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45 C H A P T E R 5 : C O N C L U S I O N S A N D S U G G E S T E D R E S E A R C H Conclusions and Suggested Research Introduction This chapter describes the conclusions and suggested research to be undertaken at a future time. The first section summarizes the important findings and the conclusions reached during the course of the project. The second section describes some specific areas where further research would be valuable. Conclusions The roadway system must accommodate many types of usersâbicycles, passenger cars, pedestrians, transit, and trucks. Increasingly, stakeholders are recognizing that there should be an appropriate balance among the various modes from a design, operations, and safety standpoint. Access connections to the roadway are a part of the system. There is increasing recognition that the location and design of access to and from roadways impacts all transportation modes. Studies have shown that effective access management (AM) techniques reduce and manage conflict points along roadways, leading to reductions in delays and crashes. However, there is limited understanding of the effects of AM techniques on multimodal operations, and vice versa, particularly techniques that are implemented in combination. This research project has assembled information from a variety of sources that describe the effects of various AM techniques on the safety and operation of pedestrians, bicycles, transit vehicles, and trucks. Information about the safety and operational effects of several techniques has been extracted from the literature. Information about the safety and operational effects of two techniques has been developed in this project. All of this information has been assembled in the Guide for the Analysis of Multimodal Corridor Access Management (Guide) which is a standalone document that was prepared during the project to facilitate the implementation of project results. The Guide documents the known operational and safety relationships between access management techniques and the automobile, pedestrian, bicycle, public transit, and truck modes. The Guide consolidates the 74 access management techniques into 19 groups of related techniques (e.g., non- traversable medians, frontage and service roads), and is unique in its parallel treatment of five travel modes. In the end, the Guide represents a first-of-its-kind resource document to support multimodal evaluation and complete-streets design. Conclusions Reached from the Practitioner Survey The researchers surveyed practitioners and researchers from various agencies and institutions in the U.S. The survey was used to identify the AM techniques typically used by agencies. It was also used to gather the respondentâs opinion on the effect of various AM techniques on the safety or operation of the non-auto travel modes. Finally, the survey was used to identify agency needs and priorities for information describing the effect of specific AM techniques on the safety or operation of the non-auto modes. A total of 381 individuals responded to the survey.
46 The top AM techniques identified as needing additional analysis (with regard to their interaction with the safety and/or operational performance of non-auto modes) across all respondents are identified in the following list: ï· Manage spacing of traffic signals; ï· Install non-traversable medians; ï· Manage the location and spacing of unsignalized access; and ï· Install roundabout. Conclusions Reached from the Development of Performance Relationships A review of the literature indicates that there are 74 AM techniques that have been used by agencies in the U.S. Information describing the influence of these techniques on the safety or operation of pedestrians, bicycles, transit vehicles, or trucks is very limited. Especially limited is information that can be used to quantify the safety or operational effect of a technique on one or more of these travel modes. This project developed performance relationships to facilitate the evaluation of the following AM techniques: ï· Install right-turn deceleration lane, ï· Install non-traversable median (NTM) on undivided highway, ï· Replace two-way left-turn lane (TWLTL) with non-traversable median, and ï· Install continuous two-way left-turn lane on undivided highway. Right-Turn Deceleration Lane To facilitate the evaluation of the Install right-turn deceleration lane technique identified in the previous bullet list, performance relationships were developed for the following travel modes and performance measure combinations: ï· Model to predict bicycle delay ï· Model to predict transit vehicle delay ï· Model to predict truck delay ï· Model to predict transit vehicle conflict frequency ï· Model to predict truck conflict frequency The installation of a right-turn deceleration lane at a signalized intersection was found to decrease the delay to bicycles, local transit vehicles, and trucks. This trend likely reflects the benefit of separating the right-turning vehicles from the through-traffic lane. If a right-turn deceleration lane is present, a longer lane length was found to reduce the delay to transit vehicles and trucks. The installation of a right-turn deceleration lane at a signalized intersection was found to increase the conflict frequency for local transit vehicles. This trend relates to the increased difficulty that a local bus has returning to the through lanes after pulling into the right-turn lane to pick up passengers. The frequency of transit- and truck-related conflicts was found to increase with an increase in the bus stop frequency (in stops per hour). Transit- and truck-related conflicts were found to decrease with an increase in right-turn deceleration lane length.
47 Two-Way Left-Turn Lane and Non-Traversable Median To facilitate the evaluation of the three techniques associated with median type, performance relationships were developed for the following median-type, travel mode, and performance measure combinations: ï· For streets with a TWLTL: o Model to predict bicycle speed o Model to predict truck speed o Model to predict transit crash frequency o Model to predict truck crash frequency ï· For streets with a NTM: o Model to predict bicycle speed o Model to predict truck speed o Model to predict transit crash frequency o Model to predict truck crash frequency These models predict the safety or operational performance of the specified travel mode as a function of street segment design elements, traffic characteristics, or signal control settings. Two equations (one for NTM and one for TWLTL) for a common mode can be used to separately predict the performance of each median type. Then, the results can be compared to determine which median type provides the best performance for the subject travel mode. The predictive models indicate that bicycle speed tends to be slightly higher on a street with a NTM, relative to a street with a TWLTL, all other factors being the same. Similarly, truck speed tends to be higher on a street with a NTM, all other factors being the same. The predictive models indicate that transit-related crash frequency is smaller for a street with a TWLTL, relative to a street with a NTM, all other factors being the same. A similar trend was found for truck-related crash frequency. This trend is likely due to the increase in total pavement surface width provided by the TWLTL. The TWLTL can be used by drivers to provide greater separation between the transit vehicle and the vehicles in adjacent lanes. With a TWLTL, drivers in an inside lane that desire to pass a transit vehicle in the outside lane can shift closer to the far edge line (perhaps even encroach on the center turn lane) to avoid a possible sideswipe collision. Conclusions Reached on the Guide for the Analysis of Multimodal Corridor Access Management The Guide for the Analysis of Multimodal Corridor Access Management (Guide) produced by this project documents the known operational and safety relationships between access management techniques and the automobile, pedestrian, bicycle, public transit, and truck modes. The Guide consolidates the 74 access management techniques into 19 groups of related techniques (e.g., non-traversable medians, frontage and service roads). The Guide is unique in its parallel treatment of five travel modes. It consolidates the body of knowledge on the safety and operation effects of each technique on each travel mode. It can be effectively used to inform the selection of alternative AM techniques based on consideration of the safety and operation of all affected travel modes. The Guide represents a first-of-its-kind resource document to support multimodal evaluation and complete-streets design.
48 Suggested Research A list of 74 AM techniques was identified for this research project. A review of the literature on each technique was conducted to determine the extent to which quantitative information was available that described the effect of the technique on the safety and operation of the pedestrian, bicycle, transit, and truck travel modes. The findings from this review are identified in Table 3 (in Chapter 3). These findings indicate that information is needed for one or more travel modes for most techniques. It is believed that the information in this table can be used to guide the development of future research needs statements. The 74 techniques were evaluated on the basis of both âneedâ within the engineering profession and development cost. The 20 highest priority techniques are identified in Table 20. The techniques that were explicitly addressed in this project are identified by strikeout text. It is recommended that research be undertaken to develop multimodal performance relationships for the remaining 17 techniques listed in the table. For each technique, an initial study design has been developed and documented in Appendix A. These initial study designs should be consulted when developing research needs statements. Table 20. Techniques identified as candidates for future research. Category Technique (listed by ID code) Primary techniques identified in NCHRP Report 420 1a. Establish traffic signal spacing criteria (A-1-3) 1b. Establish spacing for unsignalized access (A-1-4) 1c. Establish corner clearance criteria (A-1-5) 2a.& 2b. Install non-traversable median on undivided highway and replace TWLTL with non-traversable median (B-3-2, B-3-3, & B-3-4) 2c. Close existing median openings (B-3-5) 2d. Replace full median opening with median designed for left turns from the major roadway (B-3-6) 3c. Install continuous two-way left-turn lane on undivided highway (B-3-11) 3d. Install U-turns as an alternative to direct left turns (B-3-18) 4a. Install right-turn deceleration lane (B-4-3) 4b. Install continuous right-turn lane 5a. Consolidate driveways (B-5-1-1) 5b. Channelize driveways to discourage or prohibit left turns on undivided highways (B-7-3) 6b. Locate/relocate the intersection of a parallel frontage road and a crossroad farther from the arterialâcrossroad intersection (B-2-4) Selected from other techniques identified in NCHRP Report 420 B-3-1 Install median barrier with no direct left-turn ingress or egress. B-4-6 Move sidewalk-driveway crossing laterally away from highway. B-5-2-2 Require access on collector street (when available) in lieu of additional driveway on highway. B-5-2-3 Relocate or reorient access. B-6-8 Replace curb parking with off-street parking. B-6-10 Install Roundabout. B-7-11 Improve driveway sight distance and B-7-12 Regulate minimum sight distance Note: Technique ID codes are referenced to NCHRP Report 420 (Gluck et al., 1999). Techniques identified by strikeout text have been addressed in this project.
49 Finally, it is noted in Chapter 1 (in the section titled Direct Effect of a Technique) that the research conducted to date has focused on quantifying the âdirectâ effect of the AM technique (i.e., the effect when a specific technique is implemented in isolation of other techniques). Very little research has been conducted to quantify how the direct effect may be altered when a second or third technique is also implemented at the same time. Future research on a specific AM technique should consider an expanded scope that includes the study of the subject technique in isolation as well as in combination with other techniques that are often implemented with the subject technique. References Gluck, J., H. Levinson, and V. Stover. (1999). NCHRP Report 420: Impacts of Access Management Techniques. TRB, National Research Council, Washington, D.C.