Heatwave in Île-de-France: why is transport traffic disrupted?
How does the heat impact your public transport?
Live electrical cables = train slowdowns with the heat
Overhead electrical cables (called catenaries), which power a large part of the trains, trams and RER, are affected by the heatwave.
They can relax or break, causing power cuts and unplanned traffic stops during heat waves.
High heat means the risk of rail expansion
It is a natural phenomenon, when temperatures exceed 30 °C, the metal of the rails heats up and expands, reaching between 50 and 60 °C (when the outside temperature exceeds 37 °C).
This expansion can cause a slight deformation of the tracks, which can become dangerous if trains are travelling at normal speed. In places, the rails are painted white to reduce their temperature and limit expansion.
What measures are taken on traffic to guarantee your safety in the event of a heat wave?
Enhanced infrastructure monitoring
The technical teams that manage the day-to-day operation of the lines (SNCF and RATP) are mobilized to inspect the tracks and monitor the equipment in real time.
High temperatures = immediate adaptation of traffic
When temperatures exceed the 30 degree threshold:
- Speed limits are in place
- Trains can be cancelled or their circulation reorganised (when the rails have become too deformed)to maintain an optimal level of safety for passengers
Objective? Air conditioning for your journeys
To improve the comfort of your journeys, Île-de-France Mobilités is investing in equipping all its vehicles with refrigerated ventilation or air conditioning.
In June 2025:
- 100% of trams are air-conditioned in Île-de-France
- 73% of trains and RER trains have ventilation or air conditioning on board
- 57% of buses and coaches are air-conditioned
- 48% of metros are equipped with refrigerated ventilation or air conditioning. By 2035, 100% of the fleet will be equipped!
On your side: what to do in the event of a heat wave?
- Check traffic information regularly : on the Île-de-France Mobilités app, on your usual transport app or on the screens in stations and stations
- Hydrate yourself well during your journeys, drinking water fountains are available throughout the Region and in more than 140 stations and stations in Île-de-France
- Plan for a slightly longer journey time during heatwave alert periods and choose the best route from our calculator
- Visit the Île-de-France Mobilités app