MI 79

The MI 79 (French: Matériel d'Interconnexion de 1979, English: interconnection rolling stock of 1979), also known as the Class Z 8100 is a dual-voltage electric multiple unit trainset that is operated on line B of the Réseau Express Régional (RER), a hybrid suburban commuter and rapid transit system serving Paris and its suburbs. The MI 79, designed in the 1970s for the RER B which needed dual-voltage (interconnection) trainsets. They were followed by a derivative version, the MI 84, designed in the 1980s to meet the needs of the RER A line, before reassigned to the RER B in the 2010s.

MI 79 (Class Z 8100)
MI 79R train at Laplace station on the RER B line.
In service	1997–present
Manufacturer	Alsthom and Société Franco-Belge
Constructed	1980–1985
Entered service	1980–present
Refurbished	2010–2015
Number built	120 trainsets (480 cars)
Number in service	116 trainsets (464 cars)
Number scrapped	4 trainsets (16 cars)
Formation	4 cars per trainset
Fleet numbers	Z 8101–Z 8340
Operator(s)	RATP
Depot(s)	Massy Mitry-mory
Line(s) served
Specifications
Car body construction	Aluminium
Train length	104.16 m (341 ft 9 in)
Car length	26 m (85 ft 4 in)
Width	2.8 m (9 ft 2 in)
Height	4.18 m (13 ft 9 in)
Doors	4 pairs per side, per car
Maximum speed	140 km/h (87 mph)
Weight	205,600 kg (453,300 lb)
Traction system	8x CEM/Oerlikon thyristor chopper self-ventilated motors per trainset
Power output	2,800 kW (3,800 hp)
Acceleration	3.3 km/(h⋅s) (2.1 mph/s)
Deceleration	5.0 km/(h⋅s) (3.1 mph/s) (emergency brake)
Electric system(s)	1.5 kV DC or 25 kV AC overhead catenary
Current collection method	Pantograph (type AX)
Braking system(s)	Disc and dynamic
Safety system(s)	EAS, KCVB
Coupling system	Scharfenberg type
Multiple working	MI 79 or MI 84
Track gauge	1,435 mm (4 ft 8 ^1⁄2 in) standard gauge

History

In the early 1970s, work was underway to create the Réseau Express Régional (RER), a hybrid suburban commuter and rapid transit system serving Paris and its suburbs. The RER B line would be created by connecting two existing lines with a new tunnel that would run from north to south through the heart of Paris.

This proposed line presented some complications. The Ligne de Sceaux to south of Paris, owned by RATP, had 1.5 kV DC electrification and platforms at a height of 105 cm (41 in), while the Chemin de Fer du Nord to the north of Paris, owned by SNCF had 25 kV AC electrification and platforms at a height of 55 cm (22 in).

The solution was a train capable of using both electrification networks ("interconnecting") with a pneumatically controlled exterior step that would stay at floor height at high platform stations and would be automatically lowered when entering low platform stations.[1] The MI 79 would be formed as four-car trainsets with a total length of 104 m (341 ft) which would allow two trainsets in multiple working to perfectly fit at the shortest platforms on the line which were 208 m (682 ft) long.[1]

As the SNCF and RATP would jointly operate the RER B, the agencies also jointly ordered the MI 79.[2] The contract to build the trainsets was awarded in 1979 to Alsthom and Société Franco-Belge (which would be acquired by Alstom in 1982, before the completion of the order). The initial order, called the MI 79A, would be for a total of 72 four-car trainsets: 31 to be purchased by RATP and 51 to be purchased by SNCF.[1] The first trainsets were rapidly assembled and the first trainsets arrived for testing in 1980.[1] The RATP made an order for 38 additional trainsets to be called the MI 79B which incorporated several improvements, including simplification of the coupler system, changes to the brake control system, and simplification of door controls.[2] All of the trainsets would be delivered by 1985.

Although the trains were needed to enable the interconnection of the RER B, technical issues with the MS 61, forced RATP to transfer 24 MI 79 trainsets from the RER B to the RER A to make up for a shortfall in equipment. An issue with the MI 79 was discovered during a cold wave in 1985–86, electrical components and motors did not have enough insulation. The retirement of the Z 23000 railcars dating from 1938 was postponed to make up for the shortfall in equipment caused by MI 79 trainsets sidelined with frost issues.[3]

A trainset was damaged in the 1995 France bombings and another was damaged in the 1996 Paris RER bombing. The undamaged trailer and motor cars from these sets were later combined.

The MI 79 trainsets underwent a major refurbishment project between 2010 and 2015 at a cost of €275 million. [4]

Design

Original MI 79 interior

As delivered, the MI 79 had an interior design in keeping with the aesthetics of the time, including red and blue vinyl seats, cream-colored ceilings, yellow side walls, and dark blue end walls. Also, because the RER B would serve Charles de Gaulle Airport, trains were equipped with luggage racks above the seats.[1]

One of the design choices that would later present a problem was the flip-down seats near the entry doors. When in use, they obstruct part of the entryway, leaving a space only 40 centimetres (16 in) wide for passengers to board or disembark.[1]

The trainsets are light for their size and era of construction thanks to the use of aluminum for the body. Each four-car trainset is equipped with eight motors (one on motor per axle on the power cars) developing a total of 2,800 kW (3,800 hp). That combination of low weight and high power allows the MI 79 to fully depart from a 208-meter platform in 23 seconds and reaching their 140 km/h (87 mph) top speed in 100 seconds.[1]

Refurbishment

Refurbished MI 79 interior, showing luggage rack (left) and lean bars by doors

Between 2010 and 2015, the MI 79 trainsets underwent a major €275 million refurbishment project.[4] The project included some new electronic components for the traction power system, KCVB cab signaling, the addition of refrigerated ventilation (air conditioning),[5] but the most noticeable change in the project is the complete renovation of the interiors of the trainsets. Interiors now feature bright white walls, new gray and lime green seats. The problematic folding seats near the doors were removed and replaced with lean bars.[6] The luggage racks near the ceiling, which had proven inconvenient, were removed and replaced by luggage racks near doors and luggage storage areas under seats. The space near the ceiling, now freed up, was used to install ventilation ducts, video surveillance systems and the SISVE system of automated audible next stop announcements and dynamic route maps.[6] The project was delayed after asbestos dust was detected inside a refurbished trainset.[7]

Gallery

• 
  MI 79 in original "Île-de-France" livery at Cité Universitaire station
• 
  Refurbished MI 79 in new STIF/RATP/SNCF livery
• 
  Refurbished MI 79 underground at Denfert-Rochereau station
• 
  MI 79 with the step in the low position
• 
  Original MI 79 interior showing flip-down seats by doors
• 
  MI 79 interior showing the SISVE lighted route map

References

1. "MI79, pionnier de l'interconnexion". transportparis. 7 November 2014. Retrieved 22 January 2021.
2. Lecompte, Pierre; Boschat, Francis (September 1984). "Le matériel d'interconnexion MI 84". Revue générale des chemins de fer (in French). pp. 417–424.
3. "Les automotrices de la ligne de Sceaux". Transport Paris (in French). Archived from the original on 15 January 2021. Retrieved 15 January 2021.
4. "Le MI rénové montre son nez". MétroPole. 22 April 2010. Retrieved 2 February 2021.
5. "Tout sur le confort climatique dans les trains du RER B !". Le blog du RER B. 13 July 2017. Retrieved 2 February 2021.
6. "Le MI 79 "next-gen" en circulation". MétroPole. 6 January 2011. Retrieved 2 February 2021.
7. "Amiante du RER B : plus de 30 voitures touchées". Le Parisien (in French). 24 September 2011. Retrieved 2 February 2021.