Those online or GPS-based maps that show all the freeways in your area, color coded (red, yellow, green) to show how traffic is moving…I am just in awe. What a marvelous invention! What an age we live in!
How does it happen? First, where are the sensors that pick up traffic speed, and how do they work? And then, how does the data get uploaded (and to where)?
(and then when you combine this with the other Marvel of the Age – GPS – I can just push a button in my car and see what my commute is going to look like. This is really amazing stuff.)
From Wikipedia, "Data is typically collected via loop sensors embedded in the roadways, then processed by computer at a central facility and distributed as a map view to users."
Doesn’t answer all your questions, but it’s a start.
I think it’s going to depend on who’s providing the data. I don’t know this for a fact, but I seem to recall reading somewhere that for example, in Google Maps, they get traffic data from actual google users who happen to be using google GPS navigation on that particular road. So google knows exactly how quickly people are moving along over there.
In my experience, the traffic info from standalone GPS units that retrieve their data via radio frequencies aren’t worth a soggy hot dog bun.
The last time I was stopped in traffic on the freeway I looked down and saw the detector loop sensors circles in the pavement. Had never had a reason to notice them there before.
All the other replies make sense. However, a similar question I’ve had, is why can’t the GPS systems in everyone’s car be utilized to get real-time congestion reports? Like…a map that says “There’s 350 receivers per X distance on this road” and that might translate to heavy traffic, or light traffic. That would really give accurate and up to the minute traffic reports. I’m guessing people would get ornery and start thinking they’re being tracked by the gubmint. But really…GPS units aren’t registered to anyone in particular anyway.
I hope that this isn’t a hijack, since it’s a question that totally relates to the OP and might even be answered in a way to provide answers the OP was looking for.
That’s only part of the answer. There are only loop sensors on the major highways. A much more modern technique that can collect traffic information on just about all streets is called using traffic probes or floating car data.
This is how Google, for example, can show traffic congestion even down to the bigger streets in residential neighborhoods.
Basically, if you’re driving your car and you have a cellphone turned on, you’re providing traffic information.
Or maybe just walking with a cellphone. Sometimes Google maps shows traffic on the pond-front road (that I can see outside my window) with the red and black “traffic is bumper-to-bumper” color. I wonder what’s going on, peek outside, and there’s no cars, just the the usual citizens taking their daily walk around the pond. It’s not consistent, though, so I wonder if it happens when a particular brand of phone or a particular carrier reaches critical mass.
The Milwaukee freeway system has these scattered around that I always assumed were monitoring the congestion. Of course, now that I think about it, I guess I tend to see them on ramps, but I don’t really pay close attention to them. If that’s not what they’re for, I’m still curious and keep meaning to start a thread about it anyways.
Actually, some GPS systems do contain transmitters, precisely for the purpose of transmitting traffic data to other GPS systems. It’s part of the floating car data network I mentioned above.
There is a LOT of work going into making route calculation more and more accurate, taking into account real time conditions. The goal is to get both the best routes and the most accurate arrival times. I’m in the industry (though I prefer not to say for what company) and I am aware that there are systems that consider current traffic conditions and make predictions about when you will arrive at your destination that are accurate to within a few seconds.
I think those loop detectors on highways are to provide estimated travel times that end up on a sign - those things that relay how far to specific spots, and how long it’ll take to get there.
Things like google traffic and what-not typically use crowdsourcing. Not sure of the exact algorithm, but I’d think that if they sense 150 cell phones in a small area of only 75’ of a multilane highway, they know traffic isn’t moving fast.
