The popularity of bicycles in North America is growing. As the popularity of bicycles has increased, so has the physical network of separate bicycle facilities and designated bicycle lanes in many locations. As a consequence of this growth, there is a demand for more information about bicycle operations on these facilities. Unfortunately, the state of knowledge regarding bicycle operations in the United States currently lags far behind that of motor vehicles and pedestrians. The international research that has been conducted to date regarding bicycle operations on uninterrupted facilities is thoroughly reviewed, and recommended procedures for the operational analysis of uninterrupted bicycle facilities are outlined. The recommended procedures are based on the concept of “frequencies of events” involving a bicyclist and other bicyclists or facility users. Events are defined as bicycle maneuvers required by a bicyclist on a facility, including passings (same-direction encounters) and meetings (opposite-direction encounters). The frequency of events for an uninterrupted bicycle facility is related to the service volumes of bicycles using or projected to be using the facility and does not have to be observed directly. The proposed procedures are, therefore, recommended based not only on their theoretical substance but also on their ease of use by practitioners.

Roundabouts generally provide safety and other advantages. During peak hours, however, even moderate demands on an upstream approach can result in long delays and driver frustration over downstream movements. A metering signal is one way to ensure that all demands at a roundabout are adequately served. A roundabout metering signal regulates flow into the circle from one approach and thereby creates larger gaps in the circle for downstream entrants. Although metering signals have been used successfully around the world, little guidance is available for U.S. designers. The goal of this research was to provide U.S. designers with some guidance on the use of metering signals. The authors developed a simple macroscopic model based on the Highway Capacity Manual, validated it by using a simulation model, and performed exercises with it on a number of demand combinations to see where a meter might help. The macroscopic model should be helpful as a quick screening tool. The results from application of the model provide evidence that a meter may reduce delays compared with those seen in an unmetered roundabout with some demands. Although signalized intersections produced lower delays than did metered or unmetered roundabouts in most cases tested, roundabouts were sometimes better. Analysts should consider more than just peak period delays in deciding on the optimum traffic control at an intersection. If, with the aid of a metering signal for a few peak hours, a roundabout produces slightly higher delay levels during those peak hours than a standard traffic signal, with consideration of its many other benefits, a roundabout could well be the optimum design.

In Chapter 9 of the 1994 update to the 1985 Highway Capacity Manual, the operational and planning analysis of signalized intersections is discussed. The methodology for saturation flow rate estimation does not consider all elements of the interaction between pedestrians and turning vehicles. This study describes this interaction for left and right turns using a conflict-zone-occupancy approach. A conflict zone is a portion of an intersection, typically in the crosswalk, in which pedestrians and vehicles compete for space. Conflict-zone occupancy, defined as the fraction of the effective green period during which pedestrians occupy a conflict zone, provides the basis for a rational adjustment to saturation flow. This study details the results of a multiregional data collection effort that confirms the validity of the conflict-zone-occupancy approach. In addition, this study describes the effect of geometric constraints, as reflected in the number of receiving lanes versus the number of turning lanes, on turning-vehicle saturation flow. After consideration of signalized intersection phasing and turn protection, one can calculate saturation flow adjustment factors reflecting the effect of pedestrians on lane groups containing vehicles turning left ( fLpb) or right ( fRpb).

Although much is known about the operation of signalized intersections, little or no empirical research has been conducted regarding the effect of bicycles on signalized intersection capacity. The purpose of this study was to accurately quantify the effects of bicycles on signalized intersection capacity through the videotaping of several intersections that had significant bicycle traffic. Through the videotaping of intersections in Davis, California, and Gainesville, Florida, a relationship was determined between bicycle volumes and the percent of the green phase during which bicycle traffic occupies a conflict zone between bicycles and right-turning motor vehicles. It was also determined that one can ascertain the total net occupancy due to pedestrians and bicycles by taking the overlapping effects between bicycles and pedestrians into account. Using this total occupancy due to bicycles and pedestrians, one can calculate a saturation flow adjustment factor ( fRph) that reflects the reduction in saturation flow, and ultimately lane group capacity, for lane groups containing vehicles making permissive right turns in the presence of bicycles and pedestrians. The proposed procedure yields lower saturation flows and capacities than the current Highway Capacity Manual (HCM) procedure. In other words, on the basis of empirical data, when combined with pedestrian effects, the impact of bicycles on the saturation flow of lane groups containing right-turning vehicles is probably more detrimental than previously believed, and the capacities of intersections with significant bicycle and pedestrian traffic may be overestimated by using the current HCM procedures.

The objective of the research described in this paper was to develop the basis for revised operational analysis procedures for transportation facilities with pedestrian users where flow is interrupted by traffic control devices. The paper commences with some background information on pedestrian walking speeds at signalized crossings and on pedestrian noncompliance at these locations. Then both new and revised level-of-service (LOS) tables are provided for analyzing various types of interrupted-flow pedestrian facilities. Results are detailed of a review and synthesis of American and international literature as part of a Federal Highway Administration study of pedestrian and bicycle facilities conducted by North Carolina State University between 1995 and 1998. The year 2000 edition of the U.S. Highway Capacity Manual (HCM) will incorporate, either directly or indirectly, most of the revised and synthesized information described in this paper. The research team recommends that the HCM include some background information that will be helpful for analysts timing signals and performing other operations. The authors of this paper recommend assumed crosswalk walking speeds of 1.2 m/s for most areas and 1.0 m/s for crosswalks serving large numbers of older pedestrians. Another important recommendation was to use delay to pedestrians as the basis for level of service at signalized and unsignalized street crossings. The recommended threshold for LOS F at signalized crossings is 60 s or more of delay per pedestrian, whereas at unsignalized crossings it is 45 s or more of delay per pedestrian.