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Benefit-Cost Analysis 61 Assessing what the minimum level of diversion would need to be in the case of LCV opera- tions to make truck-only lanes a viable investment option in comparison to additional mixed- flow lanes; Assessing optimal diversion rates for truck-only lanes that provide the highest levels of cost- effectiveness (for congested corridors with high truck volumes, very high diversion rates would not necessarily maximize cost-effectiveness since congestion reduction on the general purpose lanes due to truck diversion might be offset by high levels of congestion on the truck- only lanes--this would be particularly relevant in the case where use of the truck-only lanes is mandatory); and Assessing the differences in diversion rates required for truck lanes with and without LCV operations to achieve similar levels of cost-effectiveness in the case of long-haul corridors. 4.2 Performance Metrics Considered for Benefit-Cost Analysis The performance metrics discussed in the remainder of the following subsections were con- sidered for the B-C analysis of truck-only lanes. 4.2.1 Public Benefits Public benefits could include the following: Travel time savings that accrue to autos on general purpose lanes as trucks divert from general purpose lanes to truck-only lanes, thereby reducing congestion and improving travel speeds on the general purpose lanes. This metric is typically evaluated in terms of percent savings in travel times on the general purpose lanes due to the implementation of truck-only lanes. Reliability benefits that accrue to autos on general purpose lanes due to the implementation of truck-only lanes. The diversion of trucks to truck-only lanes reduces congestion and truck- auto interaction on the general purpose lanes, thereby improving safety and providing asso- ciated reliability benefits (in terms of reduction in incident-related nonrecurrent delay). This metric is typically evaluated in terms of percent savings in incident-related (nonrecurrent) delay on general purpose lanes due to the implementation of truck-only lanes. Safety benefits that accrue to all users. As discussed previously, the implementation of truck- only lanes can provide safety benefits on the general purpose lanes, since diversion of trucks to truck-only lanes would reduce congestion and truck-auto interaction on the general purpose lanes. This metric is typically evaluated in terms of percent reduction in total accidents (fatal acci- dents, if total accidents were not reported) on the general purpose lanes. Reduction in emissions due to improved travel speeds on the general purpose and truck-only lanes would be another important public benefit of implementing truck-only lanes. The capac- ity enhancement along a corridor due to the implementation of truck-only lanes would result in improved travel speeds for autos and trucks on the general purpose lanes, as well as for trucks using the truck-only lanes. This improvement in travel speeds is expected to directly contribute to a net reduction in emissions along the corridor. However, the B-C analysis conducted in this study did not include environmental benefits (reduced emissions) as a public benefit category, primarily because of the lack of data required to accurately estimate travel speeds on general pur- pose and truck-only lanes. Also, the capacity enhancement due to the implementation of truck- only lanes is expected to result in some induced traffic along the corridor, as well as the displacement of auto and truck traffic from other corridors. This resulting increase in total VMT along the corridor would offset some of the emissions reduction from improved travel speeds. However, without the availability of a travel demand model, the net impact of increased VMT and improved travel speeds on emissions could not be assessed as part of the current study. Also,