One of the benefits of fully autonomous vehicles, we are told, is their ability to do away with so-called “phantom traffic-jams” — those traffic tie ups that happen for no concrete reason. Ford and Vanderbilt University set out to explain the phenomenon and how autonomy will solve it.
“Unlike the traffic jams caused by accidents or road construction, phantom traffic jams appear out of nowhere,” said Daniel Work, civil engineering professor at Vanderbilt University. “Combined, traffic backups cost the typical American commuter on average an additional 41 hours a year sitting in traffic at a cost of $1,400 per commuter.” (Taking into account lost productivity, fuel burned while idling and increased wear and tear.)
A variety of factors outside of crashes and construction zones contribute to traffic bunching up — poor merging practices, slow driver reactions, overly aggressive or unnecessary braking, and just poor driving habits in general.
“A fun family road trip can quickly become irritating when traffic slows to a crawl – especially once you learn there was no reason for the gridlock,” said Michael Kane, supervisor, Ford Co-Pilot360 Technology. “We encourage Ford owners who have adaptive cruise control to use it during their summer travels in the hope this smart technology today can be that first step to help ease commutes.”
A team of researchers recently took to a closed Ford test-track to demonstrate what happens when as few as 36 cars get bunched up due to drivers physically braking and accelerating according to their personal comfort zones, and how the road dynamics change when adaptive cruise control (ACC) handles those driving tasks.
The demonstration on a high-speed oval had 12 rows of cars across three lanes of traffic following each other at 60 mph (96.56 km/h), the front row of cars suddenly slowed to 40 mph (64.37 km/h). The following cars all reacted in various manners to the braking ahead of them and within three rows, there was a discernible bottleneck starting, with some of the cars in the final rows coming to an almost complete standstill.
When the same experiment was performed with adaptive cruise, with the lead cars performing the same manoeuvres while the cars behind them had their adaptive cruise control set at 100 km/h, the bottleneck effect completely vanished, with the measured speed of a car in the final row decreasing by just 8 km/h.
“For years, traffic researchers and engineers have been looking to smart vehicle technologies to reduce traffic congestion, whether that’s vehicles that talk to each other or vehicles that can predict the road ahead,” said Vanderbilt’s Work. “This demonstration was a unique opportunity to understand how commercially-available active driver-assist technologies can be used to positively influence traffic flow.
“The fact that we saw a commercially-viable ACC system fully suppress the traffic backup is quite impressive,” he added. “And while we know this won’t happen in every situation or in every circumstance, it’s very promising to see that commercially available ACC systems can already have a desired effect in normal, everyday driving scenarios.”
But of further interest, was the discovery that when the number of ACC active vehicles was reduced to 33% (one in three cars with ACC), which is the base threshold researchers have long believed could deal effectively with phantom traffic-jams, the gridlock-busting benefits were still realized.
“Adaptive cruise control systems don’t get tired or distracted, they’re consistently looking at the vehicle ahead,” said Ford’s Kane. “Plus, they are programmed to provide more consistent distances between vehicles, so they can better respond to the speed and distance of the vehicle ahead.”
But Work cautioned that most ACC systems can’t see beyond the vehicle ahead, so the system is always reacting to what is happening directly in front, whereas human drivers have the ability to watch traffic two and three vehicles ahead and are better able to tailor an appropriate response to an approaching slow-down.
Work and lead PhD researcher Raphael Stern plan on publishing the results of the Ford demonstration in an upcoming academic journal.