Claverton Conference 24/26 th October SUSTAINABLE LIGHT RAIL By Prof. Lewis Lesley

Transcription

1 Claverton Conference 24/26 th October 2008 SUSTAINABLE LIGHT RAIL By Prof. Lewis Lesley SUMMARY In an increasingly urbanized world most personal journeys are made in towns and cities and are relatively short, in UK 75% under 8km long. In the developed world, the motorcar dominates these trips. Car drivers will however transfer some trips to rail. Electrically powered light rail (or tramway) is an economic means for satisfying many short urban trips. Light rail can be constructed with a minimum of urban disruption and when coupled with renewable generation is energy sustainable. It also has a much smaller carbon footprint, when diverted car trips are included, than any other mode except bicycles. 1.0 Definitions Light rail is a passenger transport system using steel rails to support and guide electrically power vehicles, running on street with other traffic and on separate dedicated lines. Normally light rail is driven on sight without railway signaling, so it can share road space or road alignments, and mix safely with road vehicles. Ideally light rail should enjoy 100% priority over other traffic, through dedicated lanes and the pre-emption of traffic lights. Sustainable light rail emits no CO 2 in the operating cycle, using renewable generation. When attracted car trips are included, light rail reduces total CO 2 emissions. It is also financially viable so not vulnerable to public spending squeezes. Consistent market research and experience over the last 50 years in Europe and North America shows that car commuters are willing to transfer some trips to rail based public transport but not to buses. Typically light rail systems attract between 30 and 40% of their patronage from former car trips. Rapid transit bus systems attract less than 5% of trips from cars, less than the variability of traffic. 2.0 Unsustainable energy and transport The present UK energy consumption mix and its growth, is based on increasing use of fossil fuels. Not only are these fuels, and in the case of transport use, very dependent on oil, which is expected to peak in production soonest compared to other fossil fuels. As importantly whilst stationary users of oil can convert to other fuels and indeed to renewable energy sources, most transport, especially road transport has no obvious alternative power system which can be economically implemented. 1

2 Fig. 1 It should be noted that whilst total energy use over this period has been nearly static, solid fuel use has decline gas increased, and oil has been static as the decline in the use of oil for electricity generation, has been matched by the growth of (road) transport use. Fig. 2 Change in energy mix 1990 to 2001 Fig. 3. Energy end users 1990 to 2001 Transport energy consumption is almost equal to oil consumption. 2

3 Fig. 4 Growth of transport energy use Road and air travel are almost entirely responsible for the growth of energy consumption in the sector. Fig. 5 Modal use of energy in road transport In road transport, nearly two thirds of energy use is for private cars, with goods vehicles accounting for another third, leaving all other modes of road transport using only 3%. 3

4 Fig. 6 Consumption of transport services Considering the use made of different modes of passenger transport, the dominant is private car, accounting for about 800bn passenger km. pa. The next are an order of magnitude less, bus and rail, each with about 80bn passenger km. It is worth noting that rail has increased slightly over a 30 year period, whilst bus use has declined by iver 10%. Air has grown from the least mode in 1970 to the fourth used mode at about 10bn passenger km pa, with motor and pedal bikes being about 6bn km pa. Fig. 7 Transport greenhouse gas emissions 4

5 Fig. 7 shows air transport as the most serious greenhouse gas emitter because the Department for Transport has failed to include private car use, which would be an order of magnitude off the scale about 500million tones pa, and is the main reason the UK will fail to hit its EU emission targets, without a serious effort yo divert car trips to less polluting modes. Fig. 8 Public transport greenhouse gas emissions In comparison to the other modes of transport, the greenhouse gas emissions from public transport are trivial. This comes out more clearly in Table 1. Table 1. Transport % of UK Greenhouse gas emissions Emitter All Transport Public Transport UK Total %Transport 15% 17% 18% 19% 20% 21% 22% 21% 22% Whilst transport in both absolute and relative terms represents a growing greenhouse emitter, public transport modes have been reducing emissions in absolute terms, representing only 4% of all transport greenhouse gases. Considering in detail how private cars are used (Fig. 9), shows that most trips are short, and that less than 3% of all trips made are over 50km long. The potential is therefore great for switching short car trips to better public transport (or cycling), where the journey time differences are small. 5

6 Fig. 9 Trip length distribution of car travel. 75% of trips < 8km 50% < 5km 25% < 2km 3% > 50km The data presented in this section shows that transport is a large and growing consumer of fossil fuel, that transport is highly dependent on (imported) oil, and that transport is a growing emitter of greenhouse gases. For passenger travel, the car is the dominant mode and emitter of greenhouse gas, but the majority of car trips are short. Such short trips can be attracted to better public transport. Can market research provide a guide? Throughout the industrial world, car drivers are willing and do switch to rail. An insignificant number are willing to switch to buses. The reasons for this reflect perceptions and experience of service speed, reliability, travel comfort and social acceptability. Historically Metros have been seen as the way to give metropolitan areas high quality rail systems. Light rail however has been shown to give about 90% of the benefits of Metro at about 10% of the investment cost. This is particularly so when traffic management measures are implemented to give light rail priority and reduce the available road capacity for private car use. 3.0 Modal shift to light rail It follows that light rail lines should be built parallel to the busiest roads, with the highest volumes of car traffic. Only by diverting car trips will light rail reduce urban greenhouse gas and pollution. Building light rail to serve areas of low car ownership or high unemployment will rarely make significant ecological 6

7 contributions. People drive cars for among other reasons their convenience, speed and dependability. Despite the rising cost of fuel, cost is rarely the most important factor in car use. Using taxis is usually cheaper than having a car. For light rail to achieve significant market penetration, journeys must be fast, waiting times short and operations 100% reliable. As a rule of thumb people will not wait for longer than the ride time, since it would usually be faster to walk. For short urban trips of under 10mins, the service interval needs to be less than 10 minutes, ideally about 5 minutes, giving an average wait of less than 3 minutes. A no timetable, convenient, turn up and go service is the first requirement to attract committed car users. Fast journeys need direct routes and high operating speeds. Light rail service speeds should be above 25km/hr. Here there is an interaction with stop spacing. Closer stations mean shorter walks but a slower operating speed. Widely spaced stations mean longer walks but a faster speed. The local population density will determine the optimum stop spacing, to minimise overall journey times, and give a competitive alternative to car use. This optimum will also maximise catchments and hence patronage, and depending on fares, revenue. Park and ride is vital both for maximising the attraction of external car trips, reducing traffic and raising patronage. The factors on the siting of park and ride stations are well determined and proven in practice. The terminals of tram lines make good park and ride stations, since there will usually be a tram waiting to depart, which is important in maintaining passenger confidence. Such terminals will be sited either on the edge or slightly out of town. This would make the installation of wind generators acceptable, and provide renewable power. 4.0 R & D for sustainable tramways Tramways have developed incrementally over the last 150 years. Recently the trend has been to use modified heavy rail technology, which has increased costs and the weight of trams. This paper concentrates on vehicle technology, although other aspects of tramways have also been addressed to reduce costs or improve performance, especially track and power supply systems. The increase in weight per passenger space has been noticeable in the last 20 years. Contemporary trams have masses of about 200kg per passenger, compared to 125kg for buses. 7

8 Table 2 Comparison of vehicle weight per passenger Type of Public Transport Unladen kg No. of passengers Kg per passenger Bus Single deck rigid Double deck Articulated Trolleybus Train Metro car (electric) Suburban (diesel) Tram Tatra T5C Manchester Metrolink Sheffield Supertram City Class After Lesley 1994 With frequent start and stops of urban operations, most of the energy used is due to mass and maximum speed. Kinetic Energy = 0.5mv 2 equ. 1 The two critical variables in urban transit energy use are vehicle mass and the maximum speed. Many designers have tried to capture braking energy to reduce overall consumption. Electrical regeneration into batteries or back to the power grid, or mechanically, e.g. into flywheels, have produced at best 25% power reductions, ignoring any weight penalties from this equipment. Halving the tram weight will automatically halve power consumption. Reducing the maximum speed can be achieved by optimising stop spacing and using the maximum rate of acceleration that is ergonomically safe for standing passengers. Most trams accelerate at about 1.0m/s 2. Trams that can accelerate at 1.8m/s 2, on a 400m stop spacing, can reduce the maximum speed needed by 3%, to achieve the same operating speed. A 3% lower maximum speed means 6% less energy used per start stop cycle. Historically trams had steel under frames and wooden bodies for a low mass. Learning from the automotive and air industries, all metal integral bodies can have the same mass per passenger space as wood but be much stronger and safer. 8

9 Although low voltage dc power systems still supply tramways, the operating voltages have increased from 500 to 750. This means that the current used has not increased in line with tram weights, since W = IV equ.2 Increasing the voltage by 50% means the current has only increased by 33% for trams twice as heavy. Nevertheless a contemporary 40 tonne tram will draw about 1400amps when accelerating. This creates a large voltage drop between the tram and substation, reducing performance, and to increase the number of trams operating means strengthening the substations and power distribution. Originally trams were powered by dc motors using variable resistors (rheostats) for acceleration, another source of energy wastage in heating resistances. More recently power transistors were used to chop the dc voltage, to give variable voltages and so vary motor speed. Today most trams use ac motors powered by variable frequency and variable current inverters, fed from the dc Overhead Line (OHL). The market for tramcars is limited, with a world production of less than 1000 annually. In comparison over 100,000 buses are built annually, so can afford to invest in product development, and in comparison to trams be more technically innovative. This is compounded by the replacement cycle for buses being typically 10 years, and 30 years for trams (70 in Blackpool). In comparison to private cars, trams appear obsolete long before they are worn out. Fig. 10 Tram still running in Blackpool after 100 years 9

10 Even at the most optimistic levels of investment in new tramways, the vehicle volumes will not be large enough to support mass production, the usual way to reduce unit costs. The TRAM research project begun in 1988 has turned this logic around by identifying mass produced components off the shelf (COTS) from other industries, that can be used unmodified on trams. The challenging part has been to manage the interface between different standard components, and the rail environment, which in some aspects is kind and in others harsh. The R&D process began with simulations and calculations, progressed to bench and laboratory testing, then the construction of a slave vehicle using a redundant 1930!s tram in Blackpool. Finally a full size prototype vehicle was built and tested in Blackpool. From that experience, the tram was rebuilt, re-equipped with the next generation COTS and tested in Birkenhead and Blackpool. Fig. 11 Slave tram being fitted out at Carnforth Depot One of the advantages of COTS is that the original equipment manufacturers (OEM) are engaged in constant product improvement. This means the tram builder can piggyback on that to achieve more advanced vehicles with a minimum of investment. As an example the power train COTS used on the City Class tram has a high level of energy efficiency, and continuous power optimisation to reflect varying vehicle loads and track conditions. In overall terms, the power train is better than 90% efficient. 10

11 Fig. 12 Prototype tram at Fleetwood on clearance tests A team from the Electrical Engineering Dept. of the University of Manchester measured power consumption and compared it with other contemporary trams. (TABLE 1). This found the city class uses significantly less than similar capacity and performance trams, and less even that smaller, lighter but older trams in Blackpool. Part of the reason for the higher energy efficiency is of course lower vehicle mass, and part through the advanced power electronic COTS. Table 3 Power consumption of various tramcars Tram type Weight (tonnes) Power use (kwh/km) Blackpool Centenary Manchester Metrolink Croydon Tramlink Sheffield Supertram City Class

12 Fig.13 Prototype at Blackpool Pleasure Beach Application projects How do new capital technologies get introduced when the market is dominated by the public sector, where a minimum of three previous satisfied customers are needed? We might reflect how quickly mobile phones would have been introduced in Britain, if telecoms was still a monopoly of the GPO? This Catch 22 can be broken by private sector initiatives, where the risk is taken by the investors, who then get the rewards from commercial projects. Changing the fundamental economics of tramway projects, away from a subsidised public sector controlled environment is however the subject of another paper? Suffice it to say that privately funded projects are being progressed, which will enable the rate of new tramway projects in the UK to increase from the average of one every 4 years achieved over the last 20 years of public funding, to several a year. It might thus be possible to catch up with German levels of tramway provision in 20 years, rather than 150. Several of these privately funded projects are linked to complementary renewable power generation, making the tramways energy self sufficient, zero CO 2 and when attracted car trips are factored in, a net reduction of urban CO 2. 12

13 Fig. 14 Coping with steep hills and tight curves in Birkenhead 6.0 Conclusion To reduce CO 2 in urban travel, significant numbers of car trips must be attracted to public transport (or cycling?). Buses have not been able to achieve that, and also need imported fuels that add to CO 2 and other health threatening emissions. Tramways are proven worldwide to attract up to 50% of their patronage from car users. Technical R&D to improve the efficiency of trams, with the adoption of COTS to reduce costs, makes new tramways CO 2 reducing and give value for money. With the reduction of the cost of Photo Voltaics, and better power density batteries or super capacitors, the roof of a tram is big enough to be the renewable power generator, not needing any other power supply. That however is the subject of another paper, and the technology is some way in the future. 13

14 Fig. 15 New city class tram nearing completion at Blackburn factory 2008 References Lesley.L, Winstanley. A, Renfrew. A, Barnes.M and Chymera. M Power Consumption in a new LRV Railway Engineering June 2007, ISBN Lesley.L, City Class LRV, The Rail Engineer No. 27, Jan 2007 Lesley. L Affordable Mass Transit? Mass Transiot, Washington DC, Feb 2005 Lesley. L Contributor Improving public transport in England through light rail, National Audit Office. 19 th April

15 Lesley. L, Light rail value for money? Report to National Audit Office. Feb 2003 Lesley. L The role of rail in European public transport. PTIU Seminar, Shire Hall Mold, 6 th Dec Lesley. L Progress with the TRAM low weight LRV Light Rail 94 Conference 8-10 November 1994 Proceedings Published by Transport Science Ltd. ISBN Revised 5 th Dec