a signage mystery

[cellio]

I-376, like many other highways, has those overhead digital signs that somebody updates with topical messages like "accident, right lane closed 1 mi" or "stadium parking exit 72A" or, when they've got nothing better to say, "buckle up -- it's the law". There are two of these signs on my commute that, in their default states, say "distance to downtown: N mi, M min". Which, while usually not especially helpful to me (I live five miles from downtown), is still more useful to me than seatbelt nags. (I always use seatbelts.)

This morning, while stopped in traffic near Oakland, I saw one of those signs update from "4 mi, 5 min" to "4 mi, 6 min". That was less inaccurate, but far from accurate -- I reached downtown about 25 minutes later. (This is all very unusual; two of three lanes were closed due to a bad accident. My commute is sometimes slow, but I don't remember the last time I was in stopped morning traffic.)

It got me wondering -- do the indicators on those signs update automatically based on sensor data or are they human-controlled? The fact that an update happened but didn't jump to a more-appropriate number makes me think that we're dealing with an automated system that only bumps one unit at a time. (I would hope that a human would have updated it to warn about the accident.)

Why would it be designed to only increment in single units? Or is it a bug? What are the inputs to these signs, anyway?

Comments

[cellio]

Oh, bluetooth. Does this assume that the phone's bluetooth is on (because the person is using an earpiece) and it connects automatically? Or is there some reason for a driver to intentionally connect to the car's bluetooth? (I never use bluetooth unless there's a specific reason, like casting to my TV, so it hadn't occurred to me.)

This seems like the sort of application that would be pushed by insurance companies and law enforcement, not something drivers would voluntarily choose.

GPS can't help except by noting that the phone is moving at a speed consistent with a vehicle, faster than a pedestrian.

It needs the speed information, but GPS plus other phones' GPS, and GPS plus map data, seems relevant?

[dsrtao]

It assumes that BT is on because most people leave it on all the time. It assumes that the car has a BT interface because new cars do.

People use BT in their cars primarily for listening to music from the phone over the car's audio system, and secondarily for using the car's audio system for phone calls.

GPS plus other phones' GPS, and GPS plus map data, seems relevant?

Only if you are Big Brother tracking all the phones over an internet connection. Remember, GPS is a one-way radio signal from satellits not dependent on the Internet; any time you think "GPS tracker" you are thinking about an integrated system with map data, mobile data connections and active processing.

E.g. you could build something like that, and GPS would be part of the solution, but you can't do it all on a single phone no matter how smart it is. The phone knows how fast it is moving by knowing the time and a series of position updates; it might or might not have an accelerometer and a compass. It doesn't talk to other random phones in the area to find out if they are moving at the same speed, and if it did, every car in a traffic jam would be difficult to distinguish from the others...

[cellio]

Oh right; I made the jump from "Google (e.g. maps) has all the data" to "an app has the data". An app that did this would only be useful if lots of people were running it, which presumably they'd only do if the government required it or insurance companies incentivized it.

(State Farm just offered me a whopping 5% discount if I'd install and run their app. Er, no. A price might exist (it did, it turns out, for health insurance -- share this data to avoid a surcharge), but if so it's a lot higher than 5% of my modest auto-insurance bill.)