# The effect of complex models of externalities on estimated optimal tolls

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## Abstract

Transport externalities such as costs of emissions and accidents are increasingly being used within appraisal and optimisation frameworks alongside the more traditional congestion analysis to set optimal transport policies. Models of externalities and costs of externalities may be implemented by a simple constant cost per vehicle-km approach or by more complex flow and speed dependent approaches. This paper investigates the impact of using both simple and more complex models of CO_{2} emissions and cost of accidents on the optimal toll for car use and upon resulting welfare levels. The approach adopted is to use a single link model with a technical approach to the representation of the speed-flow relationship as this reflects common modelling practice. It is shown that using a more complex model of CO_{2} emitted increases the optimal toll significantly compared to using a fixed cost approach while reducing CO_{2} emitted only marginally. A number of accident models are used and the impact on tolls is shown to depend upon the assumptions made. Where speed effects are included in the accident model, accident costs can increase compared to the no toll equilibrium and so tolls should in this case be reduced compared to the congestion optimal toll. Finally it is shown that the effect of adding variable CO_{2} emission models along with a fixed cost per vehicle-km for accidents can increase the optimal toll by 44% while increasing the true welfare gained by only 8%. The results clearly demonstrate that model assumptions for externalities can have a significant impact on the resulting policies and in the case of accidents the policies can be reversed.

## Keywords

Congestion Externalities Optimal tolls Accidents Emissions## Notes

### Acknowledgements

The author thanks The Institute for Transport Studies for funding this research under its departmental fellowship. He would also like to thank colleagues Tony May, Chris Nash, Dave Watling and Agachai Sumalee and Erik Verhoef of FUA for useful comments on an early version of this paper. The author is also grateful to Guenter Emberger and Pauli Pfeffenbichler of TUW for their help and contribution to the MARS modelling of Edinburgh. The author also acknowledges the useful comments received from the referees that helped improve the paper. Any errors or shortcomings are, of course, the sole responsibility of the author.

## References

- Arnott, R.J., de Palma, A., Lindsey, R.: Departure time and route choice for the morning commuter. Transp. Res. B
**24**(3), 209–228 (1990)CrossRefGoogle Scholar - Bates, J., Brewer, M., Hanson, P., McDonald, D., Simmonds, D.C.: Building a strategic model for Edinburgh. In: Proceedings of Seminar D, PTRC Summer Annual Meeting. PTRC, London (1991)Google Scholar
- Beser, M., Algers, S.: SAMPERS, the new Swedish national travel demand forecasting tool. In: Lundkvist, L., Mattsson, L.-G. (eds.) National Transport Models: Recent Developments and Prospects. Springer Verlag (2001)Google Scholar
- Bickel, P., Schmid, S., Krewitt,W., Friedrich, R. (eds.): External costs of transport in externE. Final Report. IER, Stuttgart (1997)Google Scholar
- Chen, M., Bernstein, D.H., Chien, S.I.J., Mouskos, K.C.: Simplified formulation of the toll design problem. Transp. Res. Rec.
**1667**, 88–95 (1999)CrossRefGoogle Scholar - De Borger, B., Proost, S.: Reforming Transport Pricing in the European Union. Edward Elgar Publishing Limited, Cheltenham (2001). ISBN 1840641290Google Scholar
- Department for Environment, Transport and the Regions: Understanding the new approach to appraisal. London, DETR (1998)Google Scholar
- Department for Transport: Transport user benefit calculation: tag unit 3.5.3. Department for Transport, Transport Analysis Guidance TAG. http://www.webtag.org.uk (2004)
- Elvik, R.: Which are the relevant costs and benefits of road safety measures designed for pedestrians and cyclists? Accid. Anal. Prev.
**32**, 37–45 (2000)CrossRefGoogle Scholar - Emberger, G., Shepherd, S.P., Zhang, X.: Method to identify optimal land use and transport policy packages. Introduction of an indicator/target based appraisal approach. In: Proceedings 8th International conference on Computers in Urban Planning and Urban Management, CUPUM’03 SENDAI, Japan, 27–29 May 2003Google Scholar
- European Conference of Ministers of Transport: Efficient transport for Europe. Policies for internalisation of external costs. Paris (1998)Google Scholar
- Eyre, N.J., Ozdemiroglu, E., Pearce, D.W., Steele, P.: Fuel and location effects on the damage costs of transport emissions. J. Transp. Econ. Policy
**31**, 5–24 (1997)Google Scholar - Government Economic Service.: Estimating the social cost of carbon emissions (2002). GES Working Paper 140 UK Treasury (2002)Google Scholar
- Graham, D.J., Glaister, S.: The demand for automobile fuel – a survey of elasticities. J. Transp. Econ. Policy
**36**(1), 1–26 (2002)Google Scholar - Grant-Muller, S.M., Mackie, P.J., Nellthorp, J., Pearman, A.D.: Economic appraisal of European transport projects: the state-of-the-art revisited. Transp. Rev.
**21**, 237–261 (2001)CrossRefGoogle Scholar - Hensher, D.A.: Integrating accident and travel delay externalities in an urban speed reduction context. Transp. Rev.
**26**(4), 521–534 (2006)CrossRefGoogle Scholar - Hickman, J., Hassel, D., Joumard, R., Samaras, Z., Sorenson, S.: Methodology for calculating transport emissions and energy consumption. TRL report, no PR/SE/491/98, Crowthorne, UK, and European Commission, DG VII-99, Luxembourg (1999). ISBN 92-828-6785-4Google Scholar
- Liu, L.N., McDonald, J.F.: Economic efficiency of second-best congestion pricing schemes in urban highway systems. Transp. Res.
**33B**, 157–188 (1999)CrossRefGoogle Scholar - Milne, D., Niskanen, E., Verhoef, E.: Operationalisation of marginal cost pricing within urban transport. AFFORD Deliverable 1. VATT Research Reports No 63. Helsinki (2000)Google Scholar
- Minken, H., Jonsson, D., Shepherd, S.P., Jarvi, T., May, A.D., Page, M., Pearman, A., Pfaffenbichler, P.C., Timms, P., Vold, A.: Developing sustainable urban land use and transport strategies – a methodological guidebook. Institute of Transport Economics, P.O.Box 6110 Etterstad, 0602 Oslo, Norway (2003)Google Scholar
- Newbery, D.M.: Road user charges in Britain. Econ. J.
**98**, 161–176 (1988)CrossRefGoogle Scholar - Peirson, J., Skinner, L., Vickerman, R.: The microeconomic analysis of the external costs of road accidents. Economica
**65**, 429–440 (1998)CrossRefGoogle Scholar - Pfaffenbichler, P., Shepherd, S.P.: A dynamic model to appraise strategic land-use and transport policies. Eur. J. Transp. Infrastruct. Res. Special Issue: Sustainable Transport.
**2**(3/4), 225–283 (2003)Google Scholar - Pigou, A.C.: The Economics of Welfare, 1st edn. Macmillan, London (1920)Google Scholar
- Proost, S., Van Dender, K.: The welfare impacts of alternative policies to address atmospheric pollution in urban road transport. J. Reg. Sci. Urban Econ.
**31**, 383–411 (2001)CrossRefGoogle Scholar - Rotemberg, J.J.: The efficiency of equilibrium traffic flows. J. Public Econ.
**26**, 191–205 (1985)CrossRefGoogle Scholar - Samaras, Z., Ntziachristos, L.: Average hot emission factors for passenger cars and light duty trucks. Thessaloniki, Laboratory of Applied Thermodynamics (LAT), Aristotele University of Thessaloniki (1998)Google Scholar
- Shefer, D.: Congestion, air pollution and road fatalities in urban areas. Accid. Anal. Prev.
**26**(4), 501–509. Elsevier Science Ltd. (1994)Google Scholar - Shefer, D., Rietveld, P.: Congestion and safety on highways: towards an analytical model. Urban Stud.
**34**(4), 679–692 (1997)CrossRefGoogle Scholar - Singh, R.: Improved speed-flow relationships: Application to transportation planning models. In: 7th TRB Conference on Application of Transport Planning Methods, Boston (1999)Google Scholar
- Small, K.A., Yan, J.: The value of “value pricing” of roads: second-best pricing and product differentiation. J. Urban Econ.
**49**, 310–336 (2001)CrossRefGoogle Scholar - Suzuki, T., Miyagi, T., Miyata, N.: A spatial examination of costs and benefits for urban transport users based on second best pricing systems. Paper presented to the 10th World Conference on Transport Research, Istanbul, July 2004Google Scholar
- Taylor, M.C., Lynam, D.A., Baruya, A.: The effects of drivers’ speed on the frequency of road accidents. TRL Report 421. TRL Limited, Old Wokingham Road, Crowthorne, UK (2000). ISSN 0968-4107Google Scholar
- Tinch, R.: Valuation of Environmental Externalities. UK Department of Transport, HMSO, London (1995)Google Scholar
- Transport Research Laboratory.: TRL Transport Policy Model User Manual. TRL, Crowthorne (2001)Google Scholar
- Van Vliet, D. SATURN – a modern assignment model. Traffic Eng. Control
**23**(10), 578–581 (1982)Google Scholar - Verhoef, E.T.: The Economics of regulating road transport. Edward Elgar Publishing Limited, Cheltenham (1996). ISBN 1858983649Google Scholar
- Verhoef, E.T.: Second-best congestion pricing in general networks: algorithms for finding second-best optimal toll levels and toll points. Discussion paper TI 2000-084/3, Tinbergen Institute, Amsterdam-Rotterdam (2000)Google Scholar
- Verhoef, E.T., Rouwendal, J.: A behavioural model of traffic congestion endogenizing speed choice, traffic safety and time losses. J. Urban Econ.
**56**(3), 408–434 (2004)CrossRefGoogle Scholar - Vold, A.: RETRO/IMREL A model for transport and land use planning in the greater Oslo area – version 1.0. TØI working report 1179/2000, Institute of transport Economics, Oslo (2000)Google Scholar