Energy transition challenge for bus and coach public networks

La transition énergétique dans les réseaux de transport : cette expression tant usitée nous paraît familière, alors que nous ne sommes qu’au début de cette mutation et que celle-ci va bouleverser l’exploitation des réseaux de transport que nous connaissons.
Marc Boudier, Responsable d’études à la Direction Conseil et Aménagement de SYSTRA, donne ici les clés pour définir une stratégie de transition énergétique pour un réseau de transport en commun routier. Quels sont les choix technologiques possibles ? Qu’est-ce qui change par rapport à l’ère du tout pétrole ? Existe-t-il une recette duplicable sur chaque territoire ? Comment maîtriser les nouvelles technologies dites « propres » ? Quels sont les coûts et les risques associés ?

En France, la loi de transition énergétique pour la croissance verte (LTECV) a rendu obligatoire la mutation des réseaux de transport collectif routier vers des flottes de véhicules propres pour les agglomérations de plus de 250 000 habitants, ainsi que pour les communes de toutes tailles soumises à un plan de protection de l’atmosphère. Les agglomérations concernées devront réaliser cette transition énergétique partiellement à partir de 2020, et complètement à partir de 2025, au fil des renouvellements de flottes de véhicules.

Cette législation a un double effet : d’une part, elle renforce les nouvelles filières de mobilité sur les territoires concernés, d’autre part, elle pousse les villes non directement soumises à la LTECV, pour ne pas perdre en attractivité, à se poser sérieusement la question d’aborder la transition énergétique – au moins partiellement – sur leurs réseaux. Ainsi, les réseaux de bus et de cars des grandes agglomérations deviennent les chefs de file de la transition énergétique pour les autres réseaux de transport urbain, ainsi que les chefs de file d’une mobilité propre à un sens plus large, étendu aux territoires interurbains, aux véhicules légers et aux nouveaux modes de mobilité (vélos, trottinettes…).


The European Union has fixed a legal framework per country with some objectives for renewable energy market share. Also, new cars manufactured in Europe will have to emit carbon dioxide below yearly thresholds aimed at reducing emissions to under 95g per kilometre in 2021 then reducing this figure by 37.5% in 2030.

Some European countries like France have enacted ambitious laws for energy transition in public transport: by 2025, in French agglomerations with more than 250,000 inhabitants every bus should be renewed with clean technology: this means mainly buses running on electricity or gas. Some other European countries have also enacted a 2025-2030 milestone for clean renewal of public transport buses.

In the US, even if recent political signs have not been necessarily in favour of green awareness, and even if clear climate change legislation is not enacted yet, the number one GHG emitter in the world still has officially a plan to reduce GHG emissions by 26-28% in 2025 (compared to 2005) using an existing law (The Clean Air Act) and certain measures: Clean Power Plan, Energy Efficiency Standards, Methane Action Plan. Moreover, at a subnational level some states have enacted a legal framework on climate change like the leading state California: Global Warming Solutions Act, Environmental quality Act with GHG emissions provisions.

These legal frameworks in favour of climate change have a double positive impact: on the one hand, they strengthen the new mobility industries with cleaner solutions, on the other they seriously push cities and territories that are not directly involved to tackle the energy transition issue if they do not want to lose attractiveness vis-à-vis their neighbours. Indeed, big agglomerations that engage the energy transition process for their public transport fleet will become leaders of a cleaner mobility not only for bus fleets but also for coaches, cars and new mobility modes like bicycles, electric scooter trolleys…


Cleaner public road transport will trigger a better local environment 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);
  • and the 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 methanisation).

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 organisation change and training for skilled employees.

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

Vehicle autonomy

  • Charging/fueling 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 mutualise 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/fueling 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 methanisation 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 industrialised 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.

Don't miss anything, follow us on social media !
quis mattis risus eget felis accumsan Sed