It thus became the first French tram-train line, an event whose true significance emerged during plans to expand it into a tramway and integrate it into the urban transport network.

However, they failed to make the line more appealing to potential users, who remained uninterested because of its insufficient service level and the excessive length of the train's route.

The work aimed to:[5] The evolution toward urban transport modes was accompanied by physical modifications to the rail line by: Construction began in June 2004.

The entire track was removed and reinstalled, the stations' platforms were demolished and rebuilt, the 25 kV catenary was rewired, and the Gargan-Aulnay section was made into a double-track.

Six months later, in January 2006, the biggest operation took place in front of many onlookers: the new double-track overpass' walkway was installed overnight after traffic was blocked on the ex-RN3.

This would allow passengers to reach this multimodal hub and connect with the T1, the RER E (both the Tournan and Chelles-Gournay branches), the Tangentielle Nord, and a fortiori toward Paris.

On its initial day, 18 November 2006, two trains had damaged brakes, which caused the SNCF to interrupt service during the late afternoon, forcing many users to continue their trip on foot or by hitchhiking.

The frequent use of audio warning devices by train operators caused friction between nearby residents and elected officials on the one hand and the SNCF on the other.

This nuisance led to the creation of a collective of residents and local politicians who successfully reduced the volume of the audio devices by 15 dB in mid-March 2007.

Some pedestrian walkways remained inaccessible a year after the line opened; disabled people were unable to access certain points because of stairs; and the number of arches to store bicycles in the proposed shelters were reduced.

A group supported by the municipalities was able to save Les Coquetiers and L'Abbaye stations, but the L'Allée de la Tour Rendez-Vous building was destroyed.

The mayors did not want to oppose the electorate, who were unwilling to deal with the nuisances that would be caused by the expansion (noise, traffic, and the proximity of the plateau's disadvantaged population to their homes—particularly young people from housing estates).

This political impasse led to the publication of a leaflet[citation needed] and a protest by the plateau's elected representatives on the day of the tram-train's inauguration by officials.

According to him, this proposal would have both solved the public transportation issue in the Clichy-Montfermeil plateau and dealt with the congestion on the route nationale that packed buses travelled with difficulty.

The STIF's T Zen 3 project, a bus rapid transit service, was selected to improve public transportation in the communes crossed by the former RN3 from Porte de Pantin to Les Pavillons-sous-Bois.

[19] Fadela Amara, Secretary of State for Municipal Affairs (2007–2010), traveled to Clichy-sous-Bois on 9 November 2007, by RER and bus from Paris so she could assess the length and quality of public transportation from the capital.

"[14] The vice-president of the Region (1998–2010) and the STIF, Serge Méry, thus asked the French government to finance 30% of the project's cost, which would allow work to begin in 2011.

However, the Livry-Gargan commune requested that the CNDP present all the proposed routes created during the feasibility studies at the preliminary public debates and discussions.

The STIF decided to proceed with studies and consultations based on the two most appropriate proposals (no 3 and no 4), both of which included a branch toward Bondy, to analyze the consequences on the line's operations and automobile traffic.

Les Pavillons-sous-Bois, Livry-Gargan, Clichy-sous-Bois, and Montfermeil were chosen because they would be crossed by the new infrastructure, while Villemomble, Le Raincy, Bondy, and Noisy-le-Sec (for access to its maintenance and storage facilities) were selected because they would be affected by the doubling of the T4's service at the Bondy-Montfermeil connection.

[29] This 6-kilometre (3.7 mi)-long route includes eleven new stations built on average of every 400 to 600 metres (1,300 to 2,000 ft); an estimated 38,000 passengers are expected to travel daily along the section between Bondy and Montfermeil.

It entrusted part of the project ownership to:[citation needed] Work on the branch was originally planned to have commenced at the end of 2014, with the eventual commissioning to occur in 2017.

However the opening was postponed ultimately to 2019, due to the delay in the completion of studies and the need to carry out additional work at Bondy station causing continual extensions of deadlines.

The conversion of traction to 750V takes place gradually about 2 km (1.2 mi) along the branch from Gargan because several hundred meters are required for the lowering of the pantograph and the conduction of the current.

The line is also the first in France to use the GSM-R communications system, a standard ground-train radio link that is progressively being implemented throughout the French rail network.

After it reaches Gargan Station, which is located between Louis-Pasteur and Roy Boulevards, it travels up the former RN3 overpass, now known as Aristide-Briand Avenue, before returning to ground level again.

It makes a stop at Rougemont-Chanteloup Station then reaches the La Plaine à Hirson line near the bifurcation at Roissy and runs along it for a few hundred metres.

Service can occasionally be maintained continuously for twenty-four hours during important events such as the Fête de la musique or New Year's Eve.

Units sport the livery of Île-de-France Mobilités, the organisation ultimately responsible for the Montfermeil extension, of white & silver with celeste trim.

The T4 also has twelve urban train dispatchers overseen by three department heads and seventeen managers, and a dozen employees to maintain the cars at the Noisy-le-Sec shop.