representative FTG models are able to estimate the actual FTG for a number of external validation cases. The second is through FTG econometric models that assess the statistical significance of binary variables that represent specific geographic locations. In addition, the paper introduces and assesses the accuracy of a synthetic correction procedure that is intended to improve the transfer-ability and quality of the estimates provided by the FTG rates available in the literature. The results show that the models developed as part of the National Cooperative Freight Research Programs Project 25, Freight Trip Generation and Land Use, have better prediction capabilities than the models included in other compilations. In addition, the synthetic correction procedures improve transferability, and no locational effects are present in the test data.

Bus Lane Capacity Revisited

Bus use of urban roadways and past bus-capacity experience are reviewed. Field studies and bus simulation analyses were used to validate, update, and extend existing bus stop and berth capacity procedures. A 60-percent coefficient of dwell time variation was used to obtain new estimates of likely failure, and the maximum achievable capacity was based on a 25-percent failure rate. Capacity adjustment factors for skip-stop operation and right turns are derived. Service planning implications are identified. Bus lane capacities depend on how frequently the stops are placed, how long the buses dwell at each stop, traffic conditions and control systems along the bus lane or route, and whether buses can pass and overtake each other. Keeping dwell times and dwell-time variations to a minimum, providing multiple berth stops, and establishing skip-stop patterns will increase the bus and passenger capacity of bus lanes.

Bus Rapid Transit Plans in New York's Capital District

The Capital District Transportation Authority (CDTA) is seeking to implement Bus Rapid Transit (BRT) service in the New York (NY) 5 corridor, which runs for 16.5 mi between Albany and Schenectady. The benefits of BRT will be to improve service for current riders, draw new riders to the system, help spur economic revitalization in the corridor, provide key nodes for new development, and improve the image of transit in the Capital District as a whole. When fully in place, the key features of BRT on NY 5 will include limited-stop service, substantial passenger facilities and amenities at each station, real-time passenger information, improved pedestrian environment, park-and-ride opportunities, priority treatment at intersections, queue jumpers at key points, off-vehicle fare collection, and a specific brand image to distinguish BRT from other bus services. The cumulative impact of these types of improvements—in travel time, passenger comfort, passenger information, and image—will lead to an increase in transit ridership in the NY 5 corridor. Based on experience at other North American transit agencies that have implemented BRT, an increase of 22% to 29% is expected, depending on the ultimate travel time savings that is achieved.

Vehicle Selection for BRT: Issues and Options

Bus Rapid Transit (BRT) is a flexible, high performance rapid transit mode that combines facilities, equipment, service and intelligent transportation systems (ITS) elements into a permanently integrated system with a quality image and unique identity. Vehicles are an extremely important component of BRT systems, because they not only contribute significantly to BRTs image and identity, but also play a strong role in achieving measurable performance success. Vehicle related planning and design issues confront BRT planners in these seven basic areas: capacity, external dimensions; internal layout; doors; floor height; propulsion systems; vehicle guidance; and aesthetics, identity and branding. This paper draws heavily on 26 case studies documented in TCRP Project A-23. It also reflects experience from newer BRT systems and concludes with a series of general principles and guidelines for vehicle design, selection, and use in BRT applications.

New Methodology for Intersection Signal Timing Optimization to Simultaneously Minimize Vehicle and Pedestrian Delays

This study introduces a new methodology for signal timing optimization that is carried out by adjusting green splits of a.m. peak, p.m. peak, and rest of the day timing plans for each signalized intersection in the urban street network without changing the existing cycle length and signal coordination to minimize total vehicle and pedestrian delays per cycle. It contains a basic model that handles vehicle delays only and an enhanced model that simultaneously addresses vehicle and pedestrian delays using two different pedestrian delay estimation methods. Both models are incorporated into a high fidelity simulation-based regional travel demand forecasting model for detailed traffic assignments. A computational study is performed for methodology application using data on Chicago metropolitan area travel demand, traffic counts, geometric designs, and signal timing plans for major intersections in the Chicago central business district (CBD) area. A sensitivity analysis is conducted in the application of the enhanced model to examine the impacts of assigning different weights to vehicle and pedestrian delays on intersection vehicle travel time and delay reductions after signal timing optimization. The computational experiment reveals that after systemwide signal timing optimization, vehicle delays in the CBD area could reduce by 13% when considering only vehicle delays and by 5% when simultaneously considering vehicle and pedestrian delays.

Impact of Traffic Congestion on Bus Travel Time in Northern New Jersey

Traffic congestion in Northern New Jersey imposes a substantial time operational penalty on bus service. The purpose of a project was to quantify the additional travel time that buses need because of traffic congestion. A regression model was developed to estimate the travel time rate (in minutes per mile) of a bus as a function of car traffic time rate, number of passengers boarding per mile, and the number of bus stops per mile. The model was used to estimate the bus travel time rate if cars were traveling under free-flow conditions, and the results were compared with the observed bus travel times.