Vehicle platooning is part of a suite of features that self-driving cars might employ. A platoon is a group of vehicles that can travel very closely together, safely at high speed.
Each vehicle communicates with the other vehicles in the platoon. There is a lead vehicle that controls the speed and direction, and all following vehicles (which have precisely matched braking and acceleration) respond to the lead vehicle’s movement.
Original ideas for vehicle platoons involved some kind of mechanical coupling, like you’d get in a train. Modern communication such as Bluetooth and wireless, GPS, radar-sensing systems plus drive-by-wire steering and throttle allows for computers to take control of cars.
Potential upsides of vehicle platooning
- It improves the aerodynamic effectiveness and performance, increases the capacity of roads and provides a more steady state traffic flow.
- Because the vehicles are ‘drafting’ one another, it reduces fuel consumption, and with all the cars travelling close together and moving at the same time, efficiencies can be gained when vehicles move away from traffic lights, for example. With human drivers, each driver waits to see the vehicle in front move, then moves away, leading to a reverse concertina effect.
- Initially each vehicle in the platoon would have a driver at all times, but eventually driverless (self-driving or autonomous) vehicles will be able to automatically join platoons that may function like long trains of vehicles on a highway, and drivers would be free to enjoy the benefits of having a driverless vehicle, such as being able to watch a movie or do work.
- It could possibly reduce accidents (although, this is likely to happen over time anyway due to emergency braking systems that are being included in new vehicles now)
Potential downsides of vehicle platooning
- Long platoons may prevent other vehicles from changing lanes when they need to unless they are aware of other drivers’ intentions, for example, monitoring a turn signal/indicator.
- A platoon will require a cultural shift away from being in control of a motor vehicle to giving complete control and travelling very closely.
- No computer system is 100% secure and platoons could be hacked (one reason why a driver should be present in each vehicle). This logic also applies to autonomous cars, too.
- Vehicle platoons in towns may not work in heavy traffic as a lead car might cross a junction but there might not be enough room on the other side of the junction to accommodate all other cars in the platoon, thus the junction will be blocked.
- Vehicle platoons cannot work at stop signs because they would contravene the road code, which states every vehicle must stop and check to see if it’s safe to go.
- Drivers will need to learn new skills.
- Platoon functionality may be difficult to retrofit to existing cars.
- The technology will increase the cost of new cars.
- Insurance companies may not accept the liability for accidents caused by platoons of vehicles.
- If the lead vehicle does not have time to react to an obstruction, e.g. a vehicle turning in front of it leaves it no room to stop, all other vehicles will most likely be involved in the crash due to the proximity of driving. I.e. in normal driving, drivers would (theoretically) obey the two-second rule, giving them much longer to stop. Human drivers may also be able to alter course and react given a broader field of view than vehicles travelling in close proximity.
- Drivers need to be able to leave the platoon at any time and reform into other platoons, or take control completely. This is because not every car’s final destination will be the same.
- Some drivers may attempt to drive in a platoon without having the requisite technology or skills.
- Driving in a platoon will normalise people’s expectations of travelling very close to the vehicle in front and could lead to more tailgating.
Solving the downsides
These systems have been proposed since the 1960s and various work at universities around the world has resulted in different systems.
Some of the downsides can be solved using an automated highway system (AHS). This is a dedicated lane for platooning cars. Cars will travel in platoons of up to 25 vehicles using embedded sensors in the road. The vehicles would maintain a distance between one another of around one metre to maximise aerodynamic efficiency.
The AHS can have embedded information in the road way to give vehicles clues about what speed to travel. However, modern radar and camera technology is now good enough for vehicles to interpret data in 3D and combine this with traffic reports to determine an appropriate speed. It’s also extremely expensive to dig up the roads to add this technology, or to create new roads with the technology.
Volvo has also demonstrated platooning on normal roads with three cars driven autonomously behind a lead truck driven at speeds up to 90kph with a gap of no more than 6m. This system is called SARTRE (Safer Road Trains for the Environment).
Vehicle platooning is practical only on motorways, and only in the right-hand overtaking lane. In New Zealand, that doesn’t give much opportunity for benefits like it would in Europe or America.
You can read our article on self-driving (autonomous) cars here (opens in a new window).