Coupled-set Light Rail Vehicles

A mixed phase coupled set, consisting of a Phase I and and Phase II-T LRV

The Coupled-set Light Rail Vehicles, originally referring to one cab unit remotely controlling another attached to it, there is also power when running normally), and later extended to train formations with more than one car. When a dual-carriage train arrives at any stop, passengers in both compartments can enter and exit at the same time through all doors. Therefore, operations are more efficient compared to two separate LRVs, and the frequency is more punctual, which helps to improve the overall operational efficiency and passenger capacity. However, for some short distance special services, a single car may be used to better manage resources.

History

Before KCR West Rail opened to traffic, coupled-sets were mainly concentrated on the long-distance 614, 720, 721 route, taking the morning rush hour on weekdays in August 2003 as an example, of 12 total services, 7 are coupled-sets, and even all trains on route 720, 721 are coupled-sets. When a coupled set LRV is operating in revenue service, both LRVs are connected to power and commands are managed through a multi-functioning coupler.

When a dual-carriage train arrives at the station, passengers in both compartments can enter and exit at the same time. Therefore, it is more efficient than two single-carriage trains, and the frequency is more punctual, which helps to improve the overall operational efficiency and passenger capacity. As for single-car vehicles, it is easier to deploy flexibly; generally speaking, short-distance special shifts are mainly single cars, effectively increasing the number of shifts and increasing the passenger capacity.

Application

Phase II and V trailers (12xx) do not have cabs, except a hidden set of hostler controls for non-revenue use

In revenue service, Light Rail trains can be run with up to three LRVs in a set, with some platforms designed for this (intended as express services between major interchanges and some busier stops). Since most platforms can only accommodate up to 2 cars in a set, the maximum length is two cars per train. In case of an emergency, for example, when a LRV or coupled set breaks down between stations and the next available train to assist is two cars, a three car or four-car set may be formed. Sets with more than two cars can also be formed for testing and non-revenue equipment transfer runs. However, all trains with more than two cars are never in revenue service.

The main function of coupled sets is to increase the train capacity while the overall number of shifts (too many shifts will lead to congestion at major interchanges) and the number of train lengths required remain unchanged. At present, dual-carriage trains account for about 49% of the total number of trains. According to on-site inspections of the MTR during peak hours, an individual LRV can actually carry up to about 200 passengers, that is, a coupled-set LRV can carry up to about 400 passengers. In addition, the now retired Phase IIT and the current Phase VT (12xx trailers) have hidden hostler controls instead of a cab, freeing up more space for passengers. They can also be distinguished by not having a LED display on the front of the vehicle.

The highest passenger load rate of each light rail route mainly occurs within about an hour in the morning (the busiest hour of different light rail routes is slightly different). Now the distribution of single and double cars may not be even during peak hours. If the route is mixed with single cars and coupled sets, the congestion of each shift will be uneven, thus a waste of resources. On the contrary, in other time periods, the distribution of passenger waiting time is relatively average, the frequency of trains is relatively stable, and the distribution of single-cars and coupled-sets is relatively average.

After careful consideration of the passenger capacity of each Light Rail route, passenger travel patterns and the busy sections of individual routes, the MTR Corporation has formulated the arrangements for the deployment of Light Rail vehicles. The regular schedules of the 12 light rail routes during peak hours were once divided into the following three categories:

• The whole route is operated by double-car trains (with some exceptions):Light Rail Routes705, 706, 761P
• Mixed operation of single-car and double-car trains: Light Rail Routes 505, 507, 610, 751
• Most of the trains on the whole route run with one LRV: Light Rail Routes 614, 614P, 615, 615P
• The whole route is operated by single LRVs: Light Rail Routes 507P, 751P

As the density of light rail frequency affects the frequency stability, especially at busy intersections, the MTR Corporation changed the light rail timetable again on June 29, 2019 to reduce the frequency and increase the number of coupled sets to relieve the light rail traffic. Congestion problems, among which 614, 615, 751P frequency reduction is the most significant. However, after the revision of the timetable, the number of vehicles on the 614 route has not decreased but increased, and the proportion of shifts requiring a double set have increased to half the time.

In April 2021, MTR submitted a document to the Working Group on Collective Transport Services of the Yuen Long District Council, mentioning the distribution of the number of trains for each route of the Light Rail system.

Arrangement of single/dual card for each route of Light Rail during peak hours from Monday to Friday in 2020
Light Railroute	Number of single-car trains	Number of double-card trains	total number of vehicles
505	2	5	12
507	7	3	13
610	7	5	17
614	5	1	7
614P, 615P	10	0	10
615	4	2	8
705	0	5	10
706	0	6	12
751	5	7	19
751P	2	0	2
761P	0	12	24
Total	42	46	134

Note: MTR pointed out in the document that the number of LRVs used are based on the data taken in the months when the epidemic situation was relatively mild. Compared with the operational data, it should refer to the period from mid-September to early December, when schools resume classes.

The coupled-set service frequency will change with the short-term passenger volume changes. For example, when there is a large-scale event, some routes may be assigned two car trains to run services normally operated with a single car to better handle increased volume; on the contrary, when the passenger volume is reduced due to epidemic or school holidays, some two-car trains may be rescheduled to run with a single LRV.

Limitations and Safety Issues

Due to the difference in acceleration with the traction motors, under normal circumstances, the Phase I LRV can only run in parallel with units in the same class or Phase II (including 2T), while they cannot be combined with Phase III, Phase IV or Phase V LRVs, and vice versa, so that the scheduling of the vehicles is limited; also due to different door speeds between Phase I/II and newer sets. Phase III LRVs are also unable to operate in service with a Phase IV or V LRV.

In addition, since the refurbishment of the Phase I LRVs, they were no longer combined with the Phase II LRVs (or non-refurbished phase I LRVs), which means that all light rail trains will only run in service with a classmate. However, this is not the case when a LRV breaks down and needs to be pushed or towed back to the depot or during test runs. In these cases, if a Phase I is used to tow or push a newer LRV or vice versa following the retirement of the Phase II LRV, the unit(s) being towed or pushed cannot be connected to power, unless an operator is in the cab of the unit being towed. A LRV involved in an accident or collision, will also not be connected to power while being pushed/towed, regardless of the vehicle used to push or tow it.

Due to platform limitations at most stops, there are no consists in revenue service that are operated with more than two LRVs. Coupled sets that are longer than 2 LRVs are only operated outside of revenue service or in an emergency without passengers onboard.

When a LRV is run with a trailer, the second car affects the flexibility of operation, and the time spent turning is longer when running through a curve, so it takes longer to operate some routes. In addition, due to the swing radius of the coupler when negotiating sharp curves (especially S turns), the curvature limit is higher than that of a single car. All trains on Route 705 are allocated Phase III, IV and and V LRVs are because Phase I and II LRVs (including 2T) have a higher risk of uncoupling through the S-shaped bend of platform 1 at Tin Shui Wai Station. However, on September 17th, 2018, a Phase I LRV set was running on Route 705; and December 28, 2020 also had Phase II LRVs run on Route 705.

Because of these complications, the Light Rail system has had many incidents of accidental opening of the doors, particularly with double car sets. If a single car is stopped on a platform only able to accommodate two cars and a double car LRV pulls in behind, the doors of the trailing car would open outside of the platform.

Among them, at about 7:30 am of September 22 2009, a Coupled-Set of LRVs running on route 610 to Tuen Mun Ferry Pier stopped at the wrong position at Hong Lok Road Stop (it stopped at the second half of the platform behind a single car) and the driver opened the doors anyways, causing the trailing car's doors to open outside of the platform. The driver in question was unaware that they were operating a double car LRV.

On 3 September 2011 and 12 August 2014, similar incidents occurred.

In order to prevent such accidents from happening again, MTR Corporation later required all Light Rail operators using a single car to wait at the front half of the platform. When a single car is stopped on any platform, the train behind (regardless if single car or coupled) must wait for the LRV in front to depart before entering the platform. As a general rule, if a LRV must stop partially outside of a platform to observe a stop signal, the doors also cannot be opened. Two single cars are no longer allowed to serve the platform of any stop at the same time (except when terminating).

External links

• http://www.discuss.com.hk/viewthread.php?tid=11258537&page