Traffic Reduction: Reallocating Roadspace and Its Impact on Traffic Levels, Exams of Construction

Download Traffic Reduction: Reallocating Roadspace and Its Impact on Traffic Levels and more Exams Construction in PDF only on Docsity! Disappearing traffic? The story so far S. Cairns, S. Atkins and P. Goodwin Reallocating roadspace from general traffic, to improve conditions for pedestrians or cyclists or buses or on-street light rail or other high-occupancy vehicles, is often pre- dicted to cause major traffic problems on neighbouring streets. This paper reports on two phases of research, resulting in the examination of over 70 case studies of roadspace reallocation from eleven countries, and the collation of opinions from over 200 transport professionals worldwide. The findings suggest that predictions of traffic problems are often unnecessarily alarmist, and that, given appropriate local circumstances, significant reductions in overall traffic levels can occur, with people making a far wider range of behavioural responses than has tradition- ally been assumed. Follow-up work has also highlighted the importance of managing how schemes are perceived by the public and reported in the media, with various lessons for avoiding problems. Finally, the findings high- light that well-designed schemes to reallocate roadspace can often contribute to a multiplicity of different policy aims and objectives. 1. INTRODUCTION Reducing roadspace for general traffic, and reallocating it to pedestrians or cyclists or buses or trams or other high- occupancy vehicles, could significantly increase the attractive- ness of these modes, and facilitate more efficient use of the road network. Yet proposals for such changes are usually controversial. One recurrent issue is whether the displaced traffic will simply divert to neighbouring streets, clogging them up and leading to worse congestion and pollution. This paper reports on findings from research based on over 70 case studies from eleven countries, and the opinions of over 200 transport professionals worldwide. The findings suggest that such prob- lems are, in reality, rarely as bad as predicted, and that, with careful planning and appropriate implementation, reallocating roadspace to more sustainable modes of transport can result in a variety of complementary benefits. 2. CONTEXT In the mid-1990s, there was a radical shift in UK Government policy on road building. Specifically, the Government clarified that building roads was not always a solution to congestion, as creating new capacity could generate traffic. This was partly due to technical advice from its own Standing Advisory Committee on Trunk Road Assessment (SACTRA),1 and partly due to the popular recognition that, for example, building the M25 motorway had not produced consistently free-flowing traffic conditions around London (despite having been built with excessive spare capacity according to the traffic conditions before its construction). However, while it was officially recognised that building roads could induce additional traffic, the opposite proposition, namely that reducing roadspace could reduce traffic, was not widely accepted in either theory or practice. Consequently, numerous proposals for pedestrianisation or bus priority schemes were rejected, due to fears of the problems that they could create on surrounding streets. Examples in London include schemes in the London ‘Green Areas’ study, and parts of the London Bus Priority Initiative such as the whole route priority proposed for Route 68 between Camden and Camber- well. To address the issue, a research study was commissioned by London Transport and the Department of the Environment, Transport and the Regions in 1997. Two reports were published—by Cairns, Hass-Klau and Goodwin on the practical evidence,2 and by MVA3 on the implications for modelling. This paper summarises and updates the evidence study. 3. THEORIGINAL STUDY The original evidence study (by Cairns, Hass-Klau and Good- win) sought to identify all possible case studies of circum- stances where roadspace had been reallocated, whether due to positively planned schemes, temporary road closures for main- tenance or renewal of transport facilities, or natural disasters. Although the stimulus for change varied, in each case drivers needed to decide what to do when their normal travel patterns were disrupted, and there were useful insights from all the examples as to how they reacted. Examples included pedestrianisation schemes in German and other Continental European cities; the City of London ‘Ring of Steel’ project following IRA bombing; closures of bridges such as London’s Westminster Bridge, Tower Bridge and Hammer- smith Bridge for repairs and maintenance; city-centre traffic schemes in places like Oxford, Cambridge and Wolverhampton; the introduction of bus lanes in cities such as Cardiff, Bristol and Toronto; the closure of a rural road south of London; the street enhancement projects in Norwegian towns; the Six Towns Bypasses Monitoring Project; the Tasman Bridge collapse in Hobart, Australia; and the effects of earthquakes in Proceedings of the Institution of Civil Engineers Municipal Engineer 151 March 2002 Issue 1 Pages 13^22 Paper 12772 Received 06/11/2001 Accepted 06/12/2001 Keywords: town & city planning/transport planning/urban environment Sally Cairns Research Fellow, ESRC Transport Studies Unit, University College London Stephen Atkins Visiting Professor, University of Southampton Phil Goodwin Professor of Transport Policy and Director of the ESRC Transport Studies Unit, University College London Municipal Engineer 151Issue1 Roadspace reallocation schemes Cairns et al. 13 Kobe, Japan, and in California, USA, where transport links were suddenly and unexpectedly removed from the network. Altogether, evidence from over 200 transport professionals and about 150 published documents was collated to provide information on about 100 case studies from across the world. About 60 provided sufficiently detailed evidence for in-depth analytical review. The key findings were as follows. (a) When roadspace for cars is reallocated, traffic problems are usually far less serious than predicted. (b) Overall traffic levels can reduce by significant amounts. (c) Traffic reduction is partly explained by recognising that people react to a change in road conditions in much more complex ways than has traditionally been assumed in traffic models. 4. FOLLOW-UP RESEARCH Following the original study, additional innovative schemes of roadspace reallocation have been implemented in practice and further research has been carried out. In February 2000, a conference was promoted by Landor Conferences to discuss further experience.4 The European Commission, DG Environ- ment, has commissioned a handbook entitled Traffic Evapora- tion in Urban Areas, which should become available soon. Meanwhile, the researchers at University College London have undertaken two main follow-up exercises. (a) An analysis of twelve further UK case studies.5 This includes an investigation of the M4 bus lane, changes to central Oxford and Cambridge, the Leeds high-occupancy vehicle lane, the Gloucester Safer City project and the redesign of Vauxhall Cross (a major gyratory system in south London). (b) An opinion survey was sent to approximately 400 transport professionals who work on roadspace reallocation issues, or who purchased the original research study. A total of 142 responses were received from a wide range of organisations in different countries. (Some tendency for a self-selection bias was probably inevitable.) This was complemented with a qualitative survey of delegates attending the Landor Conference in 2000, and extensive correspondence with transport professionals, following from the original research study and from a request in Local Transport Today, asking for reports of further experience.6 One point, which is continuously stressed, is that every scheme to reallocate roadspace is different, and so the effects of any plan will be highly dependent on individual circumstances. This is undoubtedly true and was emphasised in all the original research work. However, while in theory, many people recognise that the effects of a scheme ‘depend on the circumstances’, it is reported that, in practice, many work on the basis that traffic levels remain fixed. As one respondent put it, the assumption is that ‘nothing will make people get out of their cars—they’ll always try and find another way round, and, if necessary, they’ll just sit and wait in the traffic’. For future transport policy, it is critical to clarify whether this assumption is correct. 5. PERCEPTIONS OF TRAFFIC IMPACTS The first main finding of the original study was that traffic conditions following a scheme are rarely as bad as expected. Typically, local papers run headlines warning of ‘traffic chaos’ in advance of schemes. The closure of Hammersmith Bridge in 1997, for example, was expected to bring most of south-west London to a standstill. Yet, those who have implemented schemes rarely report that such consequences result. Instead, typical comments are of the form: ‘a lot of the traffic seems to have disappeared, and we don’t know where it has gone’. There are reports of short-term ‘traffic chaos’: where congestion was previously bad, it often stays bad; and there can be increasing problems on particular local streets. (This can be a particular problem where such streets are outside the boundary of the local authority implementing the scheme.) However, wide- spread, long-term disruption is hardly ever reported. This finding appears to be robust. To date, the research work has only identified two schemes that have been withdrawn— the introduction of a bus lane in Dunstable (in 1999) and the trial closure of Orpington High Street (in 1996). The closure of Orpington High Street was reversed because there were prob- lems with enforcement, and retailers were not convinced of the benefits. However, alternative means of improving local accessibility to the high street for pedestrians, and other priority groups, are being explored. In the case of Dunstable, some problems with scheme engineering, and an unfortunate combination of circumstances when the bus lane opened, meant that there were significant initial problems which made it politically undesirable to continue with the scheme. The other scheme that should be mentioned is Hammersmith Bridge, London, which was reopened to general traffic in 1999. However, this was never closed as part of a planned policy, and the decision to reopen it was mainly based on a public opinion survey rather than a technical assessment of the traffic conditions. (The importance of managing public opinion is discussed further below.) These examples compare with over 40 cases of planned schemes that have been successfully imple- mented and are still in place. The survey of professional opinion confirms this experience. Over 90% of respondents knew of a roadspace reallocation scheme which had ‘apparently’ or ‘definitely’ been implemented ‘without causing any significant problems for general traffic’. However, less than a quarter had heard of a scheme that had apparently led to long-term traffic problems, and only 7% were definite that there were such cases. Hence, current experience suggests that it is rare that roadspace reallocation schemes cause substantial and unacceptable levels of congestion and disruption. Of course, in the past, it is only the better-planned schemes that will have been accepted and implemented. It cannot be asserted that every proposal for giving more roadspace to buses, cyclists or pedestrians will be problem-free. However, the findings should provide reassurance for those investigating such options, and suggest that decision- makers can perhaps afford to be less conservative than they are at present. Controversy, however, is not always dispersed by technical success. Experience from schemes like the M4 bus lane, and the Oxford Transport Strategy, coupled with the problems identified in Orpington and Dunstable, highlight the importance of getting the details of scheme implementation right, and also of 14 Municipal Engineer 151Issue 1 Roadspace reallocation schemes Cairns et al. Description Vehicle flows Vehicle flows on Traffic on altered route/area parallel/alternative routes change Before (A) After (B) Before (C) After (D) (E) Nurnberg Rathausplatz 1988^1993 (5 years) 24584 0 67284 55824 7146˝6 * Wiesbaden city centre and boundary 1990^1992 1303 366 8445 7968 7108˝5 * Southampton city centre 1996^2000 5316 3081 26522 24104 787˝5 * Nurnberg Rathausplatz 1988^1989 (1 year) 24584 0 67284 70692 786˝1 * Tower Bridge closure 1993 (1 month) 44242 0 103262 111999 780˝3 Partingdale Lane local area 1997 (6 months) 988 18 2519 2735 776˝3 Rotherhithe Tunnel closure 1998 (1 month) 40000 0 245381 260299 762˝7 Hobart: Tasman Bridge collapse (14 months) 43930 0 761˝3 Orpington High Street closure 1996 (3 months) 1105 760 7084 6847 752˝7 * Bologna city centre 1981^1989 177000 87000 750˝8 * Hanshin-Awaji earthquake 1995 (after highways restored) 252900 103300 205900 233600 748˝2 Gothenburg CBD 1970^1980 150000 81000 746˝0 * New York highway closure 1973 (2 years) 110000 50000 540000 560000 745˝5 Edmonton^Kinnaird Bridge closure 1979 (3 weeks) 1300 0 2130 2885 741˝9 New York highway closure 1973 (1 year) 110000 50000 540000 560000 736˝4 Hammersmith Bridge 1997Elocal area only (1 month) 30698 3000 104698 122106 733˝5 A13 closure, 8 June 1996 (same day) 56000 22800 50800 65513 733˝0 Partingdale Lane local area 1997 (3 months) 988 21 2519 3190 730˝0 A13 closure, 1 June 1996 (same day) 56000 19722 50800 71463 727˝9 Oxford Street 1972E1st phase 1800 950 4050 4400 727˝8 * Ring of Steel ‘central core’ 1992^1994 160000 120000 725˝0 * A13 closure, 15 June 1996 (same day) 54200 26804 52200 67347 722˝6 Aarau 1988^1994 (evening peak traffic) 1444 1132 2275 2301 719˝8 Oxford Transport Strategy 1999 (12 months) 57186 46773 718˝2 * Hamm 1991 21500 18000 716˝3 * York: Lendal Bridge closure 1978^1979 (1 month) 16290 0 49100 62800 715˝9 Luneberg 1991^1994 106002 90597 714˝5 * Wolverhampton 1990^1996 (within ring road) 81500 69750 714˝4 * Hobart 1975: Tasman Bridge restored 5 months 43930 714˝0 Bologna city centre 1972^1974 213200 185500 713˝0 * Leeds HOV 1998 (1 month) 3384 2779 10824 11069 710˝6 CambridgeEBridge Street closure 1997 (5 months) 23411 20931 710˝6 * Oxford bus lanes 1974^1975 (1 year) 60684 54820 79˝7 # Cambridge Core Traffic Scheme 1996^2000 (4 years) 76155 69792 78˝4 * Loma Prieta earthquake 1989 (after restoration) 245000 77˝5 A104 Bridge Road bus lane 1994 (1 year) 34070 31102 81609 82121 77˝2 # Freiburg ring road 1996^1997 (10 months) 34200 22600 64500 73700 77˝0 * Oxford city centre 1974^1984 (10 years) 60684 56599 76˝7 York bus lane (7 weeksE50% signal capacity) 681 650 600 594 75˝4 # York bus lane (1 weekE67% signal capacity) 681 645 600 606 74˝4 # Cardiff bus lanes 1993^1996 156299 149596 74˝3 # Gothenburg central urban area 1975^1980 320000 307200 74˝0 * Leicester ring roadEam peak 1999 (2 months) 4575 3972 6059 6511 73˝3 EdinburghEPrinces Street closure 1997 (3 months) 221953 215011 73˝1 * M4 bus lane 1999 (1 year) 52800 51300 72˝8 # Northridge earthquake 1994 (after restoration) 698000 670000 71˝7 Nottingham traffic collar 1975^1976 (9 months) 13380 13150 71˝7 Wolverhampton 1990^1996 222900 220300 71˝2 * CambridgeEEmmanuel road closure 1999 (7 months) 70030 69792 70˝3 * Ring of Steel ‘Square Mile’ 1992^1994 (1 year) 254192 253613 70˝2 * EdinburghEPrinces Street closure 1997 (1 year) 221953 221834 70˝1 * Munich bridge closure 1988 32000 0 71000 103000 0˝0 Vauxhall Cross area 1999 (3 months) 537543 539704 0˝4 Orpington High Street closure 1996 (1 year) 1105 744 7084 7461 1˝4 * Frankfurt am Main bridge closure 1989 29500 0 162500 192500 1˝7 Westminster Bridge 1994^1995 41739 41284 90276 91626 2˝1 M4 bus lane 1999 (2 months) 52800 54000 2˝3 # CambridgeEBridge Street closure 1997 (2 months) 31869 28781 44286 48338 3˝0 * NorwayEStreet enhancement 1991^1995 15300 15800 3˝3 * Leicester ring roadEam peak period 1999 (2 months) 10935 11212 7542 7918 6˝0 Aarau 1988^1994 (24 h traffic) 18292 17244 26512 30093 13˝8 Six Towns Bypass Project (1992^1995) 38212 30968 51697 66808 20˝6 Leeds HOV 1998 (13 months) 3384 3438 10824 11634 25˝5 Where the third and fourth columns are shaded, traffic has usually been counted crossing a cordon around an area-wide scheme (typically a town centre), such that there are no ‘alternative routes’ into the affected area. Dates refer to scheme dates. Monitoring period after scheme opening is given in brackets. *=town centre scheme; #=bus lane. Table 1. Recorded changes in traffic levels for individual case studies Municipal Engineer 151Issue1 Roadspace reallocation schemes Cairns et al. 17 Nurnberg and Wiesbaden, where more traffic disappeared from the networks as a whole than previously used the particular roads that were closed. In these cases, the specific changes implemented have formed part of a wider programme of measures, which have had a cumulative effect on how people choose to access the city. As a cross-check on the credibility of the case study evidence, professionals were asked what they would consider to be an appropriate assumption for traffic changes following a road- space reallocation in their area. About two-thirds were not prepared to comment, either because they did not know or because they felt it was inappropriate to generalise. However, a third were prepared to give an opinion and the results are shown in Fig. 2. Averaged out, these suggest that professionals think that an 11% traffic reduction might be achieved by a general roadspace reallocation scheme in their area (Fig. 2(a)), and an 8·8% traffic reduction might be achieved by intro- duction of a bus lane (Fig. 2(b)). It is notable that only 3% of professionals said that they thought the most appropriate assumption would be zero traffic reduction for either general roadspace reallocation or the introduction of a bus lane in their area. Hence, the case study results suggest that traffic reduction is a real phenomenon, and that the levels of traffic reduction that occur from reallocating roadspace can be quite high. Most transport professionals support the concept of traffic reduction and their opinion of its impact is broadly in line with the collective results from the monitored studies. In particular, both sources highlight that, when implementing roadspace realloca- tion schemes, the most appropriate assumption is not usually that traffic levels will remain fixed. However, both sources also highlight the variability of results and the importance of the context in which policies are implemented. Consequently, those involved in schemes will always need to consider local circumstances, and comparable experience elsewhere. To this end, website databases of examples—such as www.eltis.org— are of value, and a specific compendium of places that have reduced roadspace for general traffic could be an important resource. The original study report2 and the update of case studies5 may provide some useful information of this nature for practitioners. 7. EXPLAINING TRAFFIC REDUCTION The final finding from the original study was that the reason traffic reduction is observed is that the behavioural responses that people make following a change in road conditions are much more complex than has previously been assumed, or allowed for in traditional transport modelling. A three-level model of behaviour was developed. (a) At the first level, there is the perception that road capacity for general traffic has been reduced. However, any changes are offset, or more than offset, by capacity increases on other routes, or changes in traffic management, or changes in driving style, which pack more vehicles into the same space. In other words, not all examples of roadspace reallocation reduce road capacity. For example, during the Nottingham Zones and Collar experiment in 1975–1976,15 it was reported that more cars were getting through the traffic-lights on the approach roads to the centre, even though the green times allocated were shorter, presumably because drivers were sitting waiting, with their foot on the accelerator, ready to leap off the lights as soon as possible. Mean: Median: –21·9% –10·6% Percentage change in traffic for individual case studies –200 –150 –100 –50 0 50 Fig. 1. Distribution of recorded changes in traffic levels for individual case studies 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 (a) (b) 0 5 10 15 20 25 30 Estimated percentage change in traffic Estimated percentage change in traffic Average: –11·0% Average: –8·8% Fig. 2. Number of respondents giving estimates about the likely impact on traffic levels of: (a) a general roadspace reallocation; and (b) a bus lane 18 Municipal Engineer 151Issue 1 Roadspace reallocation schemes Cairns et al. (b) Second, there may be a real reduction in capacity on the treated road or area, but this may be offset by adequate spare capacity on alternative routes or at other times of the day. Consequently, people may change their route or journey time, but the overall number of trips and vehicle mileage is likely to remain relatively unchanged. This appears to have been the case following changes to the west side of the ring road in Leicester,16 where traffic has reduced in the peak hour, but there have been compensat- ing traffic increases in the shoulders of the peak and on the eastern side of the ring road. (c) The third situation is where there is not adequate additional capacity on other routes, or at other times, either due to the nature of the network, the prevailing level of congestion or the comprehensiveness of the scheme. In these circum- stances, as well as rerouteing or retiming their trips, a wide range of other responses were reported in surveys. These included people changing their mode of travel, choosing to visit alternative destinations, changing the frequency of their journey, consolidating trips for different purposes, altering the allocation of tasks within a household to enable more efficient trip-making, car-sharing, or no longer making journeys (e.g. by working from home occasionally). Longer-term responses included changes in job location, changes in household location and changes in developers’ choice of location for new development. These responses differed from individual to individual and from place to place. It is these cases where conventional assumptions about behavioural change are likely to be most inappropriate. In understanding how such complex reactions can result from a change in road con- ditions, the study highlighted that many of these changes are being made all the time anyway, for other reasons. Underlying aggregate traffic patterns, there is a complex ‘churn’ of individual turn- over. Hence, for example, surveys of number-plates have shown that as many as 50% of cars on a major commuter route on two sub- sequent days can be different, even though overall traffic levels remain similar.17 This means that when road con- ditions change, a range of travellers are affected. Some are people who are used to making a particular journey in the same way every day, who are likely to be relatively resistant to changing their behaviour. However, many others will in any event be making a mixture of minor and major changes to their journey patterns. Hence, a roadspace reallocation may simply tip the balance in a decision that is being made for other reasons. For example, people moving job or moving house are very unlikely to do so solely because the roads change. However, if they are doing so anyway, it may be a factor in when and where they choose to relocate. It also means that some travellers are affected who have little prior experience of using the route at the time chosen. They will have limited expectations of what journey times or conditions might be, and their behaviour will be conditioned by their new experience, rather than any past history. Consequently, they may be more amenable to changing travel behaviour, as they will make their travel arrangements without preconceptions. The range of potential responses identified was drawn from individual case study reports. As a cross-check, transport professionals were asked which of these responses they thought were credible changes that some people would make following a significant roadspace reallocation. The results on short-term responses are shown in Fig. 3. Clearly, the responses which are conventionally recognised in transport planning, such as changing the route or mode of the journey, also receive the greatest support from professionals as being plausible changes that people make. As responses become less commonly considered in transport planning, there is less agreement that people are likely to make such changes, but there is also greater uncertainty, with more professionals saying that they simply ‘don’t know’. Significantly, all the responses listed get at least 30% of professionals saying that they think some people would make those changes, and over 55% saying that people would either normally make such changes or might do so in 0% 20% 40% 60% 80% 100% Yes No Could a significant roadspace reallocation result in some people changing... The route of a journey When they travel Their means of travelling How often they make a journey What is done on one trip A journey destination The driving style Whether they car-share Who does certain jobs within their household Yes (in exceptional circumstances) Don't know Fig. 3. Professional opinions about plausible behavioural responses to a change in road conditions Municipal Engineer 151Issue1 Roadspace reallocation schemes Cairns et al. 19