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General information
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Description
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Whereas conventional stock consists of individual carriages resting on two
bogies each, in articulated trains consecutive cars rest on one shared bogie
connecting the two cars (LIREX and Copenhagen S-trains being an exception). In
articulated trains, cars are usually about 25% shorter.
Different realisations of articulated trains exist:
- Jakob-type bogies: Consecutive cars rest on a shared two-axle bogie.
- Single-axle bogies of the KERF type
- Talgo trains: consecutive cars rest on a single axle running gear located
between the two cars.
Figure 1 gives an overview.
The following evaluation refers to Jakob-type bogies being the most common
running gear for articulated trains. However, many statements are true for
articulated trains in general.
Figure 1: Different realisations of articulated trains
Source: IZT
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General criteria
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Status of development: in use |
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Jakob-type bogies are successfully used in many railways. Examples are TGV, IC3, Talent and Desiro. |
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Time horizon for broad application: now |
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(no details available) |
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Expected technological development: basically exploited |
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(no details available) |
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Motivation:
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Weight reduction |
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Benefits (other than environmental): big |
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Train design and passenger comfort Due to less train length car-bodies of articulated trains can be 10-20 cm wider than those of conventional trains for the same track and tunnel profiles. This improves seating comfort in 2 2 second class seating and allows to extend 2 2 seating (rather than 2 1 seating) to first class sections. Since car ends rest on joint bogies they do not sway out in curves. Due to this fact, interior car transitions can be designed to be wider than in conventional stock. Weight reduction Besides reduced energy consumption, weight reduction leads to higher acceleration rates for given traction power which is especially relevant in high-speed service. |
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Barriers: high |
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Infrastructure
Since articulated trains form fixed car sets and cannot be easily decoupled
into single cars, they put special requirements on the operator especially when
it comes to maintenance and repairs. For most articulated trains very long
maintenance workshops are needed (typically 150 m). This is one of the main
reasons, why countries like Germany and Switzerland are reluctant to introduce
main-line trains with Jakob-type bogies. However, depending on the existing
infrastructure of the operator and the actual length of the train sets, the
introduction does not always have to create major transition costs for the
operator (cf. General criteria - Example).
Flexibility of train composition
In addition, the fixed train composition leads to less flexibility in train
length. However, conventional MUs have the same restriction since traction
components are distributed along the train-set and therefore the train cannot be
decoupled into autonomous units. In both cases, the solution is to achieve
flexibility by having short train sets that may be combined to form trains of
variable length.
Axle load
Since the total weight is shared by less axles, articulated trains require
additional lightweight efforts in order to keep axle-load below 16
tons. |
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Success factors:
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(no details available) |
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Applicability for railway segments: high |
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Type of traction: electric - DC, electric - AC, diesel
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Type of transportation: passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines
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(no details available) |
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Grade of diffusion into railway markets:
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Diffusion into relevant segment of fleet: 5 - 20% |
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Share of newly purchased stock: (no data) |
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(no details available) |
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Market potential (railways): medium |
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In general, articulated trains offer a number of advantages, especially low weight. However, many operators fear high transition costs, at least in main-line fleet.
Nevertheless, there is a considerable market for stock with Jakob-type bogies. |
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Example:
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IC3 at DSB On a great part of their main line passenger service, DSB relies on the IC3, a diesel-mechanic train with Jakob-bogies. Before introducing the articulated train, it was checked if the workshops were prepared, especially as far as lifting of the whole train-set is concerned. Due to relatively short train-sets (59 meters), the transition efforts were limited. |
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Environmental criteria
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Impacts on energy efficiency:
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Energy efficiency potential for single vehicle: 2 - 5% |
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Energy efficiency potential throughout fleet: 1 - 2% |
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The main energy efficiency effect comes from reduced weight. General figures on the weight reduction effect through Jakob-type bogies are not available, but the following estimate illustrates the potential: - In a conventional EMU, the mass of the bogies accounts for about one third of the total train weight.
- The introduction of Jakob-type bogies reduces the ratio of bogies to cars by 30-50% (depending on train length).
- On the other hand, the car length is reduced by about 25 %.
- Therefore the number of bogies per train length is reduced by roughly 10-30%.
- Assuming that Jakob-type bogies have roughly the same weight as conventional bogies, this means that the weight of bogies per train length is reduced by 10 - 30%.
- This means a mass reduction potential of about 3 - 10 %, given that bogies account for about one third of the total train weight.
The following elasticity table gives the effect on overall energy demand for different types of operation:
| Traction | Brake energy recovery | Effect on train mass | Elasticity with regard to train mass | Effect on total energy consumption for traction | High speed train | electric | no | 3 - 10 % | 0,17 | 1 - 2 % |
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| yes | 0,12 | 0 - 1 % | Intercity train | electric | no | 0,19 | 1 - 2 % |
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| yes | 0,14 | 0 - 1 % |
| diesel | - | 0,19 | 1 - 2 % | Regional train | electric | no | 0,52 | 2 - 5 % |
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| yes | 0,44 | 1 - 4 % |
| diesel | - | 0,52 | 2 - 5 % | Suburban train | electric | no | 0,64 | 2 - 6 % |
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| yes | 0,57 | 2 - 6 % |
| diesel | - | 0,64 | 2 - 6 % | Range: | 0 - 6 % | Source: IZT |
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Other environmental impacts: neutral |
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Economic criteria
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Vehicle - fix costs: low |
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(no details available) |
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Vehicle - running costs: significant reduction |
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(no details available) |
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Infrastructure - fix costs: not applicable |
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Maintenance facilities Depending on the length of the fixed train-sets, maintenance facilities have to be extended. In high-speed transport articulated trains are typically 150 meters long and require corresponding workshops for maintenance and repairs. The transition costs are lower for the shorter train-sets used in local and regional transport. The Danish IC3 train-sets with a length of 59 m show that even in main-line transport short units can be used (of course in this particular case this possibility is owed to the special IC3 design allowing to fold away the driver cabins in order to create regular car transitions for passengers). |
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Infrastructure - running costs: increased |
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If longer maintenance halls have to be built, the costs for running these facilities are slightly increased as well. |
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Scale effects: none |
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(no details available) |
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Amortisation: not applicable |
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This strongly depends on the additional workshop infrastructure needed. If virtually no additional infrastructure is needed, there are no major additional costs to be paid back. |
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Application outside railway sector (this technology is railway specific)
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Overall rating
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Overall potential: promising |
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Time horizon: mid-term |
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Articulated trains are considerably lighter than their conventional counterparts. They have been used successfully for decades in all classes of passenger service. Short units of articulated trains used in local and regional service usually meet no major barriers. Longer units needed in main line and high-speed service often require additional buildings for maintenance and repairs. The corresponding transition costs represent the main barrier for articulated trains. Those operators not prepared for fixed train-sets should first exploit the potential for shorter articulated trains in local and regional transport and reconsider vehicle strategy in long-term. |