Not too hot, not too cold: how can we maintain the right temperature for public transport?

Every day, we have to solve a complex equation: how to provide the best possible climate comfort for all our passengers while reducing energy consumption, which is one of our major objectives.

Last modified on 17 June 2025

4 min read

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Summary

Why does the heating remain moderate in the RER?

RATP works closely with Île-de-France Mobilités, which funds the renewal of equipment, to better integrate the impacts of extreme heat on the network.

For our travelers

The transition to increasingly air-conditioned or cooled equipment

The primary source of action lies in the modernity of the equipment, knowing that several generations of equipment coexist on the network as part of a gradual renewal. The most recent equipment is equipped with a refrigerated ventilation system or mild air conditioning.

Refrigerated ventilation : it cools the air inside the trains by a few degrees compared to the outside air temperature, providing travelers with a sensation of freshness and optimized comfort while being less energy-intensive than traditional air conditioning.
Air conditioning : it allows the interior air temperature to be regulated around a desired set point, independently of the outside temperature.

Find below the data of the current fleet.

Metro

METRO metro ligne 1 metro ligne 2 metro ligne 4 metro ligne 5 metro ligne 9 metro ligne 11 metro ligne 14

48% of the fleet is equipped with refrigerated ventilation (lines 1, 2, 5, 9, 11, and 14) and part of the fleet on metro line 4 (31 trains).

The rest of the fleet uses natural or forced ventilation with fans to create air movement. These systems, installed on older metro trains, are no longer considered satisfactory in the face of increasing heatwaves.

All future equipment (MF19), which will be deployed across the entire network between 2025 and 2036, will be equipped with refrigerated ventilation.

RER

RER rer ligne A rer ligne B

93% of the fleet is equipped with refrigerated ventilation;
On the RER A line: the MI09 and MI2N trains are equipped with refrigerated ventilation;
On the RER B line: all renovated MI79 and MI84 trains (84% of the fleet) are equipped with refrigerated ventilation. The MI84 trains are being equipped with refrigerated ventilation as they are renovated.
The future equipment (MI20), which will be deployed on line B between 2027 and 2032, will also be equipped with refrigerated ventilation.

Tramway

TRAMWAY tram ligne T1 tram ligne T2 tram ligne T3A tram ligne T3B tram ligne T5 tram ligne T6 tram ligne T7 tram ligne T8 tram ligne T10

The tram lines T1, T2, T3a, T3b, T5, T6, T7, T8, and T10 operated by the RATP for Île-de-France Mobilités are equipped with refrigerated ventilation.

Bus

The air conditioning of bus equipment has seen a significant acceleration in recent years, driven by Île-de-France Mobilités, with the gradual renewal of the RATP fleet to decarbonize it (for more information, see our article on the Bus2025 plan).

For example:
- In 2020, 5% of RATP buses were equipped with air conditioning;
- In 2022, 24% of RATP buses were air-conditioned;
- In 2023, 32% of buses are air-conditioned (1,485 buses or nearly 1/3 of the fleet);
- In 2024, 40% of buses are air-conditioned (1,861 buses or more than 1/3 of the fleet);
- By 2026, nearly 75% of buses are expected to be air-conditioned;
- By 2035, 100% of the fleet currently operated by the RATP for IDFM is expected to be equipped with air conditioning.

Mobilization of our agents in service of travelers

Every summer, an additional 250 people (known as "green vests") are recruited and trained to bolster our teams on the ground to assist and support travelers.

During periods of intense heat, our agents reinforce essential prevention messages.

In the event of a heatwave alert, RATP conducts operations to distribute water bottles and fans at 24 highly frequented points across the network, such as Bastille, Châtelet-Les Halles, and Marne-la-Vallée-Chessy. In partnership with Public Health France, preventive posters are also displayed in stations, stations, and buses.

Upcoming Deployment of Water Fountains on the Network

During heatwaves, staying hydrated is essential. Therefore, RATP will gradually deploy water fountains across its network.

30 fountains were installed during the summer of 2023. The objective is to install 90 fountains by the 2024 Summer Olympics.

To date, 81 fountains have been installed.

Infrastructure and Equipment

Infrastructure Monitoring

Heat isn't just a quality-of-travel issue for our passengers; it also affects our infrastructure. Indeed, high temperatures can impact our infrastructure and lead to disruptions in service (damage to cables, equipment shutdowns due to temperature thresholds being exceeded, etc.).

To minimize the risk of incidents during these extreme operating conditions, preventive maintenance measures have been strengthened over the years to enhance the resilience of our infrastructure.

For example, "heat patrols" are conducted to monitor tracks and detect any anomalies that could affect train circulation and railway safety. Since rails are particularly sensitive to temperature variations, rail temperature readings are taken daily between May 15 and September 15.

Regular surveillance routes on elevated tracks are also reinforced. Additionally, over the past three years, RATP has deployed around twenty connected sensors to monitor real-time rail temperatures on elevated sections of our network.

Special attention is also given to catenaries during the seasonal watch and is intensified during periods of high heat. RATP may decide to reduce train speeds or lower pantographs accordingly.

Rolling Stock Monitoring

Furthermore, regular preventive maintenance operations are carried out on rolling stock to prevent ventilation system failures during periods of high heat.

For rail equipment : Maintenance operations include replacement of filters, dust removal from evaporators and condensers, inspection of the cooling circuit and cleaning of water drains
For buses : Maintenance operations include, checking air conditioners and fans, replacement of filters, cleaning cooling radiators

Why does the heating remain moderate in the RER?

Since 2009, in most of our RER line A and B trains, the heating only cuts in when the temperature drops below 15°C, compared with 18°C previously. This measure contributes to an overall energy saving of between 5% and 30% depending on the train type, while ensuring better comfort for passengers, who dress according to the outdoor weather conditions.

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