Decarbonizing the grid. Although electrification of LDVs could achieve deep cuts in CO 2 emissions 10-12 , BEV diffusion will be ineffective if it occurs in regions with high-carbon electricity. Optimistic scenarios 1,9 show global BEV shares reaching 90% by 2050, abating 4 Gt of CO 2 . These scenarios assume that global average electricity CO 2 intensity must drop below 100 g CO 2 kWh -1 by 2050 from a current average of ~500 g CO 2 kWh -1 . That is a fivefold decrease within 40 years. Most industrialized countries are now entering a new power-generation investment cycle that represents an opportunity to deploy clean and efficient power-generation technologies. This is important, because power-generation investment decisions taken over the next 10 years will lock-in CO 2 emissions for the next 40-50 years 15 . The planning horizon for the vehicle-fleet cycle is 12-15 years. Electricity generation decisions must therefore be made within the next 10 years if it is to be aligned with the next two to three vehicle-fleet cycles where large-scale commercialization of BEVs is expected.

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The transition to a low carbon transport world requires a host of demand and supply policies to be developed and deployed. Pricing and taxation of vehicle ownership plays a major role, as it affects purchasing behavior, overall ownership and use of vehicles. There is a lack in robust assessments of the life cycle energy and environmental effects of a number of key car pricing and taxation instruments, including graded purchase taxes, vehicle excise duties and vehicle scrappage incentives. This paper aims to fill this gap by exploring which type of vehicle taxation accelerates fuel, technology and purchasing behavioral transitions the fastest with (i) most tailpipe and life cycle greenhouse gas emissions savings, (ii) potential revenue neutrality for the Treasury and (iii) no adverse effects on car use.The UK Transport Carbon Model was developed further and used to assess long term scenarios of low carbon fiscal policies and their effects on transport demand, vehicle stock evolution, life cycle greenhouse gas emissions in the UK. The modeling results suggest that policy choice, design and timing can play crucial roles in meeting multiple policy goals. Both CO2 grading and tightening of CO2 limits over time are crucial in achieving the transition to low carbon mobility. Of the policy scenarios investigated here the more ambitious and complex car purchase tax and feebate policies are most effective in accelerating low carbon technology uptake, reducing life cycle greenhouse gas emissions and, if designed carefully, can avoid overburdening consumers with ever more taxation whilst ensuring revenue neutrality. Highly graduated road taxes (or VED) can also be successful in reducing emissions; but while they can provide handy revenue streams to governments that could be recycled in accompanying low carbon measures they are 2 of 32 likely to face opposition by the driving population and car lobby groups. Scrappage schemes are found to save little carbon and may even increase emissions on a life cycle basis.The main policy implication of this work is that in order to reduce both direct and indirect greenhouse gas emissions from transport governments should focus on designing incentive schemes with strong up-front price signals that reward 'low carbon' and penalize 'high carbon'. Policy instruments should also be subject to early scrutiny of the longer term impacts on government revenue and pay attention to the need for flanking policies to boost these revenues and maintain the marginal cost of driving.

Current debate focuses on the need for the transport sector to contribute to more ambitious carbon emission reduction targets. In the UK, various macro-economic and energy system wide, top-down models are used to explore the potential for energy demand and carbon emissions reduction in the transport sector. These models can lack the bottom-up, sectoral detail needed to simulate the effects of integrated demand and supply-side policy strategies to reduce emissions. Bridging the gap between short-term forecasting and long-term scenario "models", this paper introduces a newly developed strategic transport, energy, emissions and environmental impacts model, the UK Transport Carbon Model (UKTCM). The UKTCM covers the range of transportenergy-environment issues from socio-economic and policy influences on energy demand reduction through to lifecycle carbon emissions and external costs. The model is demonstrated in this paper by presenting the results of three single policies and one policy package scenario. Limitations of the model are also discussed. Developed under the auspices of the UK Energy Research Centre (UKERC) the UKTCM can be used to develop transport policy scenarios that explore the full range of technological, fiscal, regulatory and behavioural change policy interventions to meet UK climate change and energy security goals.

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