Impossible Railways, Yesterday, 8pm
SINCE the 19th century, engineers have found ways to build railways through some very challenging environments, whether it’s mountains, wildernesses or even dense cities. This new series celebrates their achievements and looks at the design breakthroughs that made them possible. It begins by focusing on some of the planet’s most incredible metropolitan railways, from a unique inverted monorail in Wuppertal, Germany, to London’s ground-breaking Crossrail project and a little-known freight system in New York.

Inside No 9, BBC 2, 10pm
THIS week’s helping of dark drama from writers and stars Reece Shearsmith and Steve Pemberton centres on key protagonist Adrian, who spends his time photographing other couples’ weddings, but his own marriage to Harriet is far from happy. Can they renew their vows, spice up their love life and make a fresh start, or have they just run out of love, trust and time?

House of Saud: A Family at War, BBC 2, 9pm
EXAMINING how Saudi Arabia’s most revered family stays in power, featuring interviews with those who have worked for Saudi princes. They describe how the wealth allowed lives of privilege and pleasure out of the spotlight. But the growth of social media has meant Saudis are getting increasing insight into the behaviour of their rulers, including their transgressions. With this crucially important country facing a historic crossroads, the programme investigates what the future holds for Saudi Arabia and the rest of the world.

24 Hours in A&E, Channel 4, 9pm
THERE’S no shortage of drama in this ever-compelling series, and the latest offering will leave many watching through latticed fingers. Gary, 50, is brought in to St George’s Hospital by ambulance after a garage collapsed and fell on his legs. His wife Peta joins him, while Maggie, 83, comes in to A&E with suspected sepsis. She’s joined by her son and daughter, who also deal with the fact their mother has lung cancer. Plus, cameras follow one-year-old George, who is rushed in with his mother after drinking nail varnish remover.