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12 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Intersection Variable Potential Relationship to Speed Traffic A signalized intersection, a stop-controlled Control/Approach Type intersection, and a yield-controlled intersection require different driver tasks and operating speeds. Wayfinding Complex intersection maneuvers tend to reduce speeds, especially for unfamiliar drivers. Visual Complexity Roadside development, pedestrians, bicyclists, sig- nage, and environmental elements that interest driv- ers may affect speed. Roadside Impedances Roadside parking, bus stops, and vehicle loading zones may interrupt traffic flow near intersections and effect speed reductions. Lane Drops Drivers may slow down to make lane changes. Increased lane densities may also reduce speeds. Merging Through drivers may need to slow down to create gaps for vehicles entering the traffic stream. Sight Distance Drivers may travel at higher speeds through intersec- tions without sight-distance constraints. Sight-dis- tance restrictions can induce a small reduction in speeds, although only for the faster vehicles. Lighting Inadequate lighting may not allow drivers to per- ceive and react in advance of an intersection. Traffic Conditions Congestion, queuing, directional distribution, and low volumes influence speeds through intersections. Exhibit 2-3. Intersection characteristics that may affect intersection speed. 2.5.4 Drivers and Vehicles Different types of drivers will choose different speeds at intersections. Commuters and other familiar drivers may tend to drive faster than infrequent users. Driver age and attitude also influ- ence speed through intersections. Additionally, transit vehicles, heavy vehicles, and recreational vehicles may have especially slow turning speeds, requiring them to travel slower than general traffic to maneuver through an intersection. 2.5.5 Weather Conditions Weather conditions may affect driver behavior and speeds. Drivers may use caution and drive slower during snow, ice, rain, fog, or dust than they do in clear and sunny conditions. 2.6 Conditions Potentially Sensitive to Speed This section identifies a variety of conditions, elements, and data that may indicate that an intersection is particularly sensitive to speed. In some cases, these are contextual considerations

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Speed Considerations 13 related to the intersection configuration, location, or environment; in other cases, the sensitivity might be attributed to specific users or user characteristics at that location. Field conditions may also provide insights into an intersection's sensitivity to speed. This might include observing user behavior or evaluating traffic and safety data. 2.6.1 Common Conditions There are a variety of conditions that may be associated with a heightened sensitivity to speed. Many of these are related to the characteristics that affect speed identified in Exhibit 2-2. If driv- ers are alert to the characteristics of an intersection that make lower speeds desirable, they may slow down. If, however, they are not alert to these characteristics it can create a condition that is sensitive to speed. Examples include the following: Intersections that are difficult to detect--horizontal or vertical curvature of an intersection approach may make it difficult to detect. Intersections within a corridor with a variety of changing contexts (land uses, design philosophies)--drivers need to be warned of the increased need to respond to pedestrians, buses, driveway traffic, or other interruptions in traffic flow. Intersections that link high-order and low-order roadway segments--gateways between rural and urban areas. Intersections with complex geometry or irregular route continuity--requiring a high driver workload to comprehend or navigate through the intersection. Intersections proximate to concentrations of sensitive or high-risk populations--children, elderly, or disabled. An approach with limited sight distance--roadside obstacles, sunlight at certain times of day. Intersections with high-speed differentials or limited acceptable gaps at certain times of day-- long queues for one or more approach lanes. 2.6.2 Observed Field Conditions Field observations of an intersection's operating conditions may provide an opportunity to identify intersections sensitive to speed. 2.6.2.1 Crash Avoidance Patterns Skid marks on a roadway are often an indicator that drivers do not have sufficient time to react to interruptions in the flow of traffic. The direction and location of skid marks may be useful clues for deciphering operating conditions. Skid marks may indicate that drivers are traveling faster than their ability to perceive and react to an intersection condition (i.e., a single, stopped vehicle turning left, a vehicle that is accelerating or decelerating, or the back of a queue that extends beyond the perceived area of the intersection). 2.6.2.2 Driver Behavior Undesirable driver behavior, such as lack of compliance with signals or stop signs, may indi- cate that excessive speeds approaching an intersection do not give drivers enough time to see and react to traffic control. The speeds may be the result of adaptation from the prior segment with drivers unaware of their speed and required stopping distances. Desired speeds might be attained if drivers had assistance in transitioning from one segment to the other. 2.6.2.3 Congestion Patterns Congestion patterns can increase the intersection influence area, creating sensitivity to speed. Congestion patterns that create high-speed differentials (such as those listed in Section 2.4.3), that are associated with increased pedestrian or transit use, or that reduce the availability of acceptable gaps for side street traffic, may indicate a particular sensitivity to speed.