Identification and Evaluation of the Cost-Effectiveness of Highway Design Features to Reduce Nonrecurrent Congestion (2014) / Chapter Skim
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Pages 16-23
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16 The research team conducted a number of activities aimed at (1) gathering and synthesizing information on existing and promising design treatments and (2)
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17 The Project L03 relationships have the following general functional form, as shown in Equation 3.1: TTI 3.1% LHL+ dccrit 0.05en j k l Rn n n ( )
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18 data included all mainline freeway crashes that occurred within the limits of each roadway section of interest during the study period. Crash severity levels considered in the research were the following: • Total crashes (i.e., all crash severity levels combined)
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19 Each focus group meeting consisted of a 2-day visit. On the first day of the visit, the research team met with several highway agency staff experienced in geometric design, traffic operations, traffic management, or maintenance to review implemented or planned projects to reduce nonrecurrent congestion.
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20 knowledge in geometric design, traffic operations, and maintenance. Participants included Minnesota DOT staff from the Minneapolis–St.
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21 • Ramp closure • Ramp metering • Reversible lanes • Traffic signal improvements • Ramp metering • Variable speed limits List of Design treatments Using the results of the initial contacts and follow-up focus groups with highway agencies, the research team identified a list of design treatments to be further assessed in the research. The factors that were used as the basis for deciding which design treatments should be considered for assessment included the following: • Treatment is used (or can be used)
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22 Table 3.2. Candidate Design Treatments Considered in the Research Category Nonrecurrent Congestion Design Treatment Secondary Treatment Medians Median crossovers -- Movable traffic barriers Gated median barrier Extra-height median barriers Mountable or traversable medians Shoulders Accessible shoulder -- Drivable shoulder Alternating shoulder Portable incident screens Vehicle turnouts Bus turnouts Crash investigation sites Crash investigation sites -- Right-of-way edge Emergency access between interchanges -- Arterials and ramps Ramp widening -- Ramp closure Ramp terminal traffic control Ramp turn restrictions Detours Improvements to detour routes -- Truck incident design considerations Runaway truck ramp -- Construction Reduce construction duration Improved work site access and circulation Animal–vehicle collision design considerations Wildlife fencing, overpasses, and underpasses -- Weather Snow fences Fog detection Blowing sand treatment Roadway weather-information system Anti-icing systems Flood warning system Wind warning system Lane types and uses -- Contraflow lanes for emergency evacuation Contraflow lanes for work zones HOV lanes and HOT lanes Dual facilities Reversible lanes Work-zone express lanes (continued on next page)
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23 storage area for vehicle breakdowns, a safe stopping place for service assistance patrols, increased flexibility for work-zone operations, as well as the potential for use when needed as an additional through lane. Second, some design treatments provided primarily to reduce recurrent congestion have the potential for use to address nonrecurrent congestion, but require an explicit decision by the highway agency or traffic management center.
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