David Crawford describes a Brazilian advance in clean urban public transport.

Advanced Hybrid Electric Buses (HEBs) are currently achieving up to 50 per cent fuel savings on a segregated corridor in Brazil’s largest city of São Paulo, as compared to HEBs or buses with conventional diesel-fuelled Internal Combustion Engines (ICEs) on general traffic routes.

Running since 2007 on a former ‘white-elephant’ busway, a fleet of 15 new 15m (45ft)-long HEB vehicles is moving up to 25,000 passengers per hour across the city in the first stage of a planned network of new Bus Rapid Transit (BRT) links.

Their presence is the result of a modelling exercise carried out in the UK using experience gained in an EU-funded project. The initial São Paulo implementation is on the largely elevated 8.05km (4.9 mile)-long D Pedro II-Sacomã corridor that crosses a very busy area of the city.

It links the central business district to southern suburbs, with metro connections at both ends, and forms the first stage of the city’s planned north-south Tiradentes Express BRT service. The elevated section was built to raise the southern stretch above areas which lie alongside the River Tiete and are subject to flooding.

Legislative imperatives
Its importance is highlighted by the fact that the city’s existing commuter rail and metro links largely run east-west through the centre. Because of increasingly strict Brazilian anti-pollution regulations for new transport projects, vehicles using the corridor had to be low-emission and the initial plan was to use zero-emission trolleybuses.

But the cost of electrification on top of the construction of the elevated route proved too high for the city’s public transport administration São Paulo Transporte (SPTrans). It therefore had to look for alternative vehicle types to bring the corridor into use.

At this point, Brazilian transport consultant Dr José M Marquez – now with Scott Wilson’s Bristol (UK) office – suggested HEBs as a solution which, though not emission-free, could still meet required environmental targets. At the time, he was at the University of the West of England (UWE) in Bristol.

He had been invited by the Faculty of Computing Engineering and Mathematical Sciences to work on the EU-supported Ultra Low Emission Vehicle – Transport using Advanced Propulsion 1 (ULEV-TAP 1) project and carry out PhD research on Hybrid Electric Vehicles (HEVs).

The project was developing the technological components for a hybrid light rail vehicle that could run independently of any external power supply, using a flywheel as the Energy Storage Unit (ESU). But Marquez’s HEV model, using German company PTV’s VISSIM transport and traffic strategy simulation system, proved capable of being adapted to buses – as in simulating road characteristics for possible BRT routes in central Bristol (a continuing project).

Evidence base
SPTrans wanted evidence to support the case for the large-scale introduction of HEBs Рas did the Brazilian National Bank for Economic and Social Development (BNDES), which was funding the relevant second phase of the Ṣo Paulo Integrated Public Transport Plan (IPTP). This imposes strict environmental criteria in line with Brazilian government policy.

The requirement was for an independent study to demonstrate that HEBs plying the corridor would produce satisfactorily low emissions and deliver fuel consumption savings. Brazilian consultants Herjacktech, who advise SPTrans, then contracted Marquez to carry out the modeling.

He inputted the route characteristics of the D Pedro II-Sacoṃ corridor, using the 16.1km (10 mile) drive cycle of an outward and return journey. The route is largely free of gradients Рwith none of those that are present more than 200m long Рand so favourable for the deployment of HEBs, the use of which is restricted on long and accentuated ascents.

(For comparison, he also evaluated the characteristics of a second, 13.85 km /27.7km (8.6/17.17-mile) drive cycle corridor, running between São João and Pirituba. Again, this has few gradients but is not segregated and so experiences conflict with general traffic, relying on bus lanes to keep operational speeds at around 30 km/h (18.6mph).

‘Vehicle’ characteristics
For vehicle characteristics, the model used the characteristics of an HEB powertrain system manufactured by locally based Eletra Industrial Ltda. The company had already developed the HEB concept beyond the experimental stage, using advanced diesel engine technologies.

It had been carrying fare-paying passengers using prototypes since 1999 in the municipality of São Bernardo do Campo, part of the Greater São Paulo Region. Simulations covered 12m, 15m and 18m (36/45/54-foot) bus lengths.

Comparison of fuel consumption and emissions showed improvements achieved by the reduced size of the HEB’s diesel engine and its operation, on segregated track, at minimum specific fuel consumption levels. The savings on emissions are a function of operating the HEB’s smaller engine at near maximum efficiency for long periods of time.

The HEV model has also proved a useful tool for testing different HEB characteristics to enable optimisation of key components and provide a balance between performance, fuel consumption and emissions. Although the costs of investment in HEBs can be higher than those of conventional diesel buses, Eletra was able to show evidence that HEB running costs are about 30 per cent lower in comparison.

The simulation results, tested by Brazil’s Federal University of Rio de Janeir (UFRJ), convinced SPTrans and the BNDES of the advantages of investing in HEB technology for public transport, as being both less environmentally damaging than conventional diesel buses and capable of considerable reductions in emissions.

Comments Marquez: “Very little globally has been done to date to increase public transport participation in solutions aimed at reducing exhaust emissions within the world’s cities and meeting environmental limits fixed by the Kyoto protocol.

“Local transport authorities have not addressed, so far, ways of implementing suitable public transport as a means of improving people’s health. São Paulo is an encouraging example of what can be done.”

The model
The HEV model is designed to simulate vehicle performance and enable analysis and comparison of fuel consumption and emissions as between HEVs and other vehicles. Specially created for public transport, it runs on real city centre drive cycle and vehicle configurations and allows calculation of energy and power demands, vehicle performance, driving range, fuel consumption and emissions.

It can use speed, acceleration and deceleration data from real routes, modelled in VISSIM for control strategy development, ESU optimisation, traction motor and engine selection, and fuel consumption and emissions predictions.

It enables simulation of the stochastic features of traffic flow in real time, following identification of traffic bottlenecks or busy transport corridors where pollution levels are a cause for concern.

The model operates within The MathWorks Matlab numerical computing environment and programming language, using associated Simulink tools to simulate and model the vehicle and its components and allow accurate analyses of results. It remains available for similar exercises.

HEVs are designed to have the same range as conventional petrol or diesel vehicles, and to deliver the same level of performance, but with less damaging impacts on the environment. In public transport, they have lower investment and running costs compared with electric-only Vehicles (EVs) – which, while they produce zero local atmospheric pollution, need an overhead or in-road infrastructure to access a power supply. This makes HEVs more flexible in routeing terms.

They also overcome the problem of the limits of the battery-powered EV on mileage range and performance,

HEVs are built with a Prime Motor Unit (PMU), which can be a fuel cell or an ICE, coupled to an electric generator. The ICE is smaller than in conventional vehicles, contributing to the required fuel consumption savings and emission reductions.

The PMU combines with an ESU. This can be a battery pack, flywheel or ultracapacitors providing energy to the electric traction motors on the vehicle’s axle.

DATED: 6th October 2008