The is an electric multiple unit (EMU) train type used for commuter and outer-suburban services operated by East Japan Railway Company (JR East) in Japan since 2000.

Design

Trains were manufactured by Tokyu Car Corporation, Kawasaki Heavy Industries and also at JR East's factory at Niitsu in Niigata Prefecture.

The type evolved from the earlier 209 series and E217 series EMUs, with the main visible difference being wider bodies ( compared to the for earlier commuter trains), and the prototype train built in 1998 for trials on the Chūō–Sōbu Line was actually classified 209-950 series, later becoming E231-900 series. Full-production E231-0 series trains were subsequently introduced on the Chūō–Sōbu Line (10-car sets) and Jōban Line (10+5-car sets). Other variants include the 11-car E231-500 series for the Yamanote Line, and the E231-800 series with wide bodies and end doors for use on Tokyo Metro Tozai Line inter-running services.

From 2000 onwards, the first E231-1000 series outer-suburban variant was delivered for use on Utsunomiya Line and Takasaki Line services north from Ueno Station in Tokyo. These trains included transverse seating in some cars and were also equipped with toilets. Production continued into 2006 with trains delivered for use on the Tōkaidō Main Line south from Tokyo. From 2004 onwards, two bilevel Green cars were inserted into all E231-1000 series ten-car sets.

Variants / / E231-0 series: 5-car, 8-car, and 10-car sets used on the Chūō–Sōbu Line, Jōban Line, Narita Line, Musashino Line, and Keiyō Line E231-500 series: 10-car sets used on the Chūō–Sōbu Line (Soon Being Replaced by a new E235 series) E231-800 series: 10-car sets used on Chūō–Sōbu Line and Tokyo Metro Tozai Line inter-running services E231-900 series: 8-car set used on the Musashino Line and Keiyō Line E231-1000 series: 5-car and 10-car suburban sets used on the Tōkaidō Main Line, Utsunomiya Line, and Takasaki Line, and on Ueno–Tokyo Line and Shōnan–Shinjuku Line through services E231-3000 series: 4-car sets converted from former E231-0 series sets for use on the Kawagoe Line and Hachikō Line

Former operations E231-500 series: 11-car sets used on the Yamanote Line from 21 April 2002 until 20 January 2020 E231-900 series: 10-car set used on the Chūō–Sōbu Line from December 1998 until 25 February 2020 (designated as 209-950 series until June 2000)

E231-0 series

The first full-production E231-0 series trains were introduced on the Chūō–Sōbu Line between February 2000 and November 2001, with 21 ten-car sets (101–121) based at Narashino Depot in Chiba and 21 ten-car sets (20–25, 28–42) based at Mitaka Depot in Tokyo. They replaced older 103, 201, and 205 series trains. One more ten-car set (57) was delivered to Mitaka Depot in November 2002. In December 2003, all Narashino sets were transferred to Mitaka Depot and renumbered 1–19, 26, and 27. Between October and November 2006, three more sets (80–82) were built to replace three 209-500 series sets transferred to the Keihin–Tōhoku—Negishi Line, creating a total fleet of 46 trains. The Chūō–Sōbu Line sets each contained a six-door car.

New built E231-0 series sets were also delivered to Matsudo Depot between November 2001 and February 2005 for use on Jōban Line services between Ueno and Toride, and also Narita Line services to Narita, replacing the earlier 103 series fleet. A total of 17 ten-car sets (101–117) and 19 five-car sets (121–139) were built.

From December 2009 to November 2011, set 27 was temporarily transferred to Tokyo General Rolling Stock Center and used to deliver new SaHa E231-600 and SaHa E231-4600 trailer cars for the Yamanote Line. In 2012, a "B" suffix was added to all Chūō–Sōbu Line sets (B1–B42, B57, and B80–B82).

Refurbishment Between 2015 and 2020, all E231-0 series sets underwent a mid-life refurbishment with new equipment. In addition, with the transfer of former Yamanote Line E231-500 series sets to the Chūō–Sōbu Line and to prepare for the installation of platform doors, 40 trains were transferred from the Chūō–Sōbu Line to other lines, while six trains were reformed and remain on the Chūō–Sōbu Line with all six-door cars replaced with excess four-door cars from the other 40 sets.

In late 2014 and early 2015, two Chūō–Sōbu Line sets (B20 and B21, with six-door cars substituted by two trailer cars from B22) were transferred to the Jōban Line (and renumbered 118 and 119) for the extension of the Jōban Line services to Shinagawa Station with the opening of the Ueno–Tokyo Line. This brought the total number of Jōban Line sets to 38 (19 five-car and 19 ten-car sets), all of which were refurbished between 2015 and 2020.

From October 2017 to September 2020, 32 Chūō–Sōbu Line sets were refurbished, shortened to eight cars, and transferred to the Musashino Line (and renumbered MU2–MU21, MU31–MU39, and MU41–MU43) to replace older 205 series and 205-5000 series sets; the first set (MU2) entered service in November 2017.

From November 2017 to October 2019, six Chūō–Sōbu Line sets were refurbished, shortened to four cars, redesignated as E231-3000 series, and transferred to the Hachikō Line and Kawagoe Line.

The first reformed E231-0 series Chūō–Sōbu Line train (with 6 motored cars and no six-door car), numbered set B11 and composed of 8 cars of former set B11 and 2 cars of former set B5, completed refurbishment on 24 April 2018 and reentered into service on 21 May 2018. A total of six reformed ten-car trains remain on the Chūō–Sōbu Line. The last non-reformed trains (with 4 motored cars and a six-door car), sets B80 and B82, were removed from service after 13 March 2020.

Transfers from Chūō–Sōbu Line Chūō–Sōbu Line transfers and reformations (standard pattern) Old Chūō–Sōbu4M6T sets x41 Car 1KuHa E231 Car 2SaHa E231 Car 3MoHa E231 Car 4MoHa E230 Car 5SaHa E230 Car 6SaHa E231 Car 7SaHa E231 Car 8MoHa E231 Car 9MoHa E230 Car 10KuHa E230 Type cab + trailer trailer motored pair trailer6-door trailer trailer motored pair trailer + cab New Chūō–Sōbu6M4T sets x5 Car 1 X Car 2 Car 3 X Car 4 Car 7 Car 8 Car 9 Car 10 Hachikō/Kawagoe-3000 series sets x5 Car 4 X Chūō–SōbuCar 5 Chūō–SōbuCar 6 X X X Car 3 Car 2 Car 1 Musashinosets x31 Car 1 X Car 2 Car 3 X Car 4 Car 5 Car 6 Car 7 Car 8

Chūō–Sōbu Line transfers and reformations (non-standard pattern) Old Chūō–Sōbu4M6T sets Car 1KuHa E231 Car 2SaHa E231 Car 3MoHa E231 Car 4MoHa E230 Car 5SaHa E230 Car 6SaHa E231 Car 7SaHa E231 Car 8MoHa E231 Car 9MoHa E230 Car 10KuHa E230 Type cab + trailer trailer motored pair trailer6-door trailer trailer motored pair trailer + cab Former B5 Hae 41Car 4 X Mitsu B11Car 5 Mitsu B11Car 6 X Keyo MU2Car 4 X Hae 41Car 3 Hae 41Car 2 Hae 41Car 1 Former B11 Mitsu B11Car 1 X Mitsu B11Car 2 Mitsu B11Car 3 X Mitsu B11Car 4 Mitsu B11Car 7 Mitsu B11Car 8 Mitsu B11Car 9 Mitsu B11Car 10 Former B20 Mato 118Car 10 Mato 118Car 9 Mato 118Car 8 Mato 118Car 7 X Mato 118Car 5 Mato 118Car 4 Mato 118Car 3 Mato 118Car 2 Mato 118Car 1 ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ Keyo MU22Car 1 X Keyo MU22Car 2 Keyo MU22Car 3 Keyo MU22Car 5 X Keyo MU22Car 6 Keyo MU22Car 7 Keyo MU22Car 8 Former B21 Mato 119Car 10 Mato 119Car 9 Mato 119Car 8 Mato 119Car 7 X Mato 119Car 5 Mato 119Car 4 Mato 119Car 3 Mato 119Car 2 Mato 119Car 1 Former B22 Keyo MU2Car 1 Keyo MU2Car 5 Keyo MU2Car 2 Keyo MU2Car 3 X Mato 118Car 6 Mato 119Car 6 Keyo MU2Car 6 Keyo MU2Car 7 Keyo MU2Car 8 ↓ Keyo MU22Car 4

Lines served Chūō–Sōbu Line Jōban Line (Rapid) (Toride – Ueno), Ueno–Tokyo Line, Tōkaidō Line (Tokyo – Shinagawa) and Narita Line (Abiko – Narita) Musashino Line, Keiyō Line (also Musashino and Shimōsa)

Formations

10-car Chūō–Sōbu Line 6M4T sets (since 2018) , six ten-car sets (B10–B12, B14, B26, B27) are based at Mitaka depot in Tokyo and formed as shown below with six motored ("M") cars and four non-powered trailer ("T") cars.

   Car No. 1 2 3 4 5 6 7 8 9 10 Designation Tc M M' T M M' T M M' Tc' Numbering KuHa E231 MoHa E231 MoHa E230 SaHa E231 MoHa E231 MoHa E230 SaHa E231 MoHa E231 MoHa E230 KuHa E230 Cars 2, 5, and 8 each have one PS33B single-arm pantograph. Cars 1 and 10 have a wheelchair space. Car 4 is designated as a mildly air-conditioned car.

10-car Jōban Line sets , 18 ten-car sets (101–117, 119) are based at Matsudo depot in Chiba Prefecture and formed as shown below with four motored ("M") cars and six non-powered trailer ("T") cars.

    Car No. 10 9 8 7 6 5 4 3 2 1 Designation Tc T M M' T M M' Tc' Numbering KuHa E231 SaHa E231 MoHa E231 MoHa E230 SaHa E231 MoHa E231 MoHa E230 KuHa E230 Cars 3 and 8 each have one PS33B single-arm pantograph. Cars 1 and 10 have a wheelchair space. Car 8 is designated as a mildly air-conditioned car.

5-car Jōban Line sets , 19 five-car sets (121–139) are based at Matsudo depot in Chiba Prefecture and formed as shown below with two motored ("M") cars and three non-powered trailer ("T") cars.

    Car No. 15 14 13 12 11 Designation Tc T M M' Tc' Numbering KuHa E231 SaHa E231 MoHa E231 MoHa E230 KuHa E230 Car 13 has one PS33B single-arm pantograph. Cars 11 and 15 have a wheelchair space. Car 14 is designated as a mildly air-conditioned car.

8-car Musashino Line sets , 33 eight-car sets (MU2–MU22, MU31–MU39, MU41–MU43) are based at Keiyō Depot and formed as shown below with four motored ("M") cars and four non-powered trailer ("T") cars.

     Car No. 1 2 3 4 5 6 7 8 Designation Tc M M' T M M' Tc' Numbering KuHa E231 MoHa E231 MoHa E230 SaHa E231 MoHa E231 MoHa E230 KuHa E230 Cars 2 and 6 each have one PS33B single-arm pantograph. Cars 1 and 8 have a wheelchair space. Car 4 is designated as a mildly air-conditioned car.

Previous formations

10-car Chūō–Sōbu Line 4M6T sets (2002 to 2020)    Car No. 1 2 3 4 5 6 7 8 9 10 Designation Tc T M M' T' T M M' Tc' Numbering KuHa E231 SaHa E231 MoHa E231 MoHa E230 SaHa E230 SaHa E231 MoHa E231 MoHa E230 KuHa E230 Cars 3 and 8 each had one PS33B single-arm pantograph. Car 5 had six pairs of doors per side. Cars 1 and 10 had a wheelchair space. Car 4 was designated as a mildly air-conditioned car.

Interior

Special liveries

In April 2021, to commemorate the 120th anniversary of the Abiko Branch Line, JR East recolored set 139 into Sōbu/Yokosuka Line blue and cream stripes. Initially, only the cab ends received the commemorative stripes; however, these stripes were later extended to the rest of the train's body. The trainset was painted back into its original livery in late October.

E231-500 series

A fleet of 52 11-car E231-500 series was delivered from January 2002 to April 2005 for use on Yamanote Line services, replacing the earlier 205 series fleet. The first trains entered service on 21 April 2002. These trains include digital automatic train control (D-ATC), and feature pairs of LCD passenger information screens above each door internally. These screens also show advertisements. Each 11-car set originally contained two six-door SaHa E230 trailer cars (cars 7 and 10) with six pairs of doors per side and bench seats that were folded up until 10 a.m. on weekdays to provide standing room only during the morning peak. From 22 February 2010, the seats were able to be used during the morning peak.

SaHa E231-600/-4600 series cars To standardize door spacing ahead of the introduction of platform doors on all Yamanote Line stations by 2017, the two six-door cars in each set were subsequently replaced by a new build of four-door trailer cars between February 2010 and August 2011, the first of which were delivered from JR East's Niitsu factory on 1 February 2010.