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Could highway trains be the future of mass public transport?

The transport industry faces a number of key challenges, notably congestion, safety and effects on climate. Increasing the use of public transport and reducing the use of cars is generally considered to be of overall benefit to the community, but this is often to the detriment to the individual in terms of convenience and direct cost.

Sometimes we must think further ahead and consider new transport concepts. One new idea for mass public transport is the ‘highway train’. Unlike platoons and road trains, this concept involves a new type of vehicle: a form of hybrid carriage with some of the characteristics of both a bus and a train.

In the highway train, battery powered carriages similar to buses would operate independently on our existing urban and rural road network, then link together with a diesel powered locomotive on motorways and major roads.

The key operational aspects of the concept are that the locomotive is a dedicated unit which continuously moves along specified motorways or major A-roads at an optimised speed for efficiency. The carriages dock automatically with the locomotive / carriage stack so they are linked to allow passengers to move along the highway train whilst it is in motion. Personalised information services would advise passengers when a carriage change is required for their intended destination, and the carriages would leave the train at different points along the highway to go to different destinations. This would give passengers a wide selection of destinations without having to use a hub (bus or rail station).

road train

A passenger version of the road train concept used for freight in Australia could form part of mass transit strategies

The key physical aspects of the concept are electrically powered carriages, using batteries whilst on their independent urban routes, but plugged into the locomotive on the longer sections of the route for direct power and battery charging. Whilst docked, the carriages retain drive, steering and braking within the train arrangement, which is controlled by the locomotive. The carriages can also separate temporarily within the train to allow a new carriage in or an existing one out in order to optimise scheduling.

By using electric power in urban environments, CO2 and noise emissions would be reduced compared to conventional buses. In order to maximise efficiency, each highway train would be powered by a large and highly efficient internal combustion engine which would charge the battery of each carriage whilst it is docked.

Passengers would board carriages at designated stops on a local level and each carriage would be capable of operating on all sizes of road, allowing passengers to be picked up in both densely populated and rural areas. Once passengers have boarded a carriage, the vehicle would then head towards the nearest highway to join up with the closest highway train. The highway train would then power and recharge the carriages until the time came for them to detach and exit the highway. 

Each locomotive would be piloted by their own driver and initially each carriage would be driven by its own driver, but all would become more autonomous as technology and public opinion develop and costs reduce. Whilst connected to the highway train, carriage drivers would be able to rest as the locomotive driver would take over control of the vehicle.

The key benefit of the highway train for the user is the point-to-point conveyance without having to wait for vehicle changes at potentially uninviting stations. The benefits to society are many fold. Reducing urban congestion due to a smaller number of cars on the roads, and inter-urban congestion due to a higher traveller density per road mile compared to a line of cars. A reduction in noise and local pollution in the urban environment due to electric drive, and the use of an efficient and optimised locomotive (due to its large size and narrow duty cycle) would minimise fuel consumption and emissions on the motorways. Finally, expensive new infrastructure would not be required.

Governments could also benefit from the concept, as the cost and time associated with developing a new vehicle is minimal compared to building new infrastructure, meaning that the solution could be implemented quickly. The versatility of the highway train concept also lends itself to the possibility of carriages being re-directed to different destinations depending upon passenger numbers and special events. This versatile approach to transport may in turn help to further reduce Government spend on travel services, as highway trains would not have to run regardless of passenger numbers as is the case for conventional trains.

To realise the concept, a number of new technologies will be required, and some of these are already in development.

By integrating the rollout with traffic management systems, highway trains would be able to avoid oncoming congestion by redirecting the vehicle along other routes. The improvement of traffic flow would in turn reduce journey delays and vehicle emissions, as the highway train would be able to maintain a constant speed and avoid stopping and starting. Carriages could also be equipped with their own braking and steering systems as well as torque vectoring technologies to enable the highway train to steer around obstacles and brake heavily without jackknifing. 

Clearly this concept is radical and some new technologies would need to be developed in order for this concept to work, but engineering some radical new form of transportation could prove to be the only cost effective and sustainable option for the future.

Readers' comments (11)

  • it wont work. could you imagine a "road train " trying to stop and start to collect passengers then start going again,holding up the rest of the traffic. as for trying to get something this long along rural roads....
    a local firm Denbys tried a similar idea for goods transport. it didnt work or wasnt allowed on the highways.

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  • I fear that the previous contributor may have missed the point.
    The locomotive would not stop. As I understand it, the locomotive is a 'mothership' to which several electric coaches can attach to at any time. The locomotive would stay on a main highway, for instance constantly circling a ring road, whilst the coaches would attach / detach randomly to follow local routes. Because each carriage is powered, the train could temporarily break anywhere at any time to allow a coach to leave / join.

    My one concern is the charging capacity for coaches attached for a short time, but that should not stop further investigation of what seems a well thought out approach

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  • Roy hodson has missed the essntial point I think. Carriages can drop in or out of the train while it is in motion, even from the middle of the train. They then operate autonomously. No need, therefore, to foul up the road network by stopping and loading/unloading a complete train.

    As a concept, this is elegant. Hope it gets proper attention.

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  • The problem will be to find a route that enables the 'road train' to keep moving. Just taking its passengers out of their cars will not free up enough road capacity now, let alone when it may find its way into operation.
    The main drawback with mass transport is the interconnection time. I find that the majority of my journeys are quicker, door to door, by car even taking into account the traffic delays.
    It would be interesting to see calculated journey times from town centre to town centre by 'road train' compared with those calculated for HS2!

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  • I was a Railway engineer for some time and heavily involved in electrification. It seems simpler to me to just have hybrid diesel/electric buses that link up as they meet rather than bothering with a separate locomotive. If the loco is to be able to charge the trailers it would need a serious prime mover and complex cables though the train. Linkable buses would need the drive, sensors and control systems to allow independent operation before/after linking so why not let the one that happens to be in the lead take command? - In train terms, use multiple units rather than locomotive. Hybrid buses would be more fault tolerant and wouldn't need the controls reconfiguring, this takes noticeable time for the lead vehicle to work out what's going on. A train of hybrids still has the advantage of lower wind resistance and collision avoidance.

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  • Very interesting concept and (apart from one) some good comments too. Imagining a journey from, say, rural Kent to the centre of Birmingham might be stretching a bit far, but having this type of facility around the M25 could save the queues and frustration for many 'commuter' drivers.
    Worth further investigation

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  • Why is this proposed for the roads ?
    A much more ensible approach would be to implement it on the railways. It would mean some modification to the railway infrastructure but would be an incredible system when completed.
    We could then sell it to the rest of the world.

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  • Autonomous engines + very smart computers linking vehicles communications and physical linkage optically and magnetically to each other with ability to decelerate, decouple and accelerate and engage, even if you are in the middle of a 'train' of engaged vehicles. The computers will negotiate a sequence, alerting the entire 'train' that an 'event' (pickup, discharge, emergency stop, destination release, change of plan..etc) is occurring and launch the sequence for all units in the train to complete the 'event' safely. If the unit operator fails to respond, is asleep or ill, the train is safely slowed and the non responsive vehicle is 'parked' safely on the side of the road and will await dispatched assistance. Wow.....why not just turn the roadways over to Walt Disney Imagineering Department!?!

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  • Interesting concept. To clarify, each 'Battery' powered coach would have it's own Internal Combustion Engine powered generator to charge the battery whilst coupled in a train. Why not just use the engine when decoupled? The train loco should be capable of hauling and controlling a set maximum of coaches so for coaches to have another loss making, weight penalising generator and associated electrical accumulators seems senseless.
    On another level, these trains would mean passengers who want to go to a different destination than their original coach would need to move to another coach or even more complex move to a coach that will change trains so they can then possibly move to another coach ad nauseum until they find a coach going to their final destination. I foresee many disgruntled passengers as they try and retrace steps lost.
    So, as I said, an interesting concept.

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  • Many thanks to all for your comments.

    I would like to clarify some of the points as best I can.

    To Robert Baker – yes, charging time could be an issue, particularly if a “last on – first off” carriage process was adopted. The idea of splitting the train could allow only “well charged” carriages to leave and if we assume that the route away from the highway is known, the likely energy level required for that carriage should be reasonably predictable. It’s true, it requires some thought and planning , but there is no fundamental technological barrier to implementing this type management system.

    To Dragonslayer – I agree with all your points and agree this will never be a direct replacement for a car. However, it may be more palatable than a bus or train solution and if it can be cost competitive, may ease some car drivers out of their cars for some (or more) journeys. I too would like to see a comparison with times compared with HS2! I suspect the infrastructure cost of the highway train concept should be quite a bit less though.
    To Tony Foster and John – It would be great to implement the basic concept on the railways – either with or instead of on the roads. I think there is one huge problem however – it would most likely require the entire rail system (or a very large chunk of it) to swap from the current mode of operation, almost overnight! That will never happen. The disruption would be immense and the risk would be huge. Can you imagine Network Rail agreeing such a change-over? By doing it on the roads, it can be introduced gradually as an “overlay” system additional to the existing transport systems, with the unforeseen problems being ironed out as they are encountered on “living lab” or real world trials. I think it has a far better chance of seeing the light of day on the roads even if it could be better implemented on the railway network.

    To answer some of Tony Foster’s specific points, diesel electric hybrid road vehicles make little sense unless there is a need for a zero emission mode (in city centres, for example). Heavy haulage truck companies are extremely sensitive to fuel consumption – if diesel hybrids made any economic sense, all heavy trucks would have them now. Diesel electric trains are series hybrids with a transmission adopted for ease of applying power to the tracks, not for outright efficiency.

    The “multiple unit” approach certainly does have some merits and I would certainly like to be able to compare this and the locomotive strategies in more detail. As a general rule, large prime movers are more efficient than smaller ones, and the highway train locomotive would certainly need to be relatively large. Would the improved economics of scale of diesel multiple units offset the reduction in efficiency relative to fewer, larger locos? I don’t know – but it would be interesting to find out.

    To Gary – all those technologies exist and could (in theory) be applied pretty soon. Do we want them enough to pay for them though? Also, a lot of wacky technologies from the film studios have become reality. The Star Trek communicator was widely ridiculed as impossible when I was a kid – but my smart phone does all that and even video comms today, admittedly, it is not yet intergalactic!! I don’t necessarily want Disney running our roads, but I do keep an eye on what they imagine might exist in the future – engineers have a habit of turning versions of such ideas into reality. That’s what makes life as an engineer so interesting!

    Thanks for your comments – please keep them coming!

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