Electric road systems
One means of decarbonising road freight transport is electrification of goods vehicles, provided the carbon intensity of electricity generation drops in line with the energy sector’s renewable energy targets. However, given the weight of heavy-duty vehicles (HDVs), their electrification is challenging. With today’s technology, battery systems delivering the required power and driving range would be so large and heavy as to significantly reduce vehicles’ payload and render their operation inefficient.
Electric road systems (ERS) can provide a solution for HDV electrification. In ERS, the road infrastructure supplies vehicles with electricity. As a result, vehicles need not rely on on-board battery systems for the part of a trip that is carried out on ERS-equipped road infrastructure. This makes efficient, long-haul heavy-goods transport based on electricity more feasible.
ERS solutions differ according to how energy is transmitted to a moving vehicle. The following three alternatives are being pursued in test applications:
- Conductive overhead catenary systems transmit energy via a pantograph mounted on a vehicle’s roof, similar to the type commonly used for trains, trams and trolleybuses. The system can be integrated with and operated on the existing road infrastructure.
- Conductive rail systems transmit energy to rails in the ground and thence to the vehicle via a slide-in current collector system – a movable arm that detects the rail. When overtaking, the arm can automatically raise; when stopping, the current is disconnected.
- Inductive charging systems transmit energy from the road to the moving vehicle wirelessly via a magnetic field. They require installation of coils in the road that generate an electromagnetic field, as well as receiving coils on the vehicle for electricity generation. There is no mechanical contact between the two.
To get to and from an electrified road stretch, HDVs using electrified roads can be either fully electric or hybridised. Batteries can be recharged on an ERS stretch, allowing electric driving when away from ERS-equipped road infrastructure.
So far, ERS have mainly existed on test sites, although in recent years initial tests of conductive ERS have been carried out on public roads. Inductive ERS for HDVs have not yet been tested on public roads. In Sweden, two systems were demonstrated on public roads, each with a length of 2 km.
ERS offer a more energy-efficient solution for trucks than diesel and other alternatives, including hydrogen or natural gas. Given the high cost and long-term nature of the investment, electric roads are most suitable for trunk highways with high demand volume. Operations using electric roads would have shuttle-like elements, with heavy trucks on electric roads travelling between major centres of demand generation/consumption (e.g. distribution centres, ports, terminals). ERS would necessitate significant investment in infrastructure.
Vehicles charged via ERS do not cause tailpipe emissions on an ERS-equipped road stretch. The emission reduction potential depends on the degree of electrification of the HDV, its overall energy efficiency and its use on non-ERS road stretches. Regarding pollutant emissions and noise, potential reductions will vary with the proximity of the road stretch to urban areas or residential zones. In the case of CO2 emissions, actual economy-wide reductions depend on the carbon intensity of the electricity used to power the vehicle. Studies have shown that ERS has greater CO2 reduction potential than any other mitigation option for road freight transport.
Like other solutions for electrifying the transport system, ERS increases electricity demand in transport. In terms of the transport system’s overall carbon impact, ERS will only be beneficial if the roll-out of such systems is accompanied by decarbonisation of the electricity system. In terms of the impact of ERS on the electricity grid, it is expected to be less demanding than more conventional battery vehicles. This is because continuous electricity supply via the ERS allows for smoother load profiles on the electricity network.
ERS can also have an on impact mode shares. Where ERS allows for significant cost reductions in road freight transport, it could become more cost-effective than rail transport.
Investment of public funds will be required for the initial development of the network, as a minimum level of coverage would be needed before operators would consider electrifying their fleets. International co-operation on cross-border routes would be required to ensure interoperability.
The environmental benefits and potential financial advantages for vehicle operators have to be balanced against the cost of ERS. Cost items relate to i) infrastructure (e.g. electrical wiring and rails or poles, connections to the electric grid, substations with transformers, control units, related civil works), ii) vehicles (cost of hybridising or fully electrifying the drivetrain, often expressed in comparison to a conventional HDV) and iii) infrastructure maintenance.
Estimates for the three types of system (per kilometre, two lanes, on existing road infrastructure) are:
- Overhead catenary: EUR 1.5–2.5 million
- Conductive rail: EUR 0.7–2 million
- Inductive charging: EUR 3.1 million +
Utility companies might have a role in funding the infrastructure. The business model of ERS is yet to be determined.
ERS will accelerate uptake of hybrid and fully battery-electric vehicles in general, in the freight sector and elsewhere, as it will help drive down the cost of related technology.
ERS infrastructure is expensive to set up and maintain. Although there are as yet no clear-cut solutions for zero-emission HDVs, developments in battery technology, hydrogen and other fuels (bio or synthetic) cannot be ruled out as a dominant solution for the decarbonisation of HDV operations. Such alternatives might end up providing zero- or low-emission HDVs at lower cost to government.
ITF (2021) Transport Climate Action Directory – Electric road systems
https://www.itf-oecd.org/policy/electric-road-systems
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