Intermodal Freight Operations
by Matthias Beth
1) Intermodal transport
Intermodal transport deals with carrying freight using specially
designed carrying and cargo protecting units that can easily be
swapped between several transport modes, e.g. road, rail, inland
waterways, open seas, air.
This avoids unloading and reloading of individual items but results in a lower overall payload due to the duplicated load-bearing elements of the rail vehicle and the load carrying units.
As a transport system, intermodal business tries to combine specific advantages of otherwise competing transport modes to achieve an overall gain for all partners involved.
In some countries, road vehicles used mainly for intermodal transport get a tax redemption and these may carry a heavier load, thus commercially compensating for the higher dead weight of the units carried.
Intermodal terminals are the transfer points and must take into account the very different properties of the transport modes involved, e.g., road with single load-units carrying stochastic traffic flows, as compared to transport by trains based on timetabled transport of consolidated loads.
In the intermodal business, many terms are used synonymously that have different meanings.
- Multimodal is any transport that uses more than one transport mode
- Intermodal are transports with load units swapped between transport modes
- Combined transport has most of the route travelled by rail or by ship to reduce road usage, minimum distance covered by rail/ship 100 km, maximum distance covered on road 150 km at either end, as defined in the EEC paper 92/106.
The following description of intermodal business aspects is based on standardised, widely accepted rail-road technology, available throughout Europe. This segment is in the focus of European transport legislation, i.e. activities of the member countries are co-ordinated and special funding is available for research and operation expenses.
3) Load units
There is a great variety of unit types available, allowing a wide choice of cargo to be carried.
(3 a) Standard lorries may be carried on "Rolling Highway" type low level wagons. The permissible undercarriage loading gauge is defined by ramp angles and wagon floor lids. Standard road vehicles may be carried by Channel Tunnel road vehicle carrying wagons without any size restriction.
(3 b) Containers are carried on flat wagons, ISO deep sea containers unrestricted, other container types if coded to combined traffic rules. Street transport happens generally on artics.
Container types may have different properties, e.g., chemical bulk at 34 tons in 20 feet of length, differing internal and external width, height and length, as container types include flat rack, open top and fold away containers. All containers may be stacked several high, deep sea containers up to nine, other types three, with the handling usually done via corner fittings.
Deep Sea Containers may be stacked several high and, when loaded, generally leave the terminal area shortly after arrival. Empty containers are sometimes left for longer term storage.
(3 c) Swap bodies are widely used in Continental Europe where they travel on truck-trailer combinations and are carried on railways generally on flat wagons and can be parked standing on retractable legs; they are basically similar to general road swap bodies wit grab pockets added to allow bottom lift.
This handling technology introduced by Freightliner in 1966 allows lightly constructed units without rigid top frame, thus they are not to be stacked. The bottom lift pockets allow several length versions and different makes of swap bodies, e.g., open top with tarpaulin cover.
Legged swap bodied can be parked standing on their feet, avoiding a second lift but needing time for lowering and raising the legs and making theft easier.
(3 d) Standard height semi-trailers may be carried in pocket wagons or EuroSpine wagon units, dubbed piggyback. They are derived from road semi-trailers with added grab pockets and with a stronger frame and need additional ground personnel helping with the support props and guiding the king pin into the recess. The elements beneath the load carrying surface are prone to accident damage and theft.
(3 e) The large number of intermodal units currently available does not allow fast changes to present technical details such as twist lock dimensions (top lift), grab pocket dimensions (bottom lift), bottom lock dimensions (road vehicle and rail vehicle connection via pins).
There are also differences in load unit usage between countries, e.g., swap bodies are widely used in Germany but in the UK flat semi-trailers are dominant in the road business.
4) Carrier wagons
The load mix greatly influences rolling stock choices, e.g., chemicals carried in tanks need more rigid wagon frames than swap bodies. Semi-trailers need their own special wagon equipment as well.
All wagons should be able to run at 100 kph, empty and loaded, as lower train speeds could incur higher track access charges. Central European railways’ procurement currently provides all wagons with empty and loaded speeds of 120 kph. Some specialised vehicles are available for 140 kph / 160 kph. Generally the higher air resistance reduces commercial viability, and singular high speed freight trains can not easily be run alongside general freight trains, during nights.
Trains would be allowed to reach lengths of up to 700 m, train masses up to 1600 tons.
(4 a) Container carrier wagons are the mainly used vehicles, designed to carry standard containers and swap bodies with lengths varying between 20 ft and 45 ft, with weights generally ranging from 2.5 tons to 38 tons
Carrying capacities of the different types
- two-axle wagon 40 ft 28.5 tons;
- four-axle wagon 60 ft 70 tons (some 73 ft),
- six-axle wagon 100 ft, 100 tons,
- eight-axle 110 ft, 100 tons
(4 b) Pocket wagons are the specialised vehicles to carry semi-trailers weighing between 7 tons and 38 tons. The road vehicle's weight is supported by its own wheels set down inside the pocket and by the king pin contact plate. The height of contact plate can vary between 980 und 1150 mm, so that a growing number of wagons can be adjusted in height accordingly.
(4 c) Low level wagons
Available route clearance or load unit height would either allow standard UIC wagons to be used, or might result in the use of special low level wagons (some 30 cm can be gained with low level platform frames and small wheels and some 60 cm can be gained with loading wells between bogies). 1155 mm level of load bearing surfaces is standard, with special vehicles having down to 820 mm on platform wagons.
5) Lifting equipment
Not the last or least of the questions to be answered is the type and number of lifting equipment. The main choice is between reachstackers and gantry cranes.
(5 a) Reachstackers can lift and carry all types of intermodal units and are quite flexible in their movements within the individual terminal as well as between terminals. They need an operational area of roughly 15 m width to move around between trains, lorries and storage positions. Wherever they need to move, it must be considered that the front axle carries up to 100 tonnes of static load on wheel surfaces of about one square metre.
Time needed to handle a single unit is quite short (1 to 1.5 minutes), but in the track area the reachstacker practically cannot serve more than one track and not more than two storage lanes, even though in dedicated storage areas third or fourth row stacking is achievable.
Reachstackers can easily cope with curved tracks. In the reachstacker’s favour, is that the terminal driver can be tasked to exchange paperwork with the customer driver, e.g., during off-peak service times, thus helping small-scale operations to become less marginal.
(5 b) Rail running gantry cranes need less surface - basically two one metre wide lanes for the running gear - but the civil engineering requirements for the crane rail foundations are quite impressive, with static wheel loads of up to 30 tons. Crane track length (net) would vary 100-750 m, with some 30m extra for running gear length and emergency braking equipment.
The loading and unloading cycle is somewhat longer than with the reachstacker (1.5 to 2.5 minutes), but the number of lanes served is considerably greater, e.g., up to a total of nine tracks, road lanes and storage lanes between the running rails and two more lanes outside the crane rails, either on one or both sides, adding up to some 60 metres. Even wider movement coverage areas are in use for ship loading, with partly automated operation.
Operation of electric cranes minimises noise and pollution.
Transfer of used cranes to a different location is rarely possible because crane rails would generally differ in gauge.
Crane construction comes in two main types: truss girder and box frames. Box frames are easy to produce and their welding lines can easily be checked. Truss girder frames necessitate a high standard of proficiency in manufacture and examination, because of the many, circular elements connected at three-dimensionally oblique angles. Their main advantages are less girder weight and lower air resistance forces which in turn allow construction with less overall weight, leading again to savings in lower steel usage, lighter foundation construction, and lower operational costs, mainly concerning energy consumption.
Box frames can come in different shapes as well. A lozenge shaped main frame for example, with an underslung single running beam might reduce crane weight, when compared to the standard, right angle construction.
Generally, cranes have a rotating crab running on top of lateral main crane girders and are equipped with a spreader and bottom lift equipment supported from wire ropes, some of which are hung at an oblique angle to suppress horizontal movement of spreader and unit. The lateral sections of the main crane outboard of the running gear are described as cantilever arms. Lift height is usually at about 10.5 metres, allowing to lift one container over three others. Heights of up to 14m may be provided to allow higher stacking.
(5 c) Rubber-tyred gantry cranes reduce the space requirements and improve parked load unit numbers compared with reachstackers and offer greater flexibility than gantry cranes. These cranes exist in an electrically driven form or with a diesel engine, the latter version allowing to serve segregated areas because wheels may be steered. The running gear always limits the lateral movement of lifting gear and load units.
This is a crane type that can be used to serve a small-throughput terminal with just a pair of short tracks; with added demand, tracks can be lengthened or another track element can be added. This crane type is generally operated from a hand-held control panel, i.e., without an operator’s cab.
(5 d) The spreader is the load grab unit allowing the lifting of containers of different lengths using the twist locks on top while bottom lift prongs can be used for swap-bodies and intermodal semi-trailers.
The operator cannot see the load grip elements and appreciate their proper functioning, so that electric sensors check safe status and visualise the status via coloured lights.
The need not to damage the trailer or swapbody and the necessity to grip the load safely unit requires a lot of hydraulic equipment and a decent number of joints.
(5 e) Terminal tractor are specialised tractors for the transport of semi-trailers within terminal confines, to allow the use of additional parking areas not served by gantry cranes.
6) Alternative systems
(6a) The Rolling Highway (Rollende Autobahn - Rollende Landstrasse) business is a completely different matter. This rail transport type is currently only employed over a very restricted number of routes, most of them crossing environmentally sensitive areas.
This restriction of usage is mainly due to the rather low percentage of allowable payload and the very specialised nature of the rail equipment with very delicate small diameter wheels.
(6b) The Eurotunnel service to public road vehicles is another similar service allowing any standard sized road vehicle to be carried by rail, to avoid combustion engine pollution in the "environmentally sensitive area" of the Channel Tunnel.
(6c) Various makes of road vehicles are available which can pick-up a container from the rail wagon and carry the unit along public roads at standard speed and set down the unit at the customer’s premises. This technology works without any preparation necessary on the rail side of the business: a short track section alongside a road vehicle carrying surface suffices. The drawback of this top-lift solution is the heavy weight of crane machinery carried around with the lorry.
(6d) Then there are lorries available which can move the container horizontally between wagon and road vehicle, but can not set down the unit at road level. This bottom-lift system requires non-standard mobile units.
(6e) Some wagon prototypes are available (and some types already withdrawn) that allow standard semi-trailers to be put onto wagons without the need to lift the road vehicle. The particular technical facilities of the wagons need special operators besides the lorry driver, so the running costs counteract the lower construction costs.
(6f) Finally the very special systems include many older approaches to intermodal business, some outdated and some newly invented, which are outside the scope of space available here. Some of these systems allow:
- carrying rail vehicles of different rail gauges,
- carrying rail vehicles on public streets,
- containers to be picked up from street level using a hydraulic "back hook" system.