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50 Quick-Sketch Method to Estimate TIM Program Benefits The Quick Benefits Analysis Method (QBAM) takes the overall delay estimate from a metro- politan area or corridor and applies several âfactorsâ to the delay to determine what percentage of that delay that TIM activities being evaluated might reasonably be expected to reduce, or alternatively, how much more delay would be present without the TIM activities being evaluated. The factors are based on the rules of thumb that have been established in the TIM industry. The result is a delay savings estimate that can be subsequently used to estimate emissions and fuel savings and even be monetized using spreadsheet-based techniques. The basic steps of QBAM are shown in Figure B1. The process starts with a total annual traffic congestion delay for the region, and then derives the amount of that delay that can be saved by the TIM activities being considered. This is done through simple multiplication of the rules of thumb factors and an approximation of the coverage area and temporal scope of the evaluated TIM activities. Two common rules of thumb can be applied or adjusted as needed: 1. Highway incidents cause about 25% of the total congestion (delay). Apply to step 2. 2. Implementation of TIM tactical activities can reduce incident-related delays by 15%. Apply to step 3. The second rule of thumb may be considered the TIM effectiveness factor. Note that more than one factor may be applied in step 3: a geographic scope factor, temporal coverage factor, and an effectiveness factor. Note that the 15% factor can be raised or lowered based on the strategies being proposed and evaluated. If the change in TIM service being proposed is relatively minor, then the evaluator should reduce the effectiveness factor accordingly. On the other hand, if the proposed change involves more aggressive service patrolling in combination with other activities, then one might consider raising the effectiveness factor. Again, the idea with this method is to come up with a quick estimate; it should be understood that the estimate is appropriate for strategic planning and not operations or investment analysis. Some things to keep in mind when considering the use of this method: ⢠The method can be applied very quickly but only provides a rough ballpark estimate. ⢠Robust incident or demand data are not needed to use this method; however, if available, such data can be used for reasonableness checks on the results. ⢠If possible, compare this result with the results of other methods. ⢠Approximations and assumptions will need to be used to fine-tune the factors based on the TIM activities being evaluated, the time periods for which the strategies are being consid- ered, and the local traffic demand, network, and incident characteristics. To demonstrate the QBAM, the research team used the data collected in Dallas and Seattle. The source used for the overall delay was taken from the most recently updated Texas A&M A P P E N D I X B
Quick-Sketch Method to Estimate TIM Program Benets 51Â Â Transportation Institute (TTI) Urban Mobility Report (2014). e factors used and the results are shown in Table B1. Note that the result in both cases was within the range of the results from the more data- intensive methods that were tested. us, with a small amount of eort, the research team was able to produce a result that seems reasonable in comparison to the results from the more complex, analytical methods that in their development applied simulation and mathematical models. Depending on the level of rigor needed in an analysis, the QBAM may be good enough. Find total annual traffic delay in urban area or corridor Figure B1. Quick-sketch method procedure. Region TTI Annual Vehicle-Hours of Delay (2014) % Delay Caused by Incidents Rule of Thumb % Incident Delay within Subnetwork Estimate % Delay Savings Due to TIM Estimate Annual Delay Reduction with TIM (vehicle- hours/year) Seattle, WA 139,842,136 Ã 25% Ã 10% Ã 15% = 529,400 Dallas, TX 186,535,000 Ã 25% Ã 15% Ã 15% = 1,049,300 Table B1. Factors selected in application of TIM QBAM.