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112 The objectives of this study were to develop a range of plausible transportation energy scenarios for the 2050 time frame, examine potential challenges that different futures could pose for state departments of transportation, and iden- tify robust policy options to assist state DOTs in preparing for an uncertain energy future. To support this effort, the research team conducted extensive background research. This included a thorough review of recent progress and future prospects for conventional and alternative fuels and vehicle technolo- gies, an exploration of important socio-demographic fac- tors and ongoing policy debates likely to influence future energy and transportation outcomes, and an examination of ongoing trends in the evolution of state DOT activities and responsibilities. Though extensive, the research and analysis conducted for this study cannot be viewed as exhaustive. Transportation and energy systems intersect with each other and virtually all other aspects of our society, economy, and environment through a series of direct and indirect positive and negative feedback mechanisms that are not always well understood. The pace of technological innovation appears to be accelerating as well, increasing the likelihood of surprise developments leading to transformative shifts in transportation and energy use in future decades. Even with the research teamâs best efforts, it seems quite likely that this study will have omitted certain fac- tors and trends that in future decades will prove to be extremely influential for energy use in the transportation sector. In short, while the findings and results of this study should be very helpful in assisting state DOTs to develop more robust long-range plans, there are ample opportunities to extend and complement the results through additional research. Over the course of the study, members of the project panel and other experts and observers have suggested a series of specific issues that could benefit from further analysis. In this final chapter of the report, opportunities for follow-on research are briefly described that, from the perspective of the research team, appear most promising. Autonomous vehicles. Nascent autonomous- and connected-vehicle technology, if commercially successful, could transform passenger travel and goods movement in profound ways in the coming decades. The technology could affect, for example, the cost of driving, total travel, on-road fuel economy, traffic safety, effective throughput capacity on existing roadways, the cost and efficiency of moving goods by truck, travel options for those unable to drive on their own, available forms of transit service, models of shared auto ownership, requirements for parking capacity in dense urban areas, and patterns of low-density development in suburbs and exurbs. To date, however, there remains much uncer- tainty regarding the time frame over which autonomous- and connected-vehicle technologies might be deployed. Additionally, current thinking on the potential effects for many of the factors listed previously is largely speculative. To assist transportation agencies in better preparing for the potentially transformative effects of autonomous- and connected-vehicle technology, it could be helpful to con- duct additional research that could be structured similarly to this study. Specifically, the effort could include identify- ing a range of plausible futures for the development and adoption of autonomous- or connected-vehicle technology, examining the types of challenges or opportunities that the plausible futures could pose for transportation agencies, and examining appropriate policy responses. Future travel preferences. The future scenarios devel- oped in this study assume that past predictors of vehicle travel will generally hold in the coming yearsâfor example, that expected growth in population and the economy should lead to an increase in aggregate vehicle miles of travel. In the early 2000s, however, the rate of growth in vehicle travel slowed to some degree, and total vehicle travel actually declined in the latter part of the first decade of this century. While much of the decline can be attributed to spiking fuel prices followed by the most severe recession in a generation, some have suggested that shifting travel preferences among C H A P T E R 1 0 Promising Directions for Future Research
113 younger generationsâfor example, delays in applying for a driverâs license and greater reliance on social media as a pos- sible alternative to physical travelâmay also be playing a role. Additional research to better understand whether fun- damental shifts in travel preferences are occurring and, if so, what implications such shifts might have for transportation agencies, could be very helpful. Signposts to trigger deferred strategies for uncertain future impacts. In developing the framework to assist state DOTs in crafting robust long-term plans in the context of an uncertain energy future, the team outlined a number of possible signposts that DOTs might monitor to determine when it would be appropriate to pursue strategies aimed at uncertain future impacts. Assuming that many state DOTs would choose to develop their own signposts, the study did not craft a set of highly detailed signpost metrics, which could involve identifying required data and methods for computing metrics and specifying threshold values for triggering the implementation of strategies. Additional analysis to address such technical detailsâeither for spe- cific states or for the nation as a wholeâwould certainly be valuable. Evaluation of novel strategies. While many of the strate- gies discussed in this study, such as the use of fuel taxes to raise transportation revenue or the application of transportation demand management policies to provide alternative com- muting options, have been in use for many decades, others are relatively novel and in some cases have not yet been imple- mented anywhere in the United States. Examples in the lat- ter category include mileage-based user fees, vehicle feebates, and state production and distribution of alternative fuels. In reviewing an early version of this report, one of the project panel members suggested that it would be helpful to track and evaluate the early exploration of novel strategies by states to better understand their practical effects and to identify best practices as they emerge. The research team concurs that such evaluation and information sharing could serve as a helpful resource for state DOTs. General guide on long-range planning for an uncertain future. Several of the state DOT staff with whom the research team interacted over the course of the study suggested that the general approach to developing robust plans in prepara- tion for an uncertain energy future employed in the analysis would be broadly applicable for other DOT planning efforts as well. While it is possible to abstract the basic steps for such analysis through a careful review of this study, a shorter and more accessible document that outlines the methodology and considers how robust decision-making principles could be more broadly integrated in DOT planning processes would likely be a valuable contribution.