About a century ago, an Act of Parliament approved the system of 70 driverless trains as a way of delivering mail to different points throughout the city. In its prime, the system carried 12 million items a day. That's amazing in itself -- truly the peak of paper mail -- and the rational upon which it was built adds even more color.
The BBC writes that "a report looking at the case for building the railway concluded London's traffic speeds would never surpass 6mph, convincing MPs to approve plans to build the railway, which could run at 40mph."
That prediction obviously turned out to be incredibly wrong, however the system still ran through the end of the 20th century, closing in 2003 when it was finally deemed too expensive to operate.
We'll keep on an eye on any news regarding its future. For now, go ahead and peruse the photos. If the tunnel begins to look familiar, it might be because you've seen it before as the set for Bruce Willis' film, Hudson Hawk.