Summer is well and truly here and Melbourne has been one of the main targets for heatwaves in recent weeks. While we know it can be a catalyst for catastrophic bushfires and cause all sorts of health problems, heat can also cause a public transport meltdown with interruptions to your daily commute. The blaring sun causes train tracks to expand, causing cancellations and delays. A Metro spokeswoman said rail temperatures were being monitored and they were bracing for more extreme conditions later today, which may cause trains to move slower. Each train line is fitted with electronic monitoring sensors that measure the track temperature. "We are able to apply speed restrictions to the affected parts of the network only," the spokeswoman said. "Speed restrictions will be introduced on individual lines if the track temperature exceeds 55Â°C. "When the track temperature reaches 55Â°C, the maximum speed limit of that line is restricted to a maximum of 80km/h." As part of Metro's extreme heat strategy, maximum speed limits are reduced to 70km/h across the entire train network once the weather hits 42Â°C or above, causing delays as the train can usually travel about 110km/h. The Bureau of Meteorology has forecasted a top of 41Â°C for Melbourne today. Unlike Metro, V/Line has been forced to cancel some of its train services but has replaced them with buses. The 3.17pm train from Southern Cross Station to Wendouree has been replaced with a coach due to heat and speed restrictions. The heat has also caused the train from Southern Cross to Eaglehawk to be cancelled and replaced with a bus. V/Line tracks begin expanding when the temperature hits 36Â°C so the transport service needs to take more drastic measures during the state's heatwaves. Trains on the Geelong line have also been impacted, and those planning to catch the 5.55pm from Southern Cross Station to Marshall will instead have to ride in a bus. Services at 5.33pm and 5.44pm from Southern Cross Station to Waurn Ponds will also operate as a bus. Coaches will replace trains on the Gippsland line this afternoon and delays are expected on the Seymour line. Customers have been advised to allow extra travel time for their journey and V/Line staff will be handing out bottles of water to customers travelling this afternoon. Across the network, V/Line had 14 days of heat speed restrictions last month compared with three days of restrictions in December 2014. "We thank customers for their patience and understanding during the summer months and will be doing everything possible to minimise disruptions," a V/Line spokeswoman said With scorching temperatures, people are also reminded again not to leave children in parked cars. In December alone, Ambulance Victoria was called to 225 cases of parents leaving their children in the sweltering conditions. There were 64 more children left in cars in December 2015 than in 2014. On just a typical summer day, a parked car can be 20 to 30Â°C hotter than outside and a child's body temperature rises three to five times faster than an adults. Leaving your child in a car in Victoria can cost you almost $3,700 in fines and you could face up to six months in jail.