Car Tech

Who Writes Highway Sign Messages? And How?

You’re on the highway, and you notice the overhead sign: TRAFFIC MOVING SLOWLY AFTER NEXT EXIT. But everything around you is moving smoothly, so how do they know what’s up ahead? And what should you do when you see such a warning?

As far as figuring out the slowdowns, you might think it’s just someone looking out a window or at a camera feed somewhere, and keying in the information. Camera monitoring is part of traffic information, but there’s even more high-tech wizardry as well.

According to Ontario’s Ministry of Transportation, “travel time information posted on selected variable-message signs during the peak periods are automatically monitored and updated by Bluetooth sensors deployed at key locations along the urban freeway network.”

What the sensors are monitoring is the Bluetooth that’s included in virtually every newer car today. They pick up each vehicle system’s unique MAC (media access control) identifier address, and match it as the vehicle drives between the sensors that are set up along that stretch of road. After an algorithm eliminates matches “that are considered outliers,” perhaps such as a vehicle slowly merging back into traffic from the shoulder, the system determines how long it takes vehicles to pass by the sensors, and uses that to calculate their speed. It then adjusts the sign to indicate if traffic is moving at a normal clip, or if there’s a jam ahead.

If the selected route has separate express and collector lanes, the system will monitor both, and then use the signs to inform drivers how each set of lanes is moving.

Where does all this data go?

The system doesn’t identify vehicles to specifically track them individually – at least, we’re assuming it doesn’t, keeping our tinfoil hats handy nevertheless – but instead compiles information from the MAC addresses of each vehicle and then considers all the vehicles as a group. It’s a common scenario among companies that provide traffic information. Applications such as Google Maps monitor the location services provided by phones. The system then analyzes how many people are on a specific road and how fast they’re moving, and sends a warning if enough slow-moving phone users indicate a traffic tie-up.

Many overhead warning signs – and your phone map apps – may also factor in variables such as road construction (the map companies stay updated with information from local municipalities); notifications from police about crashes or other activity; or the usual traffic patterns, such as bottlenecks expected every rush hour.

And it isn’t just real-time applications that use such information. Harold Goddijn, CEO of navigation company TomTom, says his company monitors vehicles using the GPS integral to the navigation system. It’s impossible to continually send out employees to drive every road to look for changes, so as with the highway sign system, the company compiles the tracking information to monitor traffic flow. “If we see a lot of people driving on what we think isn’t a road, we look at satellite pictures to see if there’s a (new) road there,” Goddijn says. Likewise, if large numbers of drivers are going the wrong way on a one-way street, the company checks to see if the municipality has altered the direction.

What’s next?

And all of this is paving the way for systems that will eventually monitor and track individual vehicles, which will be essential if we’re ever going to have cars without steering wheels. Several automakers currently sell cars that can drive themselves under limited circumstances, but they’re strictly reactive: they brake when the vehicle ahead does, and they follow the lines on the road. They can only work if exactly the right conditions are present.

Truly autonomous cars must be proactive, knowing where to turn, where to park, and what to do if they’re faced with something unexpected. This is where we’ll need vehicle-to-vehicle (V2V) communications where cars “talk” to each other, such as warning others when they’re coming up to intersections, or telling vehicles behind them that they’re aware of a collision up ahead. We’ll also need vehicle-to-infrastructure (V2I), a much wider-range and consequently more expensive proposition where beacons broadcast information to vehicles in the vicinity – there’s a parking space here, the traffic light is red, there’s a pedestrian entering the crosswalk.

But for now, we have this far simpler (yet still complex, when you think about it) system of monitoring vehicles as they pass by, in order to give you the latest on what you can expect up ahead. The information is there – use it!

So when you’re on the road…

If the sign warns that traffic is moving slowly after the next exit, consider your options. If you know the surrounding roads well enough, or have a GPS device to show you, you can hit the streets to go around the highway clog. Of course, it’s always a crapshoot, because by the time you make your way to a street that’s parallel to the highway, wait for lights, wait for pedestrians and traffic, make all your left-hand turns, and then travel back to the next highway entrance, it could take longer than if you’d just dealt with some of the bumper-to-bumper stuff (providing the highway is just slow, rather than completely stopped for a major collision, or that the jam doesn’t persist for several exits).

If you’re planning to stick with your original highway route, start slowing down. Even if traffic is still moving, adjust your throttle to scrub off 5 to 10 km/h. Look as far ahead as you can – which you should be doing at all times anyway – and as soon as you first see the wall of brake lights, slow down some more. The idea is that you, and the vehicles behind you, decelerate gradually as you approach the jam. It’s very dangerous to stay at top speed and then suddenly brake hard when you reach the slow section.

Always assume that other drivers have not bothered to look at the overhead sign (it’s amazing how many don’t). If there’s a considerable gap between you and the vehicle behind you, turn on your four-way flashers as you slow down, to warn that driver that you’re dropping your speed.

If an overhead sign gives you additional information, take advantage of it. If it tells you that the express lanes are slow but the collectors are moving, exit onto those lanes. (And again, note how many people don’t, and simply drive up to the traffic jam – really, folks, read these signs!)

If the sign warns you that your lane is closed ahead, then start looking for an opportunity to move into an open one. Yes, the zipper arrangement really does work – when vehicles fill both lanes to a closure, and then take turns getting into the through lane – but only if everyone involved actually does the zipper merge properly, which seldom happens. And if there’s a warning of construction ahead, slow down. Road construction workers can be vulnerable even if there’s a barrier in place. And finally, if the problem is a crash, look where you’re going, not at the issue. Rubbernecking not only slows down traffic, but it can lead to more collisions. The last thing you want is to be the one responsible for the SLOW TRAFFIC AHEAD message on the sign.