Design Guide for Addressing Nonrecurrent Congestion (2014) / Chapter Skim
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Pages 91-135
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From page 91... ...
89 4 CATALOG OF SECONDARY TREATMENTS This chapter presents a catalog of secondary treatments that can be considered for use in addressing nonrecurrent congestion. A detailed summary of each of the secondary treatments is provided that includes the following information: • Description and objective • Typical applications • Design criteria • How treatment reduces nonrecurrent congestion • Factors influencing treatment effectiveness • Cost The secondary treatments are classified based on similarities with respect to function or location on the roadway.
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From page 92... ...
90 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Figure 4.1. Contraflow operations used in South Carolina after a hurricane.
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From page 93... ...
91 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION used differently in an attempt to increase capacity, such as by allowing travel on the shoulder or ignoring lane lines to facilitate an additional, narrower lane on the roadway segment. Finally, consideration should be given to the likelihood of additional traffic demand from nearby jurisdictions that are evacuating through the area being considered.
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From page 94... ...
92 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION o Installation of permanent signs for use during evacuation o Installation of permanent fold-out–type signs • Ongoing costs o Police officers to direct traffic o Implementation of temporary message boards to be used during evacuation o Implementation of gates or barricades o Implementation of temporary or portable signing o Service and maintenance for gates, ITS, and other devices Contraflow Lanes for Work Zones Description and Objective A contraflow lane is a lane that has been "borrowed" from one direction of travel to add capacity to the other direction of travel. Contraflow lanes are most often used when either an increase in demand or decrease in capacity necessitates finding additional capacity to serve vehicles in that direction.
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From page 95... ...
93 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION with striping changes, concrete barriers, or flexible delineators. Additional pavement may be required to route traffic through the median to the contraflow lane.
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From page 96... ...
94 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Traffic can be shifted away from work zones to provide highway workers with more clearance from traffic. The basic disadvantages of the contraflow strategy are as follows: • There is an increased risk of serious head-on collisions when traffic normally separated by a barrier or median is now flowing in adjacent lanes.
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From page 97... ...
95 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Reduces Impact of Work Zone A contraflow lane may be used during a work zone to offset the reduction of available lanes in the direction affected by the work zone. For example, if a work zone is planned that will block two lanes, the contraflow lane may borrow one lane from the opposing direction for the duration of the work zone, thereby offsetting the negative impact of the work zone by 50%.
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From page 98... ...
96 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION By providing additional capacity during a work zone event, contraflow lanes can improve roadway operations by reducing delay and improving reliability. Factors Influencing Treatment Effectiveness Several factors may influence the effectiveness of contraflow lanes at reducing nonrecurrent congestion due to work zones: • The number of lanes to be shifted • Traffic volume in the direction of the proposed contraflow lane • Roadway capacity in the direction of the proposed contraflow lane • Traffic volume in the opposing direction of the proposed contraflow lane • Roadway capacity in the opposing direction of the proposed contraflow lane Contraflow lanes for short-term work zones will be the most cost-effective when volume-to-capacity ratios are high in the direction of the proposed contraflow lane and low in the opposing direction.
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From page 99... ...
97 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION High-occupancy toll (HOT) lanes are similar to HOV lanes, but instead of being exclusively for vehicles with passengers, they are also open to motorists without passengers but who are willing to pay a toll to use them.
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From page 100... ...
98 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Typical Applications HOV–HOT lanes are widely used around the country to encourage carpooling and transit ridership along heavy commuter routes. They are often retrofitted on existing roadway cross sections by using some or all of the shoulder and striping narrower general-purpose lanes.
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From page 101... ...
99 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION three types of facilities (i.e., they are not designed to facilitate vehicles moving back and forth between the general-purpose lanes and the HOV lanes) , they probably have less potential to reduce nonrecurrent congestion.
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From page 102... ...
100 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • Dynamic message board construction and operation costs • Costs of additional staff to monitor roadway conditions and initiate opening of HOV lane to all traffic In some cases, this treatment may be implemented for a negligible cost, particularly along freeways with existing traffic management centers. If infrastructure improvements are needed, costs may range from thousands to tens of thousands of dollars.
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From page 103... ...
101 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Design Criteria When evaluating a route to determine whether a dual facility will be good fit, the following items should be considered: • Merging zones • Exit and entrance ramps • Interchange ramps • Access to local interchanges • Results of heavy-truck flow survey • Results of toll analysis • Results of demand analysis • Overcoming problematic use of current ramps (may not be suitable for heavy trucks) Dual facilities offer a unique opportunity for handling nonrecurrent congestion.
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From page 104... ...
102 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Reduces Frequency of Incidents The safety benefits of separating auto and truck traffic may be one of the most important benefits of truck lanes (Fischer et al.
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From page 105... ...
103 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION The objective of reversible lanes is to address unbalanced flow, which typically occurs during the morning and evening peak travel times on routes heavily traveled by metropolitan commuters. The purpose is to match directional lane capacity to the proportion of directional traffic flow.
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From page 106... ...
104 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Design Criteria The AASHTO Green Book (2011) provides design guidance for HOV reversible configurations.
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From page 107... ...
105 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Cost Implementation of reversible lanes is widely considered one of the most cost-effective methods of increasing peak period capacity along existing streets. Several direct costs are associated with the maintenance and operations of reversible lanes: • Pavement construction (if applicable)
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From page 108... ...
106 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • Capacity decrease expected due to the work zone (e.g., one lane of a three-lane cross section is closed) • Capacity of the express lanes Cost The cost of installing a work-zone express lane will vary based on the length of roadway to be constructed, the availability of right-of-way, and the extent of traffic control needed.
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From page 109... ...
107 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION A recent FHWA report, Traffic Signal Preemption for Emergency Vehicles: A Cross-Cutting Study (2005) , identifies issues associated with emergency vehicle preemption.
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From page 110... ...
108 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Queue-Jump and Bypass Lanes Description and Objective Queue-jump lanes are built at congested intersections or ramps to allow transit vehicles, HOVs, or toll-paying vehicles to bypass the queue at the signal or ramp meter. One example of a queue-jump lane is a short lane provided at the signal approach and continued for a short distance beyond the signal.
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From page 111... ...
109 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Typical Applications Queue-jump lanes are installed at intersections. The queue-jump lane can be a rightturn-only lane that permits through movements for buses only.
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From page 112... ...
110 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • The intersection operates at Level of Service D or worse. • Lane acquisitions are feasible and costs are affordable.
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From page 113... ...
111 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • Length of queue-jump or bypass lane (longer lanes will be easier for emergency response personnel to access when queues exist) • Traffic demand levels • Incident frequency • Local policies encouraging or discouraging general traffic to bypass an incident by using the queue-jump lane Roadways with high frequencies of lane-blocking incidents, high-demand levels, and local policies encouraging general traffic to bypass an incident using the queuejump lane will be most positively affected by this treatment.
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From page 114... ...
112 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • Upgrading to signal controllers that can handle closed loop, responsive, or adaptive signal timing plans • Installing or upgrading vehicle detection at intersections (inductor loops or cameras) Treatments may also include improvements to the signal timing plan, such as the following: • Improving clearance intervals to maximize efficiency while taking safety concerns into consideration • Changing phasing to add or remove protected left turns • Implementing or improving coordination plans along a corridor • Implementing responsive or adaptive signal timing systems • Adjusting timing elements such as minimum green, maximum green, gap time, and overlaps • Providing pedestrian phases with pedestrian push buttons and signal heads In addition, automated enforcement for red light running or speed violations are signal-related improvements that may be implemented to reduce incidents caused or related to these violations.
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From page 115... ...
113 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Reduces Crash Frequency Improvements to traffic signals may lead to a reduction in total crashes. By eliminating crashes, this treatment eliminates the congestion associated with these crashes, thereby improving reliability.
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From page 116... ...
114 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Cost Signal timing improvements often have high benefit–cost ratios because the cost may be little more than a few hours of staff time to develop and implement an improved plan, although the benefit could be the reduction of several severe crashes. Improvements to vehicle detection (cameras or induction loops)
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From page 117... ...
115 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Adaptive systems do not necessarily have defined signal timing plans with a set cycle length or offsets. They do not have to move sequentially through a set of phases, because the controller can skip phases, or move back to a previous phase, to best minimize delay.
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From page 118... ...
116 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Cost The cost of implementing signal timing improvements varies considerably; it is most dependent on the type of controller and detection already present at the intersection. When these are already sufficient, closed loop responsive systems may be implemented for only the cost of the staff time required to develop timing plans and threshold criteria.
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From page 119... ...
117 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Reduces Frequency of Incidents Several sources indicate that ramp metering systems can reduce the number of crashes on a freeway segment (Minnesota Department of Transportation 2006)
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From page 120... ...
118 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION • Required improvements to facilitate communication between system parts • Construction costs such as the following o Controller o Signal heads o Detectors o Signing o Pavement markings o Communication infrastructure o Power source Temporary Traffic Signals Description and Objective Temporary traffic signals are provided at intersections for a limited period of time. Often, temporary span-wire signals are installed and used for the duration of a construction project.
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From page 121... ...
119 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Temporary signals for bridge construction are necessary for one-lane operations. The use of temporary signals on bridges allows road construction teams to remove flaggers from the field and dedicate synchronized signal timing between signal units.
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From page 122... ...
120 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION to be used to address weather issues, grade and roadway condition issues, or heavy traffic congestion (both recurrent and nonrecurrent)
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From page 123... ...
121 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Reduces Crash Frequency VSLs help smooth traffic speeds, decreasing the speed differential between fast-moving and slow-moving vehicles. This increase in speed uniformity may lead to a decrease in crash frequency.
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From page 124... ...
122 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Shifts Demand to Other Time Periods Electronic toll collection provides a means for counting the number of vehicles traveling along a given segment of roadway. This information can be used in conjunction with ITS to notify the traveling public of congested conditions.
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From page 125... ...
123 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Overheight Vehicle Detection and Warning Systems Description and Objective This treatment is designed to detect overheight vehicles and activate warning devices to alert those vehicles of oncoming overhead height restrictions. An overheight vehicle is any vehicle containing a load whose height (legal, permitted, or illegal)
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From page 126... ...
124 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Cost Cost estimates will vary depending on the type of system deployed. A simple, lowercost system could be an optical system, consisting of an activated flash beacon mounted above a static sign using solar power and wireless communication.
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From page 127... ...
125 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Reduces Incident Response Time Reference location signs allow people involved in or reporting an incident to provide detailed information about the exact location of the incident. This action results in faster response and clearance times, reducing congestion and improving reliability.
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From page 128... ...
126 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Reduces Mainline Demand During an Incident Reference location signs promote the communication of accurate incident location information that can be relayed to motorists through advanced traveler information systems such as dynamic message signs or local radio stations. When motorists are made aware of congested conditions along their route, they are able to divert to other routes, thereby reducing the mainline demand.
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From page 129... ...
127 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION The objective of roadside call boxes is to notify emergency personnel of an incident quickly, thus decreasing the response time of emergency personnel. The information relayed via a roadside call box may also be used by ITS to notify drivers of adverse conditions ahead (e.g., by using variable message boards or radio announcements)
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From page 130... ...
128 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Factors Influencing Treatment Effectiveness The following factors may influence the effectiveness of roadside call boxes at reducing nonrecurrent congestion: • Cell phone reception (the less reception available, the more useful this treatment will be) • Efficiency of notification system at relaying information to emergency responders • Traffic demand volumes • Presence of ITS • Capability of informing motorists of lane-blocking incidents through variable message signs or local radio • Frequency of call boxes and uniformity of identifying signs and locations Cost Cost estimates will vary depending on ownership (agency or private)
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From page 131... ...
129 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION In Best Practices for Road Weather Management, Goodwin (2003) describes how, from 1973 to 1994, there were 200 fog-related accidents with 130 injuries and 18 fatalities on I-75 in Tennessee.
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From page 132... ...
130 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Figure 4.19 presents a photo of a RWIS at Turner–Fairbank Highway Research Center. How Treatment Reduces Nonrecurrent Congestion Reduces Frequency of Incidents RWIS information can be used by maintenance crews to prepare for deicing, antiicing, and snow removal treatments in advance of a winter storm.
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From page 133... ...
131 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION Factors Influencing Treatment Effectiveness Factors that may influence the effectiveness of RWIS at reducing nonrecurrent congestion include the following: • Sophistication of system o Numbers and types of sensors o Accuracy of prediction models • Effectiveness of communication system between RWIS and maintenance personnel Cost The cost of an RWIS system varies depending on the size of the system, as well as weather-prediction model development and ongoing calibration. If certain infrastructure is already in place (e.g., ITS for managing freeway lanes and dispatching emergency personnel)
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From page 134... ...
132 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION How Treatment Reduces Nonrecurrent Congestion Reduces Number of Incidents Flood warning systems are designed to reduce the number of incidents related to flooded roadways and to prevent vehicles from driving into a situation in which they are "trapped" by a flooded roadway. Like other weather emergency treatments, such as gates that close freeway ramps during snowstorms and contraflow lanes during hurricane evacuations, this treatment is not designed to reduce trip delay or increase reliability, but rather to minimize incidents and improve safety.
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From page 135... ...
133 DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION discourage drivers from traveling during the windy conditions, or encourage them to find an alternative path or proceed with greater caution. How Treatment Reduces Nonrecurrent Congestion Reduces Number of Incidents Wind warning systems are designed to reduce the number of crashes and incidents caused by high winds.
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