Guidelines for Quantifying Benefits of Traffic Incident Management Strategies (2022)

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54 Application and Assessment of FHWA TIM Benefit-Cost Tool The final publishing of the FHWA TIM Benefit-Cost Tool presented an opportunity for comparison with other TIM methods. This tool has six independent modules that allow users to prepare a BCA for eight TIM activities: 1. Safety Service Patrol (SSP) 2. Driver Removal Laws (DRL) 3. Authority Removal Laws (ARL) 4. Shared Quick Clearance Goals (SQCG) 5. Pre-established Towing Service Agreements (PTSA) 6. Dispatch Colocation (DC) 7. TIM Task Forces (TIM-TF) 8. Responder Training (TR) Part D.1 summarizes the project-level cost inputs across the eight TIM activities. Part D.2 summarizes segment-specific inputs, which drive project benefits. The example shared in the tool documentation only focuses on the SSP TIM activity (Figure D1). Part D.2 presents screen- shots and descriptions of the documentation related to the remaining seven TIM activities. Part D.3 outlines data input to the TIM SSP module based on the Maryland CHART I-495 data evaluated as a part of this study. Part D.4 summarizes the tool outcomes and places them in the context of results observed in this study using other methods. D.1 Cost Inputs For all TIM activities listed above, except SSP, a single cost input is available, the annual pro- gram cost. For SSP, users may input the annual program cost or provide more detailed inputs, including vehicle type, number of vehicles, and the following six cost types by patrol vehicle type (Figure D1): 1. Driver hourly rate 2. Working hours per day 3. Working days per month 4. Fuel use in gallons/month or cost in dollars/month 5. Maintenance cost per month 6. An “other cost” input D.2 Segment-Specific Inputs Data inputs for each roadway segment must parallel the project duration specified. The value of segmentation of a long stretch of road is to accurately reflect disparate lane counts, TIM effectiveness levels, or demand. Detailed segment-specific inputs center on roadway geometry, TIM program effectiveness, traffic information, and incident information. A P P E N D I X D

Application and Assessment of FHWA TIM Benet-Cost Tool 55   D.2.1 Roadway Geometry Inputs are the same across all eight TIM activities: roadway geometry, including the number of lanes, general terrain, horizontal curvature, and the number of ramps (Figure D2). e number of lanes input must be between two and six. Categories for terrain and horizontal curvature are listed below, respectively: • Flat, level, rolling hills, and mountainous. • Straight, mild curves, sharp curves. Tool documentation does not include information on how these data aect any specic TIM activity with regard to the realization of specic benets and quantication of benets. D.2.2 Trafc Information Inputs are also the same across all eight TIM activities (Figure D3). e rst input is the posted speed limit, which has no input range. Additionally, trac volume and truck percentage Figure D1. FHWA TIM-BC screenshot for SSP cost inputs. Figure D2. TIM-BC screenshot of roadway geometry inputs.

56 Guidelines for Quantifying Benets of Trafc Incident Management Strategies are requested for each operation time selected in the “Program Information” input, which is presented in Part D.2.4. Trac volume input ranges from 500 to 2,200 vehicles per hour per lane. Truck percentage input ranges from zero to 25%. e model also requests the user to identify the percentage of project duration that experi- ences nine dierent types of weather conditions: clear, light rain, heavy rain, light snow, heavy snow, fog, icy conditions, low visibility, and wind. e sum of these nine allocations should total 100%. As with roadway geometry, information is not available on how these data aect the benet of a specic TIM activity. D.2.3 Incident Information Inputs are the same across all eight TIM activities. The selection of the number of lanes in the roadway information tab determines the incident blockage severity input types. The number of lanes blocked will always be one less than the number of lanes specified in the roadway information, and never more than four lanes blocked. Consequently, no full Figure D3. TIM-BC screenshot of trafc information inputs.

Application and Assessment of FHWA TIM Benet-Cost Tool 57   facility closures are considered, nor when more than four lanes are blocked on a six-lane or greater facility. e specication of incident duration and the count is based on the presence of the TIM strategy to be assessed. e user must also input the percentage of all incidents categorized as secondary. Figure D4 shows the inputs for “AM Peak.” If TIM is active during other times, then inputs for each operation time are present in the tab. D.2.4 Program Information Inputs are identical for ve of the TIM activities but dier slightly for SSP, DRL, and ARL. All eight have an identical operational time input, which segments analyses to include any of the four options: AM peak, PM peak, weekday o-peak, and weekend. For SSP, the incident duration savings can be specied as a constant amount by type of lane blockage (in minutes) or as average minutes of reduction in the duration of incidents regardless of the number of lanes blockage. A screenshot is presented in Figure D5. For DRL, the project savings requires the following inputs: • e proportion of incidents that can be cleared by the driver (default 50%). e DRL does not benet the system when, for example, a tow truck is required. • e DRL compliance prior to (default 0%) and aer (default 50%) TIM activity in terms of percentage of vehicles. • e reduction in incident duration (default 5 minutes). For ARL, the project savings inputs are, in essence, the same. e only dierence is the before and aer “compliance rate” in DRL is called before and aer “implementation” in the ARL. is may be a developer error as the information buttons for both are identical (Figure D6). e remaining ve TIM activities have project savings inputs that are similar to ARL and DRL, without the before/aer inputs. Instead, they have a simple “Implementation” eld that has a default of 100% (Figure D7). is eld represents the proportion of cases in which clear- ance times are improved. e ve TIM activities are SQCG, PTSA, DC, TIM-TF, and TR. Figure D4. TIM-BC screenshot of incident information inputs.

58 Guidelines for Quantifying Benets of Trafc Incident Management Strategies Figure D5. TIM-BC SSP program information: two incident duration savings options. Figure D6. TIM-BC program savings inputs for driver and authority removal laws.

Application and Assessment of FHWA TIM Benet-Cost Tool 59   D.3 Applying FHWA TIM-BC Tool, SSP Module to Maryland Data As a part of the analyses of multiple methods in this research to estimate the delay, emissions, and secondary incident benets from TIM, data from Maryland, Seattle, and Texas were explored. e Maryland data, which included 1,130 incidents over 3 months, were processed and sub- sequently applied within the SSP module of the TIM-BC tool. For simplicity, the data are entered as a single segment for the length of the I-495 facility in Maryland. Figure D8 is the Figure D7. TIM-BC project savings input for ve TIM activities. Figure D8. SSP input MD CHART I-495 project data.

60 Guidelines for Quantifying Benets of Trafc Incident Management Strategies screenshot of the project details, including name, segment, study duration, and annual costs. An estimate of $12 million in annual operating cost is input as the total Maryland CHART’s TIM costs. Once project details are entered, segment-specic details are the second input. ese include roadway geometry, SSP information, trac information, weather information, and incident information. Each denition is presented below. D.3.1 Maryland I-495 Roadway Geometry TIM operations are present 24/7 in Maryland. Roadway geometry parameters are illustrated in the SSP roadway geometry screenshot (Figure D9). e information button species that the level terrain corresponds to a 2-mph reduction of free ow speed, and the mild horizontal curvature corresponds to a 5-mph reduction of free ow speed. e eect of ramp presence or segment length is not oered. D.3.2 Maryland I-495 SSP Program Information e granularity of data allows data entry across each category (AM peak, PM peak, weekday o-peak, and weekend), and consequently, all four operational times are selected. e tool requires input on the incident duration savings either by the duration of the incident or by lane closure. Within the research conducted for this study, three methods were specied for computing delay savings, and each used a dierent specication for incident duration savings: • e Khattak and Rouphail (2004) method assumed non-TIM incident duration is 25% greater than TIM incident duration. • e Sun et al. (2010) method assumed that TIM delay is double that of non-TIM but did not specify the incident duration savings based on an average 43% reduction in the average response time of 35 minutes and a 50% reduction in clearance time for an average 20-minute non-TIM clearance. is translates to an average reduction of 55% for incident response time. • e Chang and Raqib (2013) method also does not specify within computation an incident duration savings. A review of CHART reports suggests that the overall reduction in incident duration with CHART is 24.2% for the year 2012. Figure D9. SSP input MD CHART I-495 roadway geometry.

Application and Assessment of FHWA TIM Benet-Cost Tool 61   Based on the above three, a 25% incident duration savings is applied for all incidents. e data include incidents managed by CHART, including each incident duration. e following formula is applied to estimate the incident duration savings: Incident Duration without CHART = Average Incident Duration with CHART/0.75 Average Incident Duration Savings = 0.25 × Incident Duration without CHART Incident duration savings is computed by operational time (AM peak, PM peak, etc.), by incident type (shoulder, one lane blocked, two lanes blocked, etc.), and by incident duration. e TIM-BC tool requests the data by operational time, either by incident type or duration. Data specic to three or four lanes blocked are aggregated because the TIM-BC SSP tool does not allow for entry of full facility (four-lane) closures. e SSP program information entry screen- shot is presented in Figure D10. D.3.3 SSP Trafc Information Inputs in this section begin with the posted mainline speed limit. e speed limit on I-495 is 55 mph. e next sets of inputs are for trac volume and truck percentage by operation time. From the previous analysis, truck percentage and trac volume by incident were available by incident. e tool input is for the trac volume; however, the data available are for trac volume during incident. Input to the tool is 25% above the average trac volume for shoulder incidents. Using average plus standard deviation proved problematic because these data were not normally distributed for all operation times. e truck percentage is averaged across all incidents within each operation time. Weather information was not available; thus, “clear” was selected at 100% as a conservative estimate of SSP program benet. e data table for trac volume is in Figure D11, and the SSP trac information screenshot is presented in Figure D12. Figure D10. SSP input MD CHART I-495 program information.

62 Guidelines for Quantifying Benets of Trafc Incident Management Strategies Figure D11. MD CHART I-495 trafc volume and incident count by operation time. Figure D12. MD CHART I-495 SSP trafc information input.

Application and Assessment of FHWA TIM Benefit-Cost Tool 63   D.3.4 SSP Incident Information Incident count and duration by operational time and number of lanes blocked are the requisite inputs for this section. The final input is the percentage of estimated secondary incidents. Within the I-495 data, based on the CHART spatial and temporal identification of secondary incidents, 15% to 18% of the 1,130 incidents are secondary. The conservative 15% is applied within the TIM-BC SSP module. Figure D13 summarizes this data input. D.4 Results and Comparison The TIM-BC SSP tool presents online aggregate results, while the report download presented separate delay for passenger and truck vehicles. The screenshot in Figure D14 shows results within the online tool based on inputs specified for the Maryland CHART I-495 corridor. The BC ratio based on the inputs enumerated in Section D.3 is understated because the analysis herein did not have the cost of just SSP but rather an estimate of the complete program of ITS, including TIM, and the SSP coverage area that spans a freeway network well beyond the I-495 corridor. Without these corrections, the BC ratio is 2.84. Applying an estimate that the I-495 corridor is approximately 10% of the overall network for Maryland CHART SSP, the effective BC ratio is closer to 28.4. D.4.1 Comparison with Other Benefits Estimation Methods Estimates from the three delay methods applied in this study, along with the TIM-BC tool, are presented in Figure D15, adjusted to annualize results. Secondary accident reduction, emissions, and fuel consumption are also compared between the TIM-BC tool and the alter- nate methods evaluated in the conduct of this study. The TIM-BC tool estimate for passenger and truck delay reduction is within the previously identified range of benefit. The emissions and fuel savings outcomes are questionable. The negative values suggest an increase in fuel consumption and emissions from shortening inci- dent duration. The tool estimates of secondary incidents are far lower than that of all other methods assessed in the conduct of this study. Maryland Data (3 months) AM Peak Shoulder Number of Incidents 105 86 19 14 6 Average Duration (minutes) 7 25 32 81 67 PM Peak Number of Incidents 81 70 12 9 3 Average Duration (minutes) 9 17 32 65 52 Weekday Number of Incidents 310 218 59 63 25 Average Duration (minutes) 8 22 33 67 77 Weekend Number of Incidents 11 15 3 16 5 Average Duration (minutes) 8 32 47 71 257 Number of Lanes Blocked 1 Lane 2 Lane 3 Lane 4 Lane Figure D13. MD CHART I-495 incident data for SSP input.

64 Guidelines for Quantifying Benets of Trafc Incident Management Strategies Figure D14. SSP output from online interface. HC CO NO FHWA TIM-BC 1,126 FHWA TIM-BC 68 FHWA TIM-BC -0.76 -130.9 -0.4 FHWA TIM-BC -3.1 Chang 12,462 Mattingly 220 Chang 44.0 580.0 61.6 Chang 363.7 Sun 1,421 Sun 276 Morris 16.0 162.0 40.0 Khattak 14 Raub 216 Chou 164 Delay Reductions (Thousands of Vehicle Hours) Secondary Incident Reduction (count) Emissions Savings (Metric Ton) Fuel Savings (Thousands of Gallons) Comparison of Annualized Results from TIM-BC Tool with Various Methods Tested in Task 3 Figure D15. Comparison of annualized results from benets estimation methods.

Application and Assessment of FHWA TIM Benefit-Cost Tool 65   D.4.2 Use of Tool by Others The developers of the FHWA TIM-BC tool applied it to a 10-mile stretch of I-287 in New York and observed a SSP BC ratio of 18.4. The tool for this application advised adverse fuel consumption and emissions outcomes, but the developers explained that some incidents may have the effect of slowing down fast-moving traffic to more fuel-efficient speeds. Iowa DOT’s Office of Traffic Operations with the Center for Transportation Research and Education at Iowa State University applied the TIM-BC SSP module to evaluate Iowa DOT’s SSP program using 3 months of data (Khalilzadeh, 2020). The program provided SSP over a 49.4-mile bidirectional two- to three-lane freeway system equating to 98.9 directional miles with an annual cost of $3 million. While the analysis applied segment data for incident frequency, the average duration of incidents and the minutes saved from SSP were applied for all segments (Figure D16). The profile of reduction in incident duration is significantly different from that of the Maryland CHART I-495 data. Specific segment-level input data were not presented in the report. The overall BC ratio identified in the report is 76. A few factors may be driving this high ratio, most significantly that the incident duration savings are not input specific to peak and off-peak. Likely, the durations are far shorter in the peak periods prior to SSP with potentially lesser savings. Second, the duration of shoulder incidents prior to and after SSP is atypically high (4 hours versus 2 hours). The fuel consumption and emission benefits in this work are positive. D.5 Overall Findings The TIM-BC tool was completed in November 2015 and serves as the tool offered by the FHWA. The tool is based on over 160,000 simulation runs. Run outputs were used to develop the hybrid regression equations and look-up table processes. Application of data for one of the three regions assessed within this study, Maryland CHART I-495 corridor, suggests that the estimates of delay savings are conservative, and perhaps even more conservative for secondary incident reduction. The outcomes for fuel savings and environmental emissions are troubling, particularly given the speed limit of 55 mph in the region. Cost inputs for this tool are relatively clear and simple, requiring a singular input of cost for most TIM activities, with the exception of SSP. With SSP Without SSP With SSP Without SSP Shoulder 946 1056 118 230 One Lane Blocked 86 129 47 59 Two Lanes Blocked 10 40 61 70 All Incidents 1024 1225 112 207 112 12 9 95 *Without SSP data from Jan - Aug 2015 reported by agencies other than Highway Helper *With SSP data from Aug to November 2015 where Highway Helper responded Incident Count Incident Duration Incident Duration Savings (minutes) Incident Data for Iowa DOT SSP Figure D16. Incident data from Iowa DOT SSP evaluation.