DOUBLE DECKER BUSES in AUCKLAND – RETROFITTING a CITY Fiona Tang and Remi Cruz (Auckland Transport)
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DOUBLE DECKER BUSES IN AUCKLAND – RETROFITTING A CITY Fiona Tang and Remi Cruz (Auckland Transport) Abstract To increase capacity on high demand bus routes and accommodate increasing public transport patronage, double decker buses are being rolled out in Auckland. As larger framed buses introduce new areas of risk to the road network, Auckland Transport (AT) assessed key bus routes and identified obstacles that required modification or removal to allow the safe passage of double decker buses. With no clear guidelines on the safe corridor envelope, AT worked from first principles and introduced new techniques. A measuring device that enables cost effective data capture was developed. To understand the effects of extreme bus manoeuvres on the front and tail swings, a trial road was built to simulate a double decker bus approaching and leaving a bus stop. This paper also discusses the challenges of retrofitting an existing road network involving multiple challenges and multiple stakeholders in addition to legal, environmental, and operational constraints to achieve the primary objective of providing safe corridors for double decker buses in Auckland. Key Words Auckland Transport, AT Code of Practice (ATCOP), double decker bus, public transport, verandas, lateral and vertical clearance Introduction 10.0%, 6.5% and 7.0% respectively. Auckland Transport (AT) is improving the bus Due to network constraints, single decker bus network throughout the Auckland region. Part services frequencies could no longer be of this effort is to increase capacity on bus increased without major reconfiguration of the routes operating at or near full capacity road corridors. The introduction of double including the Dominion Road route, Central decker buses, therefore, was the preferred Business District (CBD), and the Britomart strategy for increasing capacity on high Transport Centre. Before 2012, buses on demand routes and to accommodate the these routes were already running up to 95% increasing PT patronage over the next ten of their seated capacity during peak hours. years. The demand for public transport (PT) in Single decker buses permitted to operate in Auckland has been increasing and is projected the Auckland road network have a maximum to increase further, as reported in the dimension of 13.5m long, 2.5m wide Auckland Regional Land Transport Plan (excluding wing mirrors), and 3.1m high. (ARLTP), July 2015. Between 1994 and 2014, Proposed double decker buses have the same PT patronage more than doubled from 33 length and width but with a height of 4.25m. million trips to 72 million trips and is projected to double again in 2022. The ARLTP also AT assessed the impact of double decker bus reported that the bus services in the central operation on Auckland road network in 2012 bus corridors, Northern Express, and Botany by running a mock double decker bus on four to CBD routes experienced growth rates of key bus routes – the Northern Busway, Mount Eden, Sandringham, and Remuera. After this trial and minor tree pruning along Fanshawe Street, double decker buses were operated on the Northern Busway. The trial also established that the larger framed buses would introduce new areas of risk to the road network and identified obstacles that require modification or removal. Figure 2. Double decker bush crashed into a tree in South London injuring 32 people. Source:http://www.mirror.co.uk/news/uk- news/kennington-bus-crash-recap-after- 2945979 Figure 1. Double-decker bus wedged under canopy at Ipswich Hospital. Source: http://www.ipswichstar.co.uk/news/ipswich_do uble_decker_bus_wedged_under_canopy_at_i pswich_hospital_1_1382938 The initial trial was followed by a wider Figure 3. Double decker bus roof ripped off in assessment of 10 key routes shown in railway bridge accident. Source: Appendix 1 or about 200 kilometres of bus http://travel.aol.co.uk/2013/01/29/double- corridors. To ensure that the PT routes are decker-bus-roof-ripped-off-railway-bridge- safe for double decker buses and to justify the crash-hampshire/ cost of implementation within the next 10 years, AT explored different options and levels Corridor Clearance Assessment of mitigation. The cost of mitigation works was estimated at $24 million. An independent With no clear guidelines on the safe corridor economic evaluation by John Bolland envelope, AT reviewed double decker bus Consulting Ltd established that running double practices in the United Kingdom, focussing on decker buses on key routes would have safety issues. Accidents involving double significant economic benefits derived mainly decker buses show examples of hazards and from operational cost savings and traffic potential safety issues along the bus corridors benefits, outweighing the cost of mitigation in Auckland. In Figure 1, for example, a double works. decker bus crashed into the canopy of Ipswich Hospital injuring two passengers, an event highly likely to happen in the Auckland bus routes where verandas are more common. The maximum tail swing of the bus over the Similarly, the incident shown in Figure 2 is also kerb was 0.82m for the 12.6m fixed axle bus plausible due to the prevalence of roadside and 1.14m for the 13.5m rear steer bus. trees in Auckland. Consequences of bus drivers deviating from their designated routes Front swings were measured for buses are illustrated in Figure 3, an accident that can entering a bus stop or avoiding a hazard in a easily happen in Auckland due to driver’s general lane. When entering a bus stop, the error. Incidentally, to prove this point, a double maximum front swing of the bus overhanging decker bus crashed to a verandah on the kerb was recorded as 0.63m. When Symonds St early this year when the driver avoiding a hazard at a faster speed of about unloaded passengers on a taxi stand instead 30km/hr, the maximum front swing was of a designated bus stop. recorded as 0.46m. To further understand the hazards of operating Based on these trials, it was recommended double decker buses locally, accidents that clearances from kerb face of 0.8m on bus involving single decker buses in the Auckland stops and 0.5m on all other roads be adopted. region were analysed. From 2003 to 2012, The recommendations, however, did not take 2,431 reported incidents included 44 cases into consideration the potential impact of where buses left the carriageway or hit fixed extreme road camber and vehicle dynamic kerb-side objects. Forty-two of these incidents effects, such as body roll due to severe bus occurred on the routes being investigated for manoeuvres. AT commissioned TERNZ double decker bus use, and on 4 occasions, a Transport Research, an independent research bus mounted the kerb and struck a building. consultant specialising in transport related issues, to investigate further. As a result, As a bus turns, both of its ends rotate with the clearance of 1.0m from the kerb face on bus nearest axle acting as a pivot point. These are stops was recommended. commonly known as the front swing and the tail swing. The impact of a tail swing is typically To validate the recommendations and findings lower as buses pulling out from a bus stop is thus far, a 50m trial section of road with a 5% just starting to accelerate away from the kerb. cross-fall, the maximum allowed for sealed On the contrary, the front swing represents a roads in Auckland, was built to simulate a greater risk as a bus entering a bus stop is double decker bus approaching and leaving a decelerating from a higher speed toward the bus stop. The front and rear over swings of the kerb. bus were measured for different severe steering manoeuvres and the bus movements Prevailing Codes of Practices before ATCOP were tracked while it was in motion. A set of specified a lateral clearance of 0.5m over the robotic instruments capable of measuring footpath or road shoulder to allow buses to target prisms mounted on the left side of the manoeuvre safely close to the kerb. However, double decker bus was used, achieving an none were found specifically for double decker accuracy of within 10mm. buses and the required lateral clearance for bus stops. Hence, AT carried out trials using a These additional investigations resulted in the 12.6m fixed axle bus and a 13.5m rear steer revision of the lateral clearance on bus stops bus, which generates a larger tail swing than a from 0.8m to 1.0m measured from the kerb fixed axle bus. face. The 0.5m lateral clearance on all other roads remained. The tail swing of a bus turning out into the road from behind another parked bus was Height clearance was set at 4.6m to be investigated. Two options were tested: (i) with consistent with NZTA’s Road and Traffic the bus aligned a distance away from the kerb Guidelines RTS16: Guide to Heavy Vehicle in the manner recommended by driver trainers Management. Subsequently, however, height and (ii) with the bus wheels hard against the clearance for trees was increased to a kerb, considered poor practice but which minimum of 4.75m to allow for growth between occasionally occurs. pruning. Figure 4 below shows the lateral and height clearances adopted to provide a safe envelope along the double decker bus corridors. Figure 4. Lateral and height clearances for double decker bus safe corridors Figure 5. Measuring device for bus route surveys developed by Arborlab Consultancy In addition to the lateral and height clearance Services. requirements, AT determined that double greater detail in this paper as they are easily decker buses to be permitted in Auckland resolved through relocation. should have a maximum length of 12.6m and must be on fixed rear axles only.