The National Academies Press

Currently Skimming:

Pages 13-94

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 13... ... V-1 SECTION V Description of Strategies Objectives The main goal of the objectives in this guide is the improvement in the safety of signalized intersections and their approaches. Safety improvement measures include geometric design modifications, changes to traffic control devices, enforcement, and education. Read the entire page →
From page 14... ... SECTION V -- DESCRIPTION OF STRATEGIES V-2 • Improve access management near signalized intersections -- Navigation, braking, and decision-making on intersection approaches creates additional workload on the driver. The presence of driveway access at or near a signalized intersection may confuse drivers using the intersection and create additional vehicle-vehicle conflicts. Read the entire page →
From page 15... ... SECTION V -- DESCRIPTION OF STRATEGIES Types of Strategies The strategies in this guide were identified from a number of sources, including recent literature, contact with state and local agencies throughout the United States, and federal programs. Some of the strategies are widely used, while others are used at a state or local level in limited areas. Read the entire page →
From page 16... ... • Proven (P) : Those strategies that have been used in one or more locations and for which properly designed evaluations have been conducted which show them to be effective. Read the entire page →
From page 17... ... SECTION V -- DESCRIPTION OF STRATEGIES Within this guide, PI&E campaigns, where application is deemed appropriate, are usually used in support of some other strategy. In such a case, the description for that strategy will suggest this possibility (in the exhibits, see the attribute area for each strategy entitled "Associated Needs") Read the entire page →
From page 18... ... • Strategies Directed at Improving the Safety Management System: There should be in place a sound organizational structure, as well as infrastructure of laws, policies, etc., to monitor, control, direct, and administer a comprehensive approach to highway safety. It is important that a comprehensive program not be limited to one jurisdiction, such as a state Department of Transportation (DOT) Read the entire page →
From page 19... ... SECTION V -- DESCRIPTION OF STRATEGIES highest-risk movements at signalized intersections. Protected left-turn phases (i.e., the provision for a specific phase for a turning movement) Read the entire page →
From page 20... ... SECTION V -- DESCRIPTION OF STRATEGIES V-8 In terms of explicit concern for safety, protected-only phasing may be the best option. A study by Shebeeb (1995) Read the entire page →
From page 21... ... SECTION V -- DESCRIPTION OF STRATEGIES V-9 EXHIBIT V-2 (Continued) Strategy Attributes for Use of a Protected Left-Turn Signal Phase (P) Read the entire page →
From page 22... ... SECTION V -- DESCRIPTION OF STRATEGIES V-10 EXHIBIT V-2 (Continued) Strategy Attributes for Use of a Protected Left-Turn Signal Phase (P) Read the entire page →
From page 23... ... SECTION V -- DESCRIPTION OF STRATEGIES Use Split Phases Certain geometric configurations, such as left-turn travel paths that overlap with the opposing left-turn path, may require the use of split phasing at an intersection. Split phasing allows opposing movements on the same roadway to proceed through the intersection at different times and is a way to address several geometric situations that pose safety problems for vehicles on opposite approaches (see Exhibit V-3) Read the entire page →
From page 24... ... SECTION V -- DESCRIPTION OF STRATEGIES V-12 EXHIBIT V-4 (Continued) Strategy Attributes for Using Split Phases (T) Read the entire page →
From page 25... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 A2: Optimize Clearance Intervals (P) General Description The clearance interval is the portion of a signal cycle between the end of a green phase and the beginning of the next green phase for a conflicting movement. Read the entire page →
From page 26... ... react to the reassignment of ROW. Longer clearance intervals may also be effective at intersections with significant physical size, to allow drivers to clear the intersection before the opposing traffic enters. Read the entire page →
From page 27... ... SECTION V -- DESCRIPTION OF STRATEGIES V-15 EXHIBIT V-5 (Continued) Strategy Attributes for Optimizing Clearance Intervals (P) Read the entire page →
From page 28... ... Information on Current Knowledge Regarding Agencies or Organizations That Are Implementing This Strategy Agencies are utilizing technology to automatically extend signal intervals in order to aid drivers approaching a signalized intersection in determining whether to stop or proceed through the intersection. The "dilemma zone" for an intersection is a specific road segment, prior to the intersection, in which the driver will be able neither to stop safely before entering the intersection nor to proceed through the intersection without violating the red indication. Read the entire page →
From page 29... ... SECTION V -- DESCRIPTION OF STRATEGIES Crashes related to turning maneuvers include angle, rear-end, pedestrian, and sideswipe (involving opposing left turns) type crashes. Read the entire page →
From page 30... ... SECTION V -- DESCRIPTION OF STRATEGIES V-18 EXHIBIT V-6 (Continued) Strategy Attributes for Prohibiting or Eliminating Turning Movements (Including RTOR) Read the entire page →
From page 31... ... SECTION V -- DESCRIPTION OF STRATEGIES V-19 EXHIBIT V-6 (Continued) Strategy Attributes for Prohibiting or Eliminating Turning Movements (Including RTOR) Read the entire page →
From page 32... ... Strategy 17.2 A4: Employ Signal Coordination (P) General Description Signal coordination has long been recognized as having beneficial effects on the quality of traffic flow along a street or arterial. Read the entire page →
From page 33... ... SECTION V -- DESCRIPTION OF STRATEGIES V-21 EXHIBIT V-7 (Continued) Strategy Attributes for Signal Coordination (P) Read the entire page →
From page 34... ... SECTION V -- DESCRIPTION OF STRATEGIES V-22 EXHIBIT V-7 (Continued) Strategy Attributes for Signal Coordination (P) Read the entire page →
From page 35... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 A5: Employ Emergency Vehicle Preemption (P) General Description Signal preemption allows emergency vehicles to disrupt a normal signal cycle in order to proceed through the intersection more quickly and under safer conditions. Read the entire page →
From page 36... ... SECTION V -- DESCRIPTION OF STRATEGIES V-24 EXHIBIT V-8 (Continued) Strategy Attributes for Employing Emergency Vehicle Signal Preemption (P) Read the entire page →
From page 37... ... SECTION V -- DESCRIPTION OF STRATEGIES Information on Agencies or Organizations Currently Implementing This Strategy The Oregon DOT uses an on-line explanation and form for localities desiring to install signal preemption devices along state highways; see http://www.odot.state.or.us/traffic/ signalpre.htm. Strategy 17.2 A6: Improve Operation of Pedestrian and Bicycle Facilities at Signalized Intersections (Combination of Tried and Proven Strategies) Read the entire page →
From page 38... ... • Public information or signs that educate pedestrians regarding use of push buttons (specifically, that they will not receive the walk signal immediately) , and • Technology to show a push button is working (such as a button that lights up, similar to an elevator) Read the entire page →
From page 39... ... SECTION V -- DESCRIPTION OF STRATEGIES V-27 EXHIBIT V-9 Strategy Attributes for Removing Unwarranted Traffic Signals (P) Attribute Description Technical Attributes Target Expected Effectiveness Keys to Success Potential Difficulties This strategy is targeted at signalized intersections where traffic volumes and safety record do not warrant a traffic signal. Read the entire page →
From page 40... ... SECTION V -- DESCRIPTION OF STRATEGIES V-28 EXHIBIT V-9 (Continued) Strategy Attributes for Removing Unwarranted Traffic Signals (P) Read the entire page →
From page 41... ... SECTION V -- DESCRIPTION OF STRATEGIES Objective 17.2 B -- Reduce Frequency and Severity of Intersection Conflicts through Geometric Improvements Geometric improvements can provide both operational and safety benefits at signalized intersections. Improvements to turning movements, through channelization or even physically preventing turns, can result in reductions in certain types of crashes. Read the entire page →
From page 42... ... Improve Left-Turn Lane Geometry. Safety improvements can also be made to approaches that already incorporate separate left-turn lanes. Read the entire page →
From page 43... ... SECTION V -- DESCRIPTION OF STRATEGIES Delineate Turn Path. Even at signalized intersections, where the traffic signals help to eliminate confusion about ROW, driver confusion can exist in regard to choosing the proper turn path. Read the entire page →
From page 44... ... turning right for which a clear path is not readily apparent. This strategy is also appropriate for application where the roadway alignment may be confusing or unusual, such as a deviation in the path for through vehicles. Read the entire page →
From page 45... ... SECTION V -- DESCRIPTION OF STRATEGIES V-33 EXHIBIT V-12 (Continued) Strategy Attributes for Providing or Improving Left-Turn Channelization (P, T) Read the entire page →
From page 46... ... SECTION V -- DESCRIPTION OF STRATEGIES V-34 EXHIBIT V-12 (Continued) Strategy Attributes for Providing or Improving Left-Turn Channelization (P, T) Read the entire page →
From page 47... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 B2: Provide or Improve Right-Turn Channelization (P) This strategy includes providing right-turn lanes and lengthening right-turn lanes. Read the entire page →
From page 48... ... It is possible that installation of a right-turn lane could create other safety or operational problems at the intersection. For example, vehicles in the right-turn lane may block the cross street right-turning drivers' view of through traffic; this would be a significant issue where RTOR are permitted on the cross street. Read the entire page →
From page 49... ... SECTION V -- DESCRIPTION OF STRATEGIES Where curbed islands are provided, they offer a refuge for pedestrians. Where it is known that channelization islands are being used by pedestrians, crossing paths should be clearly delineated, and the island itself should be made as visible as possible to passing motorists. Read the entire page →
From page 50... ... intersection more safely and more efficiently. Multivehicle crashes (specifically rear-ends) Read the entire page →
From page 51... ... SECTION V -- DESCRIPTION OF STRATEGIES be needed to reduce severe crash rates. There may be multiple problems associated with one or more movements at the intersection that can be best addressed with significant improvements to intersection design. Read the entire page →
From page 52... ... the rear and sides of their vehicle to observe blind spots. They may also have trouble identifying gaps in traffic when making a left turn or safely merging with traffic when making a right turn. Read the entire page →
From page 53... ... SECTION V -- DESCRIPTION OF STRATEGIES Close Intersection Leg. Read the entire page →
From page 54... ... SECTION V -- DESCRIPTION OF STRATEGIES V-42 EXHIBIT V-15 (Continued) Strategy Attributes for Revising Geometry of Complex Intersections -- Closing Access to an Intersection Leg (T) Read the entire page →
From page 55... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 B5: Construct Special Solutions (T) This strategy includes the following: • Providing indirect left turn, • Reconstructing intersections, converting intersections to roundabouts, • Convert two-way streets to a one-way pair, and • Constructing interchanges. Read the entire page →
From page 56... ... accommodate left-turn lanes and on approaches without enough room for a turn lane long enough to provide sufficient storage capacity. In some cases, it is possible to implement indirect left turns using appropriate signing. Read the entire page →
From page 57... ... SECTION V -- DESCRIPTION OF STRATEGIES V-45 EXHIBIT V-19 Quadrant Roadway Intersection Source: Federal Highway Administration, in press. Read the entire page →
From page 58... ... SECTION V -- DESCRIPTION OF STRATEGIES V-46 EXHIBIT V-20 Split Intersection Source: Federal Highway Administration, in press. Read the entire page →
From page 59... ... SECTION V -- DESCRIPTION OF STRATEGIES Convert to Roundabout. A roundabout can potentially have a better crash experience than a conventional signalized intersection. Read the entire page →
From page 60... ... The safety performance of roundabouts in the United States is not well documented due to the small number that have been built here. A current NCHRP study (Project 3-65) Read the entire page →
From page 61... ... SECTION V -- DESCRIPTION OF STRATEGIES • Allowing pedestrians to only have to deal with traffic from one direction, reducing conflicts with vehicles, and • Providing more gaps for vehicles and pedestrians at unsignalized crossings. The ITE Traffic Safety Toolbox (Institute of Transportation Engineers, 1999b) Read the entire page →
From page 62... ... Objective 17.2 C -- Improve Sight Distance at Signalized Intersections Adequate intersection sight distance contributes to the safety of the intersection. In general, sight distance is needed at signalized intersections for the first vehicle stopped at an approach to be able to see the first vehicles stopped at the other approaches, for drivers making permitted left turns, and for right-turning vehicles. Read the entire page →
From page 63... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 C2: Redesign Intersection Approaches (P) General Description Signalized intersections with sight-distance-related safety problems that cannot be addressed with less expensive methods (such as clearing sight triangles, adjusting signal phasing, or prohibiting turning movements) Read the entire page →
From page 64... ... These crashes are generally rear-end or angle collisions. The ability of approaching drivers to perceive signalized intersections immediately downstream can be enhanced by signing, delineation, and warning devices. Read the entire page →
From page 65... ... SECTION V -- DESCRIPTION OF STRATEGIES Providing a break in pavement markings at intersections also helps to alert drivers to their presence. This includes centerlines, lane lines, and edge lines. Read the entire page →
From page 66... ... Install Rumble Strips on Approaches. Rumble strips can be installed in the roadway on intersection approaches transverse to the direction of travel to call attention to the presence of the intersection and the traffic control used. Read the entire page →
From page 67... ... SECTION V -- DESCRIPTION OF STRATEGIES In addition to potentially restricting driver sight lines, large numbers of appurtenances and signage not associated with the driving task in the vicinity of an intersection can impose a high workload. This may ultimately distract the driver from the task at hand (i.e. Read the entire page →
From page 68... ... SECTION V -- DESCRIPTION OF STRATEGIES V-56 EXHIBIT V-25 Strategy Attributes for Improving Visibility of Signals and Signs at Intersections Attribute Description Technical Attributes Target Expected Effectiveness Keys to Success Potential Difficulties Appropriate Measures and Data Associated Needs Organizational and Institutional Attributes Organizational, Institutional, and Policy Issues Issues Affecting Implementation Time This strategy is targeted at crashes that occur because drivers are unable to see traffic signals and signs sufficiently in advance to safely negotiate the intersection being approached. Crash types would include angle and rear-end crashes. Read the entire page →
From page 69... ... SECTION V -- DESCRIPTION OF STRATEGIES Objective 17.2 E -- Improve Driver Compliance with Traffic Control Devices Safety problems at signalized intersections cannot always be solved only with engineering countermeasures. Enforcement of traffic regulations or public information campaigns may be the best way to improve intersection safety. Read the entire page →
From page 70... ... SECTION V -- DESCRIPTION OF STRATEGIES V-58 EXHIBIT V-26 Strategy Attributes for Providing Public Information and Education (T) Attribute Description Technical Attributes Target Expected Effectiveness Keys to Success Potential Difficulties Appropriate Measures and Data Associated Needs Organizational and Institutional Attributes Organizational, Institutional, and Policy Issues The target for this strategy is crashes related to drivers either being unaware of, or refusing to obey, traffic laws and regulations that impact traffic safety. Read the entire page →
From page 71... ... SECTION V -- DESCRIPTION OF STRATEGIES Strategy 17.2 E2: Provide Targeted Conventional Enforcement of Traffic Laws (T) General Description Enforcement is a potential countermeasure to unsafe and illegal motorist behavior at intersections. Read the entire page →
From page 72... ... has often been found to be short-lived. It is difficult -- if not impossible -- to provide constant enforcement of traffic regulations due to funding and staffing reasons, so periodic enforcement may be necessary to sustain the effectiveness of this strategy. Read the entire page →
From page 73... ... SECTION V -- DESCRIPTION OF STRATEGIES violation, such as date, time, speed of vehicle, and the time that had elapsed since the signal turned red, are printed on the photograph. Police officers review the photos to determine if a violation occurred, and if so, a citation is mailed to either the driver or the vehicle owner, depending on the legislation for the jurisdiction. Read the entire page →
From page 74... ... Canadian Mounted Police Web site for Strathcona County (http://www. strathconacountyrcmp.ca/redlightcam.htm) Read the entire page →
From page 75... ... SECTION V -- DESCRIPTION OF STRATEGIES V-63 EXHIBIT V-28 (Continued) Strategy Attributes for Providing Automated Enforcement of Red-Light-Running (Cameras) Read the entire page →
From page 76... ... SECTION V -- DESCRIPTION OF STRATEGIES V-64 EXHIBIT V-28 (Continued) Strategy Attributes for Providing Automated Enforcement of Red-Light-Running (Cameras) Read the entire page →
From page 77... ... SECTION V -- DESCRIPTION OF STRATEGIES Information on Current Knowledge Regarding Agencies or Organizations That Are Implementing This Strategy See Appendix 8 for a description of a red-light camera program in Howard County, Maryland. Charlotte, North Carolina, has had a red-light running program in operation since 1998. Read the entire page →
From page 78... ... Strategy 17.2 E4: Implement Automated Enforcement of Approach Speeds (Cameras) Read the entire page →
From page 79... ... SECTION V -- DESCRIPTION OF STRATEGIES V-67 EXHIBIT V-29 (Continued) Strategy Attributes for Implementing Automated Enforcement of Approach Speeds (Cameras) Read the entire page →
From page 80... ... SECTION V -- DESCRIPTION OF STRATEGIES V-68 EXHIBIT V-29 (Continued) Strategy Attributes for Implementing Automated Enforcement of Approach Speeds (Cameras) Read the entire page →
From page 81... ... SECTION V -- DESCRIPTION OF STRATEGIES Information on Current Knowledge Regarding Agencies or Organizations That Are Implementing This Strategy Portland and Beaverton, Oregon have jointly published an excellent report on the Internet regarding their experience with photo radar. Although this was not focused upon intersection approaches, it should provide insights that are equally applicable thereto. Read the entire page →
From page 82... ... A description of the program in Boulder, Colorado, may be found at: http://www.ci. boulder.co.us/publicworks/depts/transportation/safety/photoradar.html. Read the entire page →
From page 83... ... SECTION V -- DESCRIPTION OF STRATEGIES Objective 17.2 F -- Improve Access Management near Signalized Intersections Effective access management is a key to improving safety at, and adjacent to, intersections. The number of access points, coupled with the speed differential between vehicles traveling along the roadway and vehicles using driveways, contributes to rear-end crashes. Read the entire page →
From page 84... ... SECTION V -- DESCRIPTION OF STRATEGIES V-72 EXHIBIT V-30 Strategy Attributes for Restricting Cross-Median Access near Intersections (T) Attribute Description Technical Attributes Target Expected Effectiveness Keys to Success Potential Difficulties Appropriate Measures and Data Associated Needs The target of this strategy is crashes involving drivers making turns across medians on approaches to signalized intersections. Read the entire page →
From page 85... ... SECTION V -- DESCRIPTION OF STRATEGIES V-73 EXHIBIT V-30 (Continued) Strategy Attributes for Restricting Cross-Median Access near Intersections (T) Read the entire page →
From page 86... ... A number of major efforts have produced useful guidance documents on access management. The Transportation Research Board Committee on Access Management (ADA70) Read the entire page →
From page 87... ... SECTION V -- DESCRIPTION OF STRATEGIES V-75 EXHIBIT V-31 (Continued) Strategy Attributes for Improving Drainage in Intersection and on Approaches (T) Read the entire page →
From page 88... ... Strategy 17.2 G2: Provide Skid Resistance in Intersection and on Approaches (T) Slippery pavement should be addressed to reduce the potential for skidding. Read the entire page →
From page 89... ... SECTION V -- DESCRIPTION OF STRATEGIES V-77 EXHIBIT V-32 Strategy Attributes for Coordinating Closely Spaced Signals near at-Grade Railroad Crossings (T) Attribute Description Technical Attributes Target Expected Effectiveness Keys to Success Potential Difficulties Appropriate Measures and Data This strategy targets crashes related to queues on approaches to signalized intersections in close proximity to at-grade railroad crossings. Read the entire page →
From page 90... ... Strategy 17.2 G4: Relocate Signal Hardware out of Clear Zone (T) General Description Traffic signal hardware represents a potential roadside hazard similar to utility poles, trees, and other large fixed objects. Read the entire page →
From page 91... ... SECTION V -- DESCRIPTION OF STRATEGIES V-79 Post-mounted signals in the median of a road are often deemed appropriate to reinforce the information presented by the overhead signal heads at the intersection, especially at left-turn lanes, but they are a hazard in that location. However, their benefit may outweigh the disadvantage of the location of the post in the median. Read the entire page →
From page 92... ... Strategy 17.2 G5: Restrict or Eliminate Parking on Intersection Approaches (P) General Description Parking adjacent to turning and/or through lanes on intersection approaches may create a hazard. Read the entire page →
From page 93... ... SECTION V -- DESCRIPTION OF STRATEGIES V-81 EXHIBIT V-34 (Continued) Strategy Attributes for Restricting or Eliminating Parking on Approaches (P) Read the entire page →
From page 94... ... SECTION V -- DESCRIPTION OF STRATEGIES V-82 EXHIBIT V-34 (Continued) Strategy Attributes for Restricting or Eliminating Parking on Approaches (P) Read the entire page →

From page 13...

... V-1 SECTION V Description of Strategies Objectives The main goal of the objectives in this guide is the improvement in the safety of signalized intersections and their approaches. Safety improvement measures include geometric design modifications, changes to traffic control devices, enforcement, and education.