The economic costs of road traffic congestion

Abstract

The main cause of road traffic congestion is that the volume of traffic is tooclose to the maximum capacity of a road or network. Congestion in the UK isworse than many, perhaps most, other European countries. More important, itis getting worse, year by year. Current official forecasts imply that congestionwill be substantially worse by the end of this decade, even on the veryfavourable assumption that all current Government projects and policies areimplemented in full, successfully, and to time. This is because road traffic isgrowing faster than road capacity. This is not a temporary problem: it willcontinue to be the case, in the absence of measures to reduce traffic, because itis infeasible to match a road programme to unrestricted trends in traffic growth.The effect, using the current Government method of measuring congestion,and a long established method of valuing it, would be that the widely quotedfigure of an annual cost of £20 billion, would increase to £30 billion by 2010.Under current social and economic frameworks, there are no feasible policiesthat could reduce congestion to zero in practice, or that would be worthwhiledoing in theory. But savings worth £4b-£6b a year could in principle be madeby congestion charging alone, over the whole network, of which (veryapproximately) half might be reflected in the prices of goods, and half insavings in individuals? own time spent travelling. A good proportion of thiscould alternatively be secured by an appropriate package of alternativemeasures: priority lanes and signalling; switching to other modes includingfreight to rail and passenger movements to public transport, walking andcycling; ?soft? policies to encourage reduced travel by car; land-use patternswhich reduce unnecessary travel; and associated measures to prevent benefitsfrom being eroded by induced travel. The combined effects of road chargingand a supportive set of complementary measures represent the best that couldbe reasonably achieved in the short to medium run. This could reducecongestion costs (as distinct from slowing down their increase) by 40%-50%.These broad-brush figures, though based on long-established methods, must betreated with great caution. The ?cost of congestion?, as used for thesecalculations, is based on relationships which in reality are not exact, stable oreven meaningful. The wrong indicator has been used, comparing average realspeeds with average ideal speeds. But in the real world, speeds are differentevery day, and so is the level of congestion. For just-in-time operation, and formuch personal and business travel, variability and reliability are much moreimportant. The really costly effect of congestion is not the slightly increasedaverage time, but the greater than average effect in particular locations andmarkets, and the greatly increased unreliability.During the near future, until road pricing is implemented, increases in roadcongestion can lead to some shift in the balance of attractiveness of rail freight,sufficient for a proportion of the freight market to transfer from road. Thiswould in turn make a small but significant contribution to reducing congestion,especially in some specific important corridors. Even though rail freight isusually a small proportion of all freight, the annual economic saving incongestion cost, to road users generally, from transferring a 5-times a week,200 mile round trip, mostly on congested motorways, from road to rail wouldbe in the order of £40,000 to £80,000, to which should be added thecommercial cost savings made by the freight operator who chooses to do so. Itshould be emphasised that sustaining this would require measures to preventinduced car traffic filling up the relieved road space.An example of the impact of factoring in unreliability is given by approximatecalculations made for journeys such as Glasgow to Newcastle, Cardiff toDover, or London to Manchester. In free-flow theory these could be 3-hourjourneys, but moderate congestion requires adding an hour to the average timeand another hour safety margin to ensure that a tight delivery slot is not missedtoo often. In congestion so severe as to double the average time, the extrasafety margin for unreliability could be as much as 4 hours, which is simply notfeasible in many cases.The ?total cost of congestion? is a large number, but it is practicallymeaningless and by ?devaluing the currency? it distracts attention from moreimportant, achievable, objectives. It would be better not to use it as a target forpolicy. The two key important things to do are:· Strategic action to reduce traffic volume to a level where conditions do notvary too much from day to day. In some circumstances this will slightlyincrease average speed, though not always: in some road conditions areduction of average speed can greatly improve the smoothness of trafficflow. But in both cases, it will greatly increase reliability, this being moreimportant than the change in average speed;· Practical measures to provide good alternatives for freight and passengermovements which reduce the intensity of use of scarce road space incongested conditions. Even where this only applies to a minority ofmovements, significant effects are possible.The Government plans to ?re-launch? the Ten Year Plan for Transport thisSummer or Autumn. It is not reasonable to expect that the re-launch willinclude congestion charging for cars within the decade, so it will need to planfor it as soon as possible after, and a short-term coping strategy of prioritymeasures to protect the most important classes of movement (both passengerand freight) from congestion in the period before charging is implemented