The humble circular intersection was first introduced in America in 1907, England and France followed a couple of years later and made them important parts of their current travel infrastructure. They now host over 10,000 and 30,000 roundabouts respectively, while the US has around 3,000. Roundabouts pose a particular challenge to self-driving cars as no two are the same; some have more than one lane and cover large areas, others are simply a tiny white circle in the middle of a country road. It's Nissan's job to detect their various forms and treat them all in the same manner.
When we approached the first roundabouts, the Leaf was cautious but navigated them with ease. In fact, the first third of the journey was largely uneventful, mainly owing to the fact that the ExCel and the surrounding area aren't especially busy at 2:30pm on a Wednesday afternoon.
That calm, however, was soon punctuated by an accident. Not one involving us, but a collision between a car and an Ocado delivery van on a slip road joining the A13. It gave me the perfect opportunity to see exactly how a machine deals with an unexpected event between vehicles of differing sizes on a fast-moving filter road.
Approaching the incident, the Leaf recognised that the van and the car were stationary on the right side of the two-lane slip road and kept left in order to pass the obstruction. The radar soon picked up other cars attempting to merge in front of us and the software intelligently gave way. It didn't take very long to clear the accident, but it was clear that Nissan's current programming is designed to be overly cautious. A human driver might not have been so accommodating.
There were no causes for concern on the 50mph A13. The car piloted itself without incident and then exited the carriageway to tackle the final residential stretch of Prince Regent Lane. Here, the street's varying road markings, parked cars and an abundance of pedestrians provide a different challenge.
Bus stops, traffic bollards and zebra crossings weren't enough to phase the Leaf, but two young men crossing the road were enough to make it pause for thought. The duo were a couple of metres ahead of the Leaf and were heading towards the convenience store on the other side of the road. They had barely stepped off the pavement, on the side that was opposite our lane. The Leaf was moving at such a lick that they posed no threat -- by the time they reached our side of the road, we would have been long gone.
It immediately made me ponder what a human would do in that situation. In my experience, a human driver would have acknowledged their presence and identified that they didn't pose a safety issue because there was a significant distance between them and the car. Also, the chevrons in the middle of the road would have provided a natural place for them to pause during their crossing. I posed this question to Iijima-san and he simply said: "This is one of the reasons we are testing in Britain."
Questions that need answers
We returned to base without incident, allowing me to reflect on what I had learned from my brief trip in the Leaf. In April 2016, I tested Tesla's semi-autonomous Autopilot feature in the Tesla Model S and it's impressive to see just how far these technologies have developed in under a year. Nissan's Leaf is already demonstrating a basic mastery of English roads, but its executives admit that its system is prone to mistakes, as a reporter from The Guardian found out. It is a prototype after all.
By 2020, Nissan wants its cars to have mastered single and multi-lane carriageways and intersections before it can deploy its fully autonomous platform ready for the Tokyo Olympics. The company will start by integrating single-lane autonomy into the Leaf and the Qashqai, its two most popular vehicles, later this year. It will then expand the full autonomous ProPilot system to eight more models over the next three years.
To get to this stage, Nissan will need outside help. First, governments around the world need to specify new rules of the road for self-driving car makers. Then, it'll need to direct insurance companies so they are able to cover drivers and the autonomous systems inside their vehicles. The hardest task it faces, however, is convincing the public that their systems are safe and necessary additions to the future cars they will buy.