Railway and Railroad transport systems: Tramway (part 2)





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(cont. from part 1)

4. INTEGRATION OF TRAMWAY CORRIDORS ACROSS THE ROAD ARTERIES

4.1 Types of integration of tramway corridors

The integration of at-grade tramway lines within the right of way can take place in different ways depending on the geometric and traffic characteristics of the road and the nature of the roadside land uses. More in particular


FIG. 16 Placement of a single tramway track at the two opposite sides of the roadway.


FIG. 17 Placement of a double tramway track on one side of the roadway.


FIG. 18 Placement of a double tramway track in the middle of the road using central electrification mast.

4.1.1 A single track per direction at two opposite sides of the road

This option is more appropriate for roads that operate as one-way roads for all other traffic.

Its main advantages are as follows (FIG. 16):

• In the case of an overhead power supply system, masts can be installed on the side footpaths. As a result a smaller right-of-way is required.

• At the stop areas, the existing sidewalks may well serve as part of the platforms.

Its main disadvantages are as follows:

• A noticeable difficulty in feeding the adjacent land uses, which necessarily takes place during specific hours of the day, especially during hours when the tram stops operating or operates with very low frequencies.

• In the case of small building blocks, the increased number of intersections can reduce the travel time savings, which come as a result of the segregation of the tram from all other traffic.

4.1.2 Double track on one side of the road

In this case, in the vicinity of the tramway stops, it is required to build an islet in order to create a platform for the second vehicle. As a result, the road width is reduced. This problem can be solved by creating a recess, which, however, reduces the width of the sidewalk (FIG. 17).

This is the simplest and least space-consuming integration, however, it has some negative impact on the local residents and their activities. In the case of small building blocks, the successive intersections with right-turning movements can reduce the travel time savings, which come as a result from the segregation of the tram from all other traffic.

4.1.3 Central alignment

The tramway system is located in the center of the right-of-way, usually in double track superstructure (FIG. 18). With this integration, there is no problem with turning road vehicles movements. In the case of overhead power supply, the integration of the tram in the center of the road artery may be implemented in two ways:

• Without electrification masts between the two tracks: In this case, the power supply of tramway vehicles is achieved through wires, which are suspended on laterally-opposed masts or connected to building facades. This integration offers a smaller right-of-way.

• With electrification masts placed centrally between the two tracks (FIG. 18): This solution is preferable in terms of aesthetics, but it is more expensive and least favor able for the road traffic as it requires greater corridor width.

The main advantage of placing the tramway system in the center of the road is the ease of access and feeding of the adjacent land uses, especially in the case of two-way traffic roads where positioning the tramway system at the two opposite sides of the road would significantly impede their operations.

The main disadvantage of placing the tramway system in the center of the road is the risk regarding the crossing of the rest of the road by pedestrians. In order to alleviate this risk, the construction of an islet with a width of 2.0m, is required at stops to ensure the comfort able and safe boarding and alighting of passengers. This, however, has an obvious negative effect, namely the reduction of the road width at these locations.

4.2 Geometric features of the integration of tramway corridors

In order to decide on the integration type of the selected categories of tramway corridors (classes A, B, C, D, E) it is essential to investigate the adequacy of the geometric features of the road in relation to the geometric features which are required for each case for the operation of the tramway system.

4.2.1 Technical and total tramway infrastructure right-of-way

The term technical right-of-way describes the minimum width required for the safe operation of the tramway system. For line segments between stops (the 'plain line') technical right-of-way is defined by the number of tracks, their gauge, the width of the dynamic gauge of tramway vehicles and the civil engineering structure gauge.

Depending on how the tram is integrated across the road artery, the technical right-of way of the tramway system should be increased either on both sides or on one side only, by such a distance that allows for the installation of separators between the tram and the rest of the traffic.

The final resulting width is called Total Tramway infrastructure technical Right-Of-Way (TTROW). Concrete bollards with a height of 15-20 cm, and a width of 40 cm or greater (minimum width 30 cm) where plants are dibbled may be used as means of segregation.

These bollards may also be used for posting signs or signals, which will serve the signal ling not only of the tramway system but also of other traffic. If the width of these bollards is greater than 1.20 m they can be used as intermediate stops for pedestrians during their movement on the level crossing. Apart from these segregation means, hatched lane (with a width of 40 cm), railings, wall separators, trees and so on, can also be used, depending on the type of integration of the tramway system in the road.

4.2.1.1 Total Tramway infrastructure technical Right-Of-Way at Straight segments of the alignment (TTROWS)

In the case of double track, at straight paths, the structure gauge is equal to the dynamic gauge of vehicles increased by 100 mm at either side of the double track, and by 200 mm between opposite moving tram vehicles.

The mathematical relationships that can be used in order to calculate the TTROWS for different ways of integrating tramway corridors across the road arteries, and depending on the category of tramway corridor, are shown hereunder.

1. Placement of a double tramway track at the center of the roadway (central alignment)

TTROWS2 b1 gb 2classes CD sw dv em =× ++ ++ (. ). (, ,, ) 00 ?? (eqn.1)

TTROWS2 gb 4class dv em =× ++ 0. () ? (eqn.2)

whereas bsw: Width of separator gdv: Dynamic gauge width of tram vehicle bem: Width needed for the installation of electrification masts

In case no electrification mast is foreseen, bem = 0

2. Placement of a double tramway track on one side of the roadway

TTROWS2 1g bb 2classesC D dv em sw =× ++ ++ (. ). (, ,, ) 00 ?? (eqn.3)

TTROWS2 gb 4class dv em =× ++ 0. () ? (eqn.4)

In case no electrification mast is foreseen, bem = 0

3. Placement of a single tramway track at the two opposite sides of the roadway

TTROWS2 b1 1g classes C D sw dv =× +++ (. .) (, ,, ) 00 ?? (eqn.5)

TTROWS2 2g class dv =× + (. )( ) 0 ? (eqn.6)

Table 7 provides the minimum values of the total tramway infrastructure right-of way which are required in order to integrate a tramway system across a road artery for a vehicle width of 2.30 m (dynamic gauge width gdv = 2.60 m), for a separator with a width of bsw = 0.40 m, for an electrification mast installation width of bem = 0.30 m, and for corridor categories A, B, C, D.


Table 7 Total infrastructure right-of-way values for a tramway system straight path.


FIG. 19 Inscription of a railway vehicle in curves. Definition of end/center throw.

4.2.1.2 Total Tramway Infrastructure Right-Of-Way in Curves (TTROWC)

A larger right-of-way is required in curves, and this is due to the following reasons:

• Primarily, it is due to the extra space required, because of the geometry, for the integration of the tracks across the road.

This extra space depends on the angle between the two intersecting roads and on the type of integration of the tramway line across the road before and after the intersection. In this context the required right-of-way of the tramway lines can be related and be expressed via the minimum required width of intersecting roads.

• Secondly, it is due to the effects of vehicle end throw on the outside of a curve and center throw on the inside of a curve (Figures 19 and 20). These reach their greatest values in the middle of the circular arc of the curved segment.

They directly depend on the length of the cars of the articulated tramway vehicle (they increase as the length increases).

Engineers can estimate the right-of-way at turns through appropriate design simulation.

FIG. 20 Inscription of a double articulated tramway vehicle in curves. Effects of vehicle end and center throw.

4.2.2 Geometric integration of tramway corridors at curved sections of roads in the horizontal alignment

The geometric integration of a tramway corridor in curved sections of the right-of-way requires the horizontal alignment of the tram, including considerations for end and center throw, to be able to match the horizontal alignment of the road artery and space constraints of the right of way in general; a minimum radius of horizontal alignment equal to Rcmin = 25 m is the usual minimum value considered.

A design simulation for all possible combinations regarding the integration type of the tramway track before and after the intersection, for intersection angles that vary between fo = 90° and fo = 170° has been developed in the literature. For this simulation, the following were considered:

• Static vehicle width equal to 2.30 m and dynamic vehicle width equal to 2.60 m

• Curve radius in the horizontal alignment Rc = 25 m (minimum permitted)

• Integration without central electrification mast

• Right turn and left turn

• At the area of the turn, the tramway corridor is common (class E)

The design simulation provided the minimum required road widths b1 and b2 of the road arteries. Table 8 presents the indicative results for all possible combinations of integration of the tramway track, for intersection angle fo = 120°.

Regarding the symbols used for the integration type (column 1 of Table 8):

• The first letter indicates whether the corridor is exclusive for trams or whether the use by other road vehicles is also permitted (classes B, D). More specifically, the following symbols are adopted:

C: Corridor class C (exclusive tramway corridor without use by other road vehicles)

F: Corridor class B and D (protected or separated tramway corridors)

• The second letter indicates the integration type of the double tramway track. More specifically the following symbols are adopted:

A: Integration of the track at the left side of the road

C: Integration of the track at the right side of the road

K: Integration of the track in the middle of the road

• The number 1 refers to single track, whereas the number 2 refers to double track

• The letter a indicates left turn movement, whereas the letter d indicates right turn movement

• Finally, the symbol X indicates that integration is not possible

As an example, the symbols F2?-F2K (d) indicate transition by a right turn, from a tram way corridor category B or D, with a double track placed at the right side of the roadway to a tramway corridor category B or D, with a double track placed at the center of the roadway (FIG. 21).

In order to enable the geometric integration of the tramway tracks at turns, even with the smallest allowable radius of 25 m, the two intersecting roads must have the available width that is calculated by following the procedure described above.

Table 8 Integration of a double tramway track in curved sections of the roads in the horizontal alignment - Required roadway width for road intersection angle fo = 120°


FIG. 21 Types of integration of double track tramway corridors across the road before and after the turn.


FIG. 22 Stop with center (island) platform.


FIG. 23 Stop with laterally staggered platforms.


FIG. 24 Stop with laterally opposed platforms.


FIG. 25 Tramway stop at Athens, Greece.

5. INTEGRATION OF STOPS

5.1 Types of stops integration

Terminals and stops constitute an important component of the tramway system. They are considered as structural elements of the tramway infrastructure and they fall under its operational facilities. Their presence in the system is necessary because they allow for the boarding and alighting of passengers to/from the trains.

Three categories of tramway stops may be considered:

• Stop with center (island) platform (FIG. 22)

• Stop with laterally staggered platforms (FIG. 23)

• Stop with laterally opposed platforms ( FIG. 24)

The level of service provided to the users of a tramway system at stops is determined by the degree to which certain parameters are satisfied. The key parameters (quality parameters) which reflect the user needs are:

• The acceptable distance between successive stops

• The location of stops at areas where land uses constitute attractors of a large number of trips

• The required halt time

• The accessibility of the stop

• The ability for quick transfer to other modes of public transport

• The service of people with reduced mobility

• The safety and comfort of passengers while waiting at the stops (seats)

• The information regarding the route and the next train arrival available for passengers

• The easy supply of tickets

• The interfaces between staff and users

• The easy identification of the stop from afar

• The protection of users against bad weather conditions (shelter)

• The aesthetics of the stop

• The attractiveness of the stop (surface integration, location at areas with recreational activities, retail or medical facilities)

A questionnaire survey among tram users in Athens revealed that the most important parameter for a tram stop is the available services in terms of land uses (preference 43%), followed by the ease of access to the stop (28%), and the adequacy of information and safety while waiting at the stop with percentages of preference equal to 12% and 11%, respectively.

Figures 25 and 26 illustrate a tram stop in the city of Athens, Greece, and Grenoble, France, respectively. This stop features a shelter, seats for the users, lighting, automatic ticketing machine, information display for the lines that serve the stop and waiting times in real time, route map, map of the area around the stop, closed circuit television(CCTV), separator between the stop and the other road traffic, accessibility ramp for the disabled and trash bin.




FIG. 26 Tramway stop facilities, Lyon, France.

5.2 Geometric and operational features of tramway stop integration

The location of stops and the choice of the type of platforms for a tramway network is based on the following geometric and operational criteria.

5.2.1 Geometric criteria

In the area of Stops, the required Total Technical Right-Of-Way (TTROWST) is larger than the respective technical right-of-way for a 'plain' line, due to the presence of platforms.

The minimum allowed width for a central platform is 2.50 m, while the minimum allowed width for a side platform is 2.00 m.

The mathematical equations that can be used for the calculation of TTROWST for different types of integration of tram stops, depending on the category of tramway corridor are shown below.

1. Installation of a tramway stop of a double track with center (island) platform

TTROWST 2b 1g b classes CD sw dv cp =× ++ + (. )( ,, ,) 0 ?? (eqn.7)

TTROWST 2(1g )b class E dv cp =× ++ 0. () (eqn.8)

...where bcp: width of the center (island) platform opposed platforms

2. Installation of a tramway stop of a double track with laterally opposed platforms

TTROWST 2b g2 classes CD E lp dv =× ++ () .( ,, ,, ) 0 ?? (eqn.9)

where blp: width of the side platform

3. Installation of a tramway stop of a double track with laterally staggered platforms

TTROWST b2 gb 3classes CD lp dv sw =+ ×+ + .( ,, ,) 0 ?? (eqn.10)

TTROWST b2 g3 class E lp dv =+ ×+ 0. () (eqn.11)

The length of the platforms must allow for the stopping of the tram of the greatest length.

Normally, and as long as is allowed by the length of the building blocks, the length of the platform should be at least double in order to allow for the stopping of two coupled trams during the peak hour.

5.2.2 Operational criteria

At intersections where full priority is granted to trams, it is preferable to install the stop after the intersection, so that the arrival time of the tram can be accurately estimated, as the stopping time largely depends on the time required for the boarding and alighting of passengers. This allows for the delay of the intersecting traffic to be minimized.

In case of an intersection where it is not desirable to give priority to trams, the most appropriate location of the stop is before the intersection, as the maximum delay time that can occur for the tram is equal to the length of the red phase of the light signal. Moreover, if the stopping time coincides with the red phase, there will be no delay.

For large uphill slopes it is preferable to place the tram stop at the end of the slope.

In case of curves with small radii, stops should preferably be located after the curve.

The distance between two successive stops should generally be greater than 400-450 m and less than 750-800m.

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Table 9 Facilities at a new tramway depot

Parking area/yard; Administration offices; Maintenance hall/workshop; Welfare facilities; Vehicle cleaning area; Waste storage; Warehouse (storage) area; Car parking space for employees and visitors; Painting workshop

6. TRAMWAY DEPOT FACILITIES

6.1 General description and operational activities

The depot can be considered as the heart of a tramway system. It is the starting point of all trams from which they commence their transport services for their passengers. In general, depots are spacious areas which accommodate the trains when they are not in timetable service. Maintenance (light or heavy) also takes place in the same area. This includes small scale repairs, sanding and cleaning.

The establishment of a new tramway depot is a tough procedure, since it takes place in an urban area with all the naturally ensuing problems. The main problem is finding a sufficiently large and available site; such large sites are rarely available inside the urban environment and are usually very expensive. Moreover, the selection of the location for the depot in an urban area almost always creates tensions and protests from neighboring residents.

The location and design of the depot significantly affects the overall operational cost of the tramway system. The depot should ideally be located as close to the tramway net work as possible, in order to minimize the dead vehicle kilometers. Furthermore, all of the involved installations and facilities must be designed optimally, since any wrong estimation can increase the time and cost of activities performed, thereby increasing the total operational cost.

Table 9 presents the facilities of a tramway depot. Painting workshop can be characterized as an optional facility.

The main design, constructional and operational characteristics of the essential facilities are presented in the following.

6.1.1 Parking area/yard

During the design of this area, the primary objective is to achieve the maximum tram parking capacity and a smooth flow of trains. The length of parking tracks depends on the number of trams which will park at each track, as well as on the tram's length. The lateral distance between parking tracks should be sufficient in providing a corridor of about 1.50 m between the sides of two parallel parked trams, in order to allow access by drivers, maintenance and cleaning staff. Thus, the size of the parking yard is the product of track length and track width, which depends on the number of tracks and their in-between distance.

Regarding the sheltering of the train parking area, there are three alternatives:

• Outdoor area

• Sheltered area (which features a roof with or without side walls)

• Indoor area (features a roof, side walls and a front/end wall and access doors)

6.1.2 Maintenance hall/workshop

This facility includes workshops for heavy maintenance, light maintenance, bogie maintenance, vehicle cleaning area, sanding plant, electronic systems unit, track maintenance (rails and catenaries), as well as facilities for the auxiliary equipment.

The length of each track depends on the length of the vehicles; normally, a maintenance track should be sufficiently long enough to service at least one tram.

The number of tracks depends on the number of trains that are served in the particular depot, on the multitude and type of activities performed within the light maintenance workshop and on the overall configuration, layout and utilization of the available space, maintenance-wise. In general, the maintenance facility area should be able to accept approximately 10% of the total number of trams normally served at the particular depot.

The lateral distance between two adjacent tram maintenance tracks should be sufficient in providing a corridor of about 3.5 m between the sides of two neighboring trams. Within this space, the maintenance staff may move, place the required mechanical equipment, and perform all necessary activities.

6.1.3 Vehicle cleaning/washing area

For the washing of trains in most depots, either the 'drive-through system' or the 'gantry system' is used.

Regarding the positioning of these systems inside the depot area, it is considered preferable to locate them along the route section which the train follows from the moment it enters the depot till it reaches the parking area. With this configuration, 'dead' mileage can be avoided, and the vehicle may also enter the maintenance halls if required, in a state facilitating inspection by the maintenance personnel. Furthermore, many depots locate their sand silos between the entrance and the parking yard, namely before the cleaning area.

6.2 Classification of tramway depots

Tramway depots are classified as follows:

• According to the means of transportation that they serve:

• Exclusively for tram use: Only tramway vehicles are served.

• Mixed use: Besides tram vehicles, other mass urban transit means, such as buses and trolleys, are also served.

• According to the activities performed within their area:

• Fully operating: All required activities are performed in the depot (see Table 9).

• Limited operating: A limited number of activities are performed. This may occur in two cases: in the first one, some activities are outsourced to third parties; in the latter case, the tramway system includes more than one depot and the required activities are shared among them.

• According to the depot's location within the network:

• Central: When the depot is located in the center of the network. This 'gravitational' location is preferred when the network follows a radial-shaped development.

• Terminal: When the depot is located at either end of the network. This position is preferred when the network follows a linear-shaped development.

• According to the size of the ground plan area:

• Very small: Serving up to 25 tramways.

• Small: Serving 25-35 tramways.

• Medium: Serving 35-65 tramways.

• Large: Serving more than 65 tramways.

• According to its accessibility from the main track:

• Through a junction.

• At the end of the main track as an extension.

6.3 Main design principles and selection of a ground plan area

The designer of a tramway system must be aware of the required area of the site during the early stages of the study so as to make an initial estimate of not only the cost of the tramway depot, but also the cost of the whole project. On the other hand, the operator needs to know in advance the required area of the site in order to proceed with their search and the procedures that will be required for its acquisition as quickly as possible (e.g., expropriation).

Currently, there are no regulated specifications for the design of a tramway depot. The literature references (Tramstore21, 2012a) and (Verband Deutscher Verkehrsunternehmen 823, 2001), provide the basic design, construction and operation principles without correlation with the train fleet (number of vehicles, train length). In this context, the design choices that are made and the final area of the tramway depot which they satisfy are governed by the initiative of the designers and the recommendations of the system operators. The cost of implementing a tramway depot is very high, and is around 20% of the infrastructure cost of a tramway system. The oversizing of the tramway depot increases the cost of the project significantly, while its undersizing results in problems in the system's operation.

The required area size of a tramway depot's ground plan depends on the following parameters:

• The fleet to be served (number of vehicles)

• The dimensions of the trains (length and width)

• The minimum allowed horizontal curve radius in the track alignment, and therefore, the geometric elements of switches and crossings

• The layout of parking and maintenance tracks for the trains

• The area size of main buildings and facilities

• The maintenance policy applied by the operator

In the initial fleet demand design, potential expansions should also be taken into account, regarding both the number of trams and their length, even mid-term.

It is recommended that the various facilities of the depot are interconnected. Additionally, the installation of a ring track (loop line), which circles around the area and is accessible from several points, is desirable. This allows trams to enter or exit the various facilities, such as the parking yard or the maintenance hall, without crossing through and occupying other areas. In general, the following routes should be possible without performing any maneuvers:

• Entry ? Parking Yard ? Exit

• Entry ? Inspection and Cleaning ? Parking Yard

• Parking Yard ? Inspection and Cleaning ? Parking Yard

• Entry ? Maintenance hall ? Parking Yard

• Parking Yard ? Maintenance hall ? Parking Yard

The warehouse (storage areas) should be located within or next to the maintenance work shop in order to reduce transfer times of the various materials. Administration offices, welfare facilities and the parking area for cars and motorcycles should be constructed at places where car and pedestrian movement do not conflict with operational tracks and tram movements.

Relevant literature proposes a methodology which allows the estimation of the minimum required area of the ground plan of the various installations of a tramway depot and its total area, in relation to the fleet, the length of the trains, the number and type of activities performed.

The whole approach is performed with the aid of two 'tools':

• Statistical data from existing tramway depots

• Design simulation of the required facilities and integration into an overall layout/plan The paper concludes with

• The formulation of simple mathematical expressions for calculating the useful area of individual facilities.

• The export of tables, which show the total area of the tramway depot.

• The configuration of the typical ground plans of the tramway depot sites which assign these findings for fleets between 15 and 80 vehicles, and train lengths of 30, 35, and 40 m.


Table 10 Example results from the design simulation - Estimation of the required area Ed of the tramway depot's ground plan for a fleet of 15-80 vehicles and for vehicle lengths of 30, 35 and 40 m

Table 10 provides example results of the design simulation of tramway depots for a fleet of 15-80 trains, and for vehicle lengths of 30, 35 and 40 m.

FIG. 27 illustrates the variation of the tramway depot's total ground plan area in relation to the fleet, for three different tram lengths.

FIG. 28 illustrates the variation of the tramway depot's total ground plan area in relation to the vehicle's length, for different fleet size.


FIG. 27 Variation in the total required ground plan area of the tramway depot in relation to the fleet, for different tram lengths.


FIG. 28 Variation in the total required ground plan area of the tramway depot in relation to the train length for different fleet sizes.

By studying Figures 27, 28 and Table 10, the following conclusions can be reached:

• The construction of depots for 15 vehicles (very small depots) requires an area of 30-35 acres.

• The construction of depots for 45 vehicles (medium depots) requires an area of 42-50 acres.

• The construction of depots for 80 vehicles (large depots) requires an area of 52-60 acres.



FIG. 29 Example layout of the configuration of a tramway depot for 45 vehicles with a length of 35 m.

FIG. 29 illustrates an example of a layout of the configuration of a tramway depot aiming to serve a fleet of 45 vehicles with a 35 vehicle length, as a result of a design simulation.

cont. to part 3 >>


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