Guidelines for Quantifying Benefits of Traffic Incident Management Strategies (2022) / Chapter Skim
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Pages 29-37
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From page 29... ...
29 TIM Analysis Step 2 -- Planning the TIM Analysis Planning the analysis enables the TIM analysts and program managers to develop meaningful results from the analysis within the scope of available data, expertise, funding, and time. At this point, the TIM program manager and/or analyst should have a strong understanding of the problem to be addressed, the goals of the analysis, the desired products from the analysis, and potential resources available for the analysis.
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From page 30... ...
30 Guidelines for Quantifying Benefits of Traffic Incident Management Strategies based on previous empirical and simulation activities or mathematical modeling were com pared using common data sets with the goal of understanding the strengths and limitations of these methods, and documenting the level of effort, complexity, and data needs to support the use of these methods. Four methods for estimating secondary incidents, three methods for estimating delay, and two methods for estimating emissions were applied to three corridors: one from Maryland, Washington State, and Texas.
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From page 31... ...
TIM Analysis Step 2 -- Planning the TIM Analysis 31 Safety: Identifying Secondary Crashes When possible, rely on direct reporting or logging of secondary crashes from law enforcement, TMC operator, and service patrol before and after TIM implementation. After-the-fact methods to identify which incidents are secondary are provided below.
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From page 32... ...
32 Guidelines for Quantifying Benefits of Traffic Incident Management Strategies Method Strengths Limitations Data Needs Sun et al., 2010 "Equation based on change in incident duration and excess demand" Simple to apply Does not require incident duration data Considers events up to three lanes blocked Assumes no delay if demand is less than the reduced capacity from the incident • Incident duration with TIM • Incident duration without TIM • Traffic demand • Reduced capacity Khattak and Rouphail, 2004 "Delay a function of volume capacity ratio" Different equation parameters based on urban/rural, incident duration, and lane blockage Assumes non-TIM is 1.25 times TIM incident duration Covers incidents blocking up to two lanes Computes delay for incidents up to 60 minutes in duration • Area type -- urban or rural • Number of lanes • Incident duration rounded to 15 minutes • Number of lanes and lanes blocked • Traffic volume and capacity Environment: Quantifying Reduction in Emissions and Fuel Use A secondary but important benefit from TIM. Consider use of rules of thumb for this estimation based on delay.
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From page 33... ...
TIM Analysis Step 2 -- Planning the TIM Analysis 33 ICT may have increased during the first winter with TIM, when compared to the previous winter without TIM, because of multiple major snowstorms, resulting in more complex incidents than the previous winter. Define Homogeneous Road Segments Typically, data available for analysis will not have full incidentspecific information such as demand and speed prior to and after each incident.
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From page 34... ...
34 Guidelines for Quantifying Benefits of Traffic Incident Management Strategies In summary, data sets central to TIM analysis are those with variables pertinent to the outcomes of interest. The basic data sets and data fields needed include: • Incident data -- start time, stop time, location, lanes blocked, primary or secondary classification, type (crash, injury, fatality, etc.)
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From page 35... ...
TIM Analysis Step 2 -- Planning the TIM Analysis 35 In Table 7 are strategies to overcome the absence of specific data, and strategies to fill gaps from missing data. Note, without incident duration data, the estimate of benefits is closer to a sketchlevel analysis as compared to an operations assessment.
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From page 36... ...
36 Guidelines for Quantifying Benefits of Traffic Incident Management Strategies Data Type What If Data Are Not Available? How To Overcome Incomplete or Missing Data Incident Duration Consider using state or regional incident duration estimates based on incident severity and lane closure types.
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From page 37... ...
TIM Analysis Step 2 -- Planning the TIM Analysis 37 Data Required To Estimate Traveler Satisfaction Outcomes Typically, traveler satisfaction is measured through surveys. In addition, agencies that allow travelers to post feedback using social media or websites can use that information as part of the assessment of traveler satisfaction.
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