Energy Transition Challenge for Bus and Coach Public Networks
18 October 2019

Energy Transition Challenge for Bus and Coach Public Networks

Energy transition for public transport networks: this expression, heard so often, seems familiar to us. However, we are only at the beginning of the story that will shape future transport network operations. Marc Boudier, Project Manager in SYSTRA’s Consulting Division, gives us the key factors to define energy transition strategy for our public road transport networks. What are the possible technology choices? What is changing towards oil era? Is there a duplicable recipe for every territory? How can those ‘clean’ technologies be mastered? What are the associated costs and risks?

The Paris Agreement was signed in 2016 by nearly 200 countries in the world: its goal is to limit global warming to 1.5 degrees Celsius by mitigating greenhouse gas (GHG) emissions and making finance flows consistent with that goal.

Even if the measures are not mandatory, signatory countries to the Paris Agreement have to respect certain principles: strategy 20/20/20 (reduce carbon dioxide emissions by 20%, increase renewable energy production by 20% and increase energy efficiency by 20%), nationally determined contributions (NDC) on GHG emissions that represent a progression over time.

Being the second most important sector for GHG emissions, transport has indeed a key role to play in the successful implementation of the Paris Agreement.


Cleaner public road transport will trigger a better local environmental quality (air quality, sound environment…) that will have to be confirmed regarding the global environmental footprint of the technology. Nevertheless, implementing a transport network with limited efficiency or an inappropriate response to local mobility needs, would not make more sense with cleaner energy than with oil. Thus, the energy transition process needs to examine the efficiency of transport networks and implement the following actions:

This is a quality approach to defining a transport network: robust (reliable, variation resilient), flexible (needs adjustment, interoperability, multioperability), and accessible (clear information, easy access, attractive price, adjustment to type of population such as persons with reduced mobility).

After leading these actions to consolidate the existing transport network, we can engage in the next steps. Which technologies are available? What is changing compared to Diesel?


Studying the energy transition of public road transport, the first technology that comes to mind is electricity. There are 3 kinds of electricity technologies that use batteries:

  • Slow charging (the vehicle is charged for hours out of operations, often during the night at the depot);
  • Fast charging (the vehicle is charged for a few minutes, several times along the operation day often at a terminal or sometimes at some intermediate stations);
  • Trolleybus (bus charged on operations under electric line; new generations include small batteries allowing autonomy out of the electric line).

Well spread in a few districts in China (we can quote the main one in Shenzhen), the electric technology on battery is starting to be deployed on a larger scale in Europe progressively with the renewal of bus fleets.

However, the ‘all-electric’ approach has some limits, not only regarding vehicle autonomy but also the environmental balance based on low-carbon electricity and battery production with rare metals. That is why, considerations are turning towards a transition including energy mix.

Throughout the world, another technology is commonly integrated as cleaner than Diesel buses: the CNG vehicles (compressed natural gas). This technology is mature and is coming back under the spotlight providing autonomy and cost advantages. As natural gas is also a fossil source of energy that emits CO2, all the stakes lie in supplying with bioCNG (renewable CNG produced mainly via a process of waste mechanization).

Another technology, still in a confidential state of deployment, lies in dihydrogen produced by the electrolysis of water process. This process with low-carbon electricity has a good environmental balance but is energy intensive: 2 or 3 Kwh electricity are needed to get the energy equivalent of 1 dihydrogen Kwh, which makes the technology expensive for bus use.

Finally, other solutions based on more ‘exotic’ energy sources can be interesting for some territories. Among them, we can quote the use of some biofuels.


A Diesel bus network uses a proven and mastered technology that no longer fits with the standards regarding GHG emissions. Tomorrow, with clean energy technologies, we can no longer think ‘material means for a bus network = vehicle procurement’. The vision must change and address the issue as a system. Firstly, a transport offer is defined then operation services are built to answer it and finally the system should be sized to meet operations requirements. Clean technologies require an organization change and training for skilled employees.

To make energy transition sustainable, the following criteria are to be closely analyzed, that will help decision-making among the available technologies:

  • Vehicle autonomy
  • Charging/fuelling time
  • Securing energy supply
  • Flexibility for transport offer evolution (for instance commercial route lines)
  • Global investment costs
  • Global operation costs
  • Local environmental balance on the technology lifecycle
  • Global environmental balance on the technology lifecycle
    General assessments of main ‘clean technologies’ according to these 8 criteria are presented in the table below.

As we can notice, the technology matching perfectly with all criteria does not exist. The first prism to choose the adequate technology is operation needs. To assess the performance of ‘clean technology’ answers to those needs, bus (or coach) services are generally spread according to daily kilometres and required autonomy. A second prism is the territorial context: indeed, existing energy facilities and territory projects are key factors to be taken into account.

If one technology is adopted to answer all needs, we keep a mono-energy system. In other cases, we are talking about energy mix.


A careful analysis of territory assets will be very helpful for decision-making on energy transition strategy. All energy supplying networks like electricity or gas come naturally to our mind and in developed countries generally benefit from a good territorial coverage in the urban environment.
However, a territory can also use synergies linked to specific activities that produce waste valuable for energy transition. In wine-growing regions for instance, grape marc can be used to create ethanol biofuel.

Some other territories can benefit from industrial activities producing dihydrogen as waste material: in Germany and the Netherlands, this solution is used to fuel buses with dihydrogen at a very affordable price.

Another way to benefit from territorial synergies is to pool energy stations. Compared to electric stations that are more difficult to mutualize between heavy and light weight vehicles for power and charging time reasons, CNG stations are much easier to pool. Indeed, we quickly understand that bus and coach networks’ energy transition can be considered as a first step to a wider strategy for mobility as a whole. Public CNG stations will be an asset not only for public transport networks but also for freight and individuals.

Today, our mobility is deeply dependent on the daily oil price where production is concentrated in a few regions of the world. This is an important risk for mobility and economic balance that needs to be considered, whereas energy transition compliant with a high-level energy strategy can strengthen energy supply independence with several years of supply contracts including agreements on volumes and prices. However, as every main developing sector, energy transition needs to know and control specific risks.


Risks that need to be hedged are directly linked to the chosen technologies. It would be illusory to quote all of them. The table below lists major risks and means to prevent them. In any case, the aim is to ensure sustainable continuity of service of bus and coach networks from the beginning of energy transition.

Beyond risk management, every community engaging in public transport energy transition will face the need to contain costs.


Knowing the constraints on public finance and recent strikes in the world due to higher taxes, controlling the energy transition costs is vital and a key success factor. So far, main operation costs on Diesel vehicles are split into 3 categories (out of driver income): rolling stock (bus or coach), maintenance and fuel. Tomorrow, with clean technologies, infrastructure costs and some components renewal costs like battery, fuel cell will have to be considered.

The graph below compares (based on European prices) annual costs per technology compared to Diesel: dihydrogen, electricity slow charging, CNG (compressed natural gas) and bioCNG.

A 50-bus network (half-standard buses and half-articulated buses) has been modelled: parked in one depot and operated at 60,000 yearly kilometres. Charging/fuelling infrastructure is included in the model contrary to civil work costs.

Comparing clean technologies, CNG seems to be the best solution from a financial point of view. This is why several communities in the world have already chosen the technology for their bus network. Nevertheless, CNG is still a fossil energy that emits GHG, only 25% less C02 compared to Diesel.
The solution based on bioCNG (CNG from renewable sources produced by the waste mechanization process) is more environmentally friendly but its cost is 3 or 4 times that of fossil CNG. Moreover, supplying bioCNG can be limited because waste from 7,000 people is needed to feed only one bioCNG bus.

The dihydrogen technology still keeps higher costs, 2 or 3 times higher compared to Diesel technology, even if maintenance costs should decrease going from pilot tests to more industrialized developments. Our model has considered price reductions on rolling stock thanks to European mass procurement projects like JIVE (Joint initiative for hydrogen vehicles across Europe).

Electric technology has some financial advantages in countries where this energy source is affordable, and supply does not suffer from shortages. With wider deployment, battery costs should decrease if free market rules are still followed. However, there is a risk of increased dependence on a few countries that master battery technology and access to rare metals.

Depending on the national and local energy sector context, some solutions will be more adapted to one country rather than another regarding environment and cost aspects. Nevertheless, in most countries throughout the world oil is taxed, generating substantial revenues for governments. As a result, every move from Diesel to clean energy mobility will need consideration on energy-mobility taxation. Any change in energy taxation would change the economic equation.

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