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Isn't this solved by GPS and maps with speed limit data? Google maps gives me nonsense speed limits in a couple of places but mostly correct.
by incone123 4y ago
Isn't this solved by GPS and maps with speed limit data? Google maps gives me nonsense speed limits in a couple of places but mostly correct.
- samatman 4y agoNo, because the lower speed limits posted on flashing signs for construction are an important local case. In my experience, Google just thinks those are traffic jams. I've seen Maps 'know' about road construction speed limits, but it isn't usual.
- incone123 4y agoGood point. Also, M25 (London orbital motorway) has large sections with variable speed limit. Google maps navigation just doesn't show a limit for those areas, since it does not have timely data.
- adhesive_wombat 4y agoAlso the 20mph boroughs really confuse the systems (cars and satnav), since they very often say 30 in 20 and also 20 in a 30. The various limits are, admittedly, not well signed, and I suspect that's deliberate to keep drivers cautious.
- labcomputer 4y agoOne problem is "map matching". That is, given your lat/lng (or, more realistically, a time-series of lat/lngs) and a map, figure out which road you're on. The thing is that most consumer devices with GPS (like phones and even standalone GPS navigators) have a lot of internal "magic" to hide the raw noise in location fixes from the GPS signal. For example, certain Garmin devices (intended to be used off road) will snap your location to an Interstate if you are going more than 55 mph and heading roughly in the direction of the road (which is evident when you run into traffic and your location keeps switching between the frontage road and expressway--the error distribution of the noise doesn't have mean=0!).