James Joyce, in Ulysses, tracks the various wanderings of his characters, both major and minor, across Dublin’s electric tram network of the time. Father Conmee worries about the solemnity of the fellow occupants in his tram, Blazes Boylan seeks to deliver a gift via tram, and Bloom muses how property prices would rise if there were a tramline on the North Circular Road.
Horse-drawn trams had been introduced to Dublin in 1872. Overhead lines first appeared in 1896, when the Dublin Southern Districts Tramways ran their pioneer electric trams between Ballsbridge and Dalkey. By early 1901 most of the almost 100km of lines in and around Dublin had been electrified, and the last horse-drawn tram ran from the city to Sandymount.
The first ever catenary tram had been demonstrated at the 1881 International Exposition of Electricity in Paris. The inventor was Ernst Werner Siemens, who had co-founded in 1847 what became the Siemens company. The first operational tram service with overhead lines was launched in 1883 in Austria.
Today we are familiar with the catenary Dart and Luas systems. Some cities, such as Athens, Geneva and Sarajevo, have electric trolleybuses powered by overhead lines. Clearly, overhead lines are a well proven technology, with decades of operational experience worldwide. After the initial capital outlay, catenary systems also have relatively low maintenance and repair costs.
As we transition to rapidly move away from fossil fuels to electric transport, could a renewed investment in overhead lines make a substantial contribution?
About a quarter of global carbon emissions come from transport. Within this sector, rail (both passenger and freight combined) accounts for just 1 per cent. Shipping accounts for 11 per cent, and aviation for 12 per cent. Passenger road transport accounts for an astonishing 45 per cent, and road haulage for 29 per cent.
The momentum to electric cars and buses for passenger transport is clearly building, but what about road freight haulage? Electric trucks require higher capacity, and hence heavier batteries than e-cars. Furthermore, the relatively limited range of long distance electric lorries is currently a concern for the haulage sector. Even assuming there were a widely available charging infrastructure, the recharging time for electric trucks would be a worry for freight operators.
In 2016, Siemens inaugurated an overhead line above a two kilometre stretch of motorway just north of Stockholm. In partnership with Scania, a manufacturer of heavy freight lorries, two prototype trucks were demonstrated using a hybrid-diesel engine combination, with the electric motors powered directly by the overhead lines. Since then, there have been trials at Los Angeles and at three sites in Germany, with the longest motorway stretch so far of eight kilometres.
The key innovation has been the design of a pantograph – the adjustable frame connecting the overhead cables to the vehicle – that can smoothly engage and dis-engage from the overhead lines while the vehicle is moving at motorway speeds. The system can be set to automatically sense an overhead line, deploy or retract the pantograph, and fluently transition to and from electric working.
Rather than a hybrid engine, fully electric operation becomes feasible if batteries are automatically re-charged by the overhead lines during motorway driving. If motorway overhead lines were widely available for long distance haulage, then smaller capacity and lighter batteries could be used just for local driving when off-motorway at the start and end of a journey.
With the advances in autonomous-driving technologies, including lane detection, speed management and collision avoidance, it is possible that long distance lorries could drive themselves keeping to a motorway lane with overhead lines. This in turn would allow haulage drivers to relax and rest, and normally only have to take control when driving off-motorway.
In a 2018 report, the German Federation of Industries (BDI) recommended building overhead lines for up to 8,000km of the 13,000km autobahn network, as the cheapest way to reduce carbon emissions from its road haulage sector. Sweden has also commissioned a study for the electrification of 2,000km of its roads, and is aiming to make its entire transport sector carbon-free by 2030.
There is of course a “chicken and egg” challenge: haulage companies will not invest in suitably equipped electric trucks, until there is an overhead line infrastructure, but without such trucks there is no incentive to build out the overhead line network. The current design of overhead lines and associated pantographs are only applicable to freight lorries, and are not appropriate for e-cars.
The European Commission has noted that there currently is no international agreement to enable overhead lines to smoothly operate on motorways across borders. Competitors of the catenary truck system observe that it may be better to continue the investment in heavy capacity battery systems for electric trucks, and roll out EU-wide re-charging stations for the haulage industry.
Turning a corner on North Circular Road, Joyce’s Father Conmee wondered why there was not a tramline in such an important thoroughfare. Perhaps there will never be electric lines above the major motorways of Europe.
