User-Friendly Traffic Incident Management (TIM) Program Benefit-Cost Estimation Tool

APPENDIX B: INCIDENT DURATION ESTIMATION FOR IMPLEMENTING DIFFERENT TIM STRTEGIES

General Methodology for Quick-Clearance Traffic Incident Management Strategies

A given incident scenario, supplied among the currently required user inputs of the TIM-BC tool, represents the status quo of the highway segments before one of the considered TIM strategies is implemented. Given a set of assumptions and estimates for the mechanisms and effectiveness of a particular TIM strategy, the proportion of incidents in the incident scenario is modified to reflect the state of affairs after the implementation of that strategy. That is, each new TIM strategy will reduce the duration of some portion of incidents in the sample commensurate with the assumptions made about that strategy’s effectiveness. This adjusted incident duration is then used to estimate the total travel delay and fuel consumption after implementation and BC calculations in the methodology section.

It is the task for the TIM-BC tool developers to supply or request of the user the appropriate assumptions and estimates for each considered quick clearance TIM strategy. These assumptions and user inputs shall address the following issues for each proposed TIM strategy:

• The criteria for selecting the incidents susceptible to change by the strategy (applicable cases).
• The success rate of the strategy among applicable cases.
• The magnitude of improvement for incidents that successfully implemented a TIM strategy.

It should be noted that the results for different TIM strategies are not additive. This is because the benefits of different TIM strategies may not be independent of each other. As such, BC ratios calculated with the sum of benefits from various strategies represent a best case scenario where the benefits are assumed to be independent. While such a result may be useful, the actual combined benefit of those strategies is likely less than the total sum benefits of each applied strategy.

Driver Removal Laws

Driver removal laws require or encourage drivers whose vehicles are involved in a traffic incident to move their vehicles from the mainline of a highway to the shoulder when they are able to do so. The TIM-BC tool developer supplied assumptions and user inputs address the general TIM strategy issues as follows:

• The proportion and severity of incidents that could be cleared by the relevant driver(s).
  • Supplied by user.
  • Assumes (based on the panel interviews) that incidents in which there were no injuries and claims less than $500 could be cleared by drivers.
• The driver compliance rate among applicable cases before and after the proposed DRL program.
  • Supplied by user.
  • Before rate equals zero if no DRL exists.
• The average time for drivers to move a vehicle from the mainline to the shoulder:
  • Supplied by default.
  • Assumes incidents are cleared by drivers in five minutes, after which incidents are considered shoulder incidents.

A Calculation Example

Assume, for example, that the local effectiveness of DRLs is as follows:

• The user estimates that one-half of all one-lane incidents are made shorter by driver removal.
• There is currently no existing DRL and the proposed program has a compliance rate of 30 percent.

It is assumed that, during the AM peak time period, there are 20 one-lane incidents with an average duration of 35 minutes; and there are 25 shoulder incidents with an average duration of 30 minutes for the study period. The duration of half (10) of the one-lane incidents could be reduced (i.e., driver removal is possible) to 5 minutes as a result of applying driver removal laws. Of these incidents, 30 percent are cleared by compliant drivers; i.e., three incidents. Travel delays for the improved case are calculated with the following adjusted values. After implementation of DRLs, there are:

• Seventeen (20 – 3 = 17) one-lane incidents with a duration of 35 minutes.
• Three (0 + 3 = 3) one-lane incidents with a duration of 5 minutes that are then moved to the shoulder.
• Twenty-five shoulder incidents with a duration of 30 minutes (unchanged).
• Three hypothetical shoulder incidents with a duration of 30 minutes.

The benefit from the DRL is limited to the three one-lane incidents that were moved. As such, the 17 unchanged incidents are not part of the benefit calculation for travel delay and fuel consumption. So, the total benefits of applying the driver removal law is the difference between benefits from reduced duration of the mainline incident and the cost (lost benefits) from an extra shoulder incident due to driver removal laws.

In the example above, the benefit of moving three one-lane incidents to the shoulder is calculated as the number of incidents successfully implementing the DRL (3 = 20 * 0.5 * 0.3) and the calculated average incident duration savings (30 = 35 – 5). The costs or lost benefits due to moving those incidents to the shoulder are calculated as the cost of three hypothetical shoulder incidents of 30-minute duration. This represents the remaining time to clear the incident from the shoulder. For the example above, if the travel delay savings for the one-lane reductions were 4,000 vehicle hours and the increased travel delay for the hypothetical shoulder incidents were 2,200, the actual benefit in travel delay of the driver removal program would be 1,800 vehicle hours (4,000 – 2,200). The calculated travel delay savings are used to directly compute corresponding fuel savings.

The calculation of secondary incident savings proceeds as with the TIM-BC tool, with the exception that the lost benefits due to moving to the shoulder must be deducted from the total travel delay and fuel consumption values. Put another way, there is no calculation of secondary savings from the hypothetical shoulder incidents. Rather, the impact of the driver removal strategy on secondary incidents is that of the one-lane savings alone, after accounting for benefits lost.

Authority Removal Laws

Authority removal laws give TIM responders some measure of authority to have vehicles, debris, and/or spilled cargo removed from the road when the owners are unwilling or unable to do so in a timely fashion. The TIM-BC tool’s developer-supplied assumptions and user inputs address the authority removal laws as follows:

• The proportion and severity of incidents that could be reduced by exercising removal authority.
  • Supplied by user.
  • Supplied by default to be 30 percent of all incidents.
• The proportion of applicable cases for which ARL could be exercised.
  • Supplied by user.
  • Supplied by default to be 100 percent of incidents.
• The average time for vehicles to be moved to shoulder.
  • Supplied by user.
  • Supplied by default to be 10 minutes.
  • For the default value, incidents are cleared in 10 minutes. After 10 minutes, these incidents are considered shoulder incidents.

A Calculation Example

Assume, for example, that the local effectiveness of ARLs is as follows:

• The user accepts the default value that 30 percent of incidents in all severity classes are mitigated by authority removal.
• There is currently no existing law and the proposed program is effective in 100 percent of the applicable cases.

It is assumed that, during the AM peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes for the study period. The duration of 30 percent of the one-lane incidents (six) and two-lane incidents (three) could be reduced to 10 minutes as a result of authority removal. All of these incidents are moved to the shoulder via authority remova laws. Travel delays for the improved case are calculated with the following adjusted values:

• Fourteen (20 – 6 = 14) one-lane incidents with a duration of 35 minutes.
• Seven (10 – 3 = 7) two-lane incidents with a duration of 45 minutes.
• Six one-lane incidents with a duration of 10 minutes.
• Three two-lane incidents with a duration of 10 minutes.
• Twenty-five shoulder incidents with a duration of 30 minutes (unchanged).
• Six shoulder incidents with a duration of 25 minutes.
• Three shoulder incidents with a duration of 35 minutes.

The benefits from the ARL strategy are from the six one-lane and three two-lane incidents that were the implemented strategy. As such, the other unchanged incidents are not part of the benefit calculation for travel delay and fuel consumption. In general, the total travel delay and fuel savings are calculated as the total benefit of shortening the one- and two-lane incidents minus the benefits loss of extra shoulder incidents due to moving those mainline incidents to the shoulder. The benefits loss due to moving a mainline incident to the shoulder are calculated as the negative of the hypothetical benefits of completely reducing the duration of the same number of shoulder incidents to zero for one- and two-lane incidents, respectively.

In the example above, the benefit of moving the one-lane and two-lane incidents to the shoulder is calculated as number of incidents implemented ARL (20 * 0.3 * 1.0 = 6; 10 * 0.3 * 1.0 = 3) for one- and two-lanes, respectively, and the calculated average incident duration savings, (35 – 10 = 25 (one lane); 45 – 10 = 35 (two lanes)). The lost benefits due to moving those incidents to the shoulder is calculated as the extra travel delays due to six (from one-lane incident) hypothetical shoulder incidents with a duration of 25 minutes and three (from two-lanes incident) shoulder incidents with a 35-minute duration. The total savings in travel delay and fuel consumption of applying the authority removal law are the difference between travel delays and fuel consumption that resulted in mainline and shoulder incidents. For the example above, if the total travel delay savings for the one- and two-lane reductions were 4,000 vehicle hours and the extra delays of hypothetical amount of shoulder incidents were 800 (from one lane incidents) and 600 (from two lane incidents), the actual benefit in travel delay of the authority removal program would be 2,600 vehicle hours (4,000 – 800 – 600 = 2,600).

The calculation of secondary incident savings proceeds as with the TIM-BC tool, with the exception that the lost benefits due to moving to the shoulder must be deducted from the total travel delay and fuel consumption values. Put another way, there is no calculation of secondary savings from the hypothetical shoulder incidents. Rather, the impact of the authority removal strategy on secondary incidents is that of the one-lane and two-lane savings alone, after accounting for benefits lost.

Shared Quick-Clearance Goals

Some TIM management areas with coordinated, interdisciplinary TIM response structures adopt shared quick-clearance goals to improve clearance time across all incident types. The TIM-BC tool developer-supplied assumptions and user inputs shall address the following issues for this TIM strategy:

• The proportion and severity of incidents that could be improved by adopting shared quick-clearance goals.
  • Supplied by user.
  • Supplied by default as all incidents.
• The proportion of applicable cases in which clearance times are improved.
  • Supplied by user.
  • Supplied by default as all incidents.
• The average improvement in clearance times.
  • Supplied by user.
• Supplied by default to be 10 minutes.

A Calculation Example

Assume, for example, that the local effectiveness of shared quick-clearance goals is as follows:

• The user accepts the default value that all incidents can be reduced by adopting quick- clearance goals.
• The user accepts the default value that clearance times are improved in all applicable cases.
• The user accepts the default value that incidents are improved, on average, by 10 minutes.

It is assumed that, during the morning peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes. Travel delays for the applicable case are calculated as follow:

• Twenty-five shoulder incidents with a duration of 20 (30 – 10 = 20) minutes.
• Twenty one-lane incidents with a duration of 25 (35 – 10 = 25) minutes.
• Ten two-lane incidents with a duration of 35 (45 – 10 = 35) minutes.

These adjusted values are used in the calculations of total savings for travel delay, fuel consumption, emissions, and secondary incidents.

Preestablished Towing Service Agreements

Preestablished towing service agreements between TIM management agencies and local towing services promote, via contractual obligation, the level of service that those companies must provide. These obligations are usually set in terms of tow vehicle availability and response times. The TIM-BC tool developer-supplied assumptions and user inputs should address the following issues for this TIM strategy:

• The proportion and severity of incidents that require towing services.
  • Supplied by user.
  • Supplied by default as all incidents of one-lane severity or greater.
• The proportion of applicable cases in which clearance times are improved.
  • Supplied by user.
  • Supplied by default as all incidents.
• The average improvement in clearance times.
  • Supplied by user.
  • Supplied by default as 10 minutes.

A Calculation Example

Assume, for example, that the local effectiveness of towing agreements is as follows:

• The user accepts the default value that all incidents of one-lane severity or greater are improved by preestablished towing agreements.
• The user accepts the default value that incident durations are reduced, on average, by 10 minutes.

It is assumed that, during the morning peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes. Travel delays for the implemented towing service cases are calculated as follow:

• Twenty-five shoulder incidents with a duration of 30 minutes (no change).
• Twenty one-lane incidents with a duration of 25 (35 – 10 = 25) minutes.
• Ten two-lane incidents with a duration of 35 (45 – 10 = 35) minutes.

These adjusted values are used in the calculations of total savings for travel delay, fuel consumption, emissions, and secondary incidents.

Dispatch Colocation

Colocation of dispatch personnel and equipment can improve communication between responders, thus decreasing dispatch and initial response times. The following are TIM-BC tool developer-supplied assumptions and user inputs address this TIM strategy issues:

• The proportion and severity of incidents that are potentially improved by colocation.
  • Supplied by user.
  • Supplied by default as all incidents of two-lane severity or greater.
• The proportion of applicable cases that are actually improved by colocation.
  • Supplied by user.
  • Supplied by default as all incidents.
• The average improvement in clearance time for applicable cases.
  • Supplied by user.
  • Supplied by default to be 10 minutes.

A Calculation Example

Assume, for example, that the local effectiveness of dispatch colocation is as follows:

• The user accepts the default value that durations of all incidents of two-lane severity or greater are reduced by dispatch colocation.
• The user accepts the default value that incident durations are reduced, on average, by 10 minutes.

It is assumed that, during the morning peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes. Travel delays for the improved case are calculated as follows:

• Twenty-five shoulder incidents with a duration of 30 minutes (no change).
• Twenty one-lane incidents with a duration of 35 minutes (no change).
• Ten two-lane incidents with a duration of 35 (45 – 10 = 35) minutes.

These adjusted values are used in the calculations of total savings for travel delay, fuel consumption, emissions, and secondary incidents.

TIM Task Forces

TIM task forces are groups of TIM-related planners, managers, and other personnel that meet periodically to coordinate activities and policies. The TIM-BC tool developer-supplied assumptions and user inputs address the general TIM strategy issues as follows:

• The proportion and severity of incidents that are potentially improved by the activities of task forces.
  • Supplied by default (by user or tool) as all incidents.
• The proportion of applicable cases that are actually improved by task forces.
  • Supplied by default (by user or tool) as all incidents.
• The average improvement in clearance time for applicable cases.
  • Supplied by default (by user or tool) to be 10 minutes.

A Calculation Example

Assume, for example, that the local effectiveness of TIM task forces is as follows:

• The user accepts the default value that all incidents are improved by TIM task force activities.
• The user accepts the default value that incident durations are reduced, on average, by 10 minutes.

It is assumed that, during the AM peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes. Travel delays for the TIM task forces case are calculated as follows:

• Twenty-five shoulder incidents with a duration of 20 (30 – 10 = 20) minutes.
• Twenty one-lane incidents with a duration of 25 (35 – 10 = 25) minutes.
• Ten two-lane incidents with a duration of 35 (45 – 10 = 35) minutes.

These adjusted values are used in the calculations of total savings for travel delay, fuel consumption, emissions, and secondary incidents.

SHRP2 Training

The second Strategic Highway Research Program (SHRP2) National Traffic Incident Management Responder Training focuses on motorist and responder safety while minimizing an incident’s impact on traffic flows. The TIM-BC tool developer-supplied assumptions and user inputs address the following issues for this TIM strategy:

• The proportion and severity of incidents that are potentially improved by training.
  • Supplied by default (user or tool) as all incidents.
• The proportion of applicable cases that are actually improved by training.
  • Supplied by default (user or tool) as all incidents.
• The average improvement in clearance time for applicable cases.
  • Supplied by default (user or tool) to be 10 minutes.

A Calculation Example

Assume, for example, that the local effectiveness of SHRP2 training is as follows:

• The user accepts the default value that all incidents are improved by SHRP2 training.
• The user accepts the default value that incident durations are reduced, on average, by 10 minutes.

It is assumed that, during the AM peak time period, there are 20 one-lane incidents with an average duration of 35 minutes, 10 two-lane incidents with an average duration of 45 minutes, and 25 shoulder incidents with an average duration of 30 minutes. Travel delays and fuel consumption for the cases applied to SHRP2 training are calculated as follows:

• Twenty-five shoulder incidents with a duration of 20 (30 – 10 = 20) minutes.
• Twenty one-lane incidents with a duration of 25 (35 – 10 = 25) minutes.
• Ten two-lane incidents with a duration of 35 (45 – 10 = 35) minutes.

These adjusted values are used in the calculations of total savings for travel delay, fuel consumption, emissions, and secondary incidents.