[Talk-us] Prima Facie Speed Limits

Martijn van Exel m at rtijn.org
Tue Sep 9 21:09:58 UTC 2014

Thanks for clarifying, Tod. For ETA the congested urban use case is much
more challenging to get right, and much more likely to rely on an dynamic
ETA estimate. If you're on a multi-hour trip, you're more likely to have
scoped out your travel time before you leave and planned accordingly, and
if that estimate is off by perhaps 30 minutes, that's usually not the end
of the world. For many phone navigation apps, the commuting use case is
front and center, because the route people take to and from work will
depend a lot on live traffic conditions. (Remember Waze's slogan -
outsmarting traffic together, or something). So it's really navigation and
ETA going hand in hand to deliver the user the optimal way to work or home.

On Tue, Sep 9, 2014 at 3:00 PM, Tod Fitch <tod at fitchdesign.com> wrote:

> Yes, a "pretty small use case" at somewhere around 10,000,000 trips per
> year on I-5 through the central valley of California. Or 9,000,000 trips
> per year each way on I-8 across the desert to the Arizona border.
> On your daily commute, you may not need help navigating so much as you
> want accurate real time information about which routes are moving well
> compared to others. For me, trip planning and using a navigation device is
> not for local driving (I mostly use OsmAnd for local driving to help me
> find errors in OSM data) as much as for getting me to places I don't go on
> a daily basis. You could say it is a pretty small use case as most people
> don't drive to or through unfamiliar places everyday, but it is probably
> the biggest use case for a nav system there is.
> Cheers,
> Tod
> On Sep 9, 2014, at 1:17 PM, Martijn van Exel wrote:
> Agreed - that's a pretty small use case, relatively, though.
> On Tue, Sep 9, 2014 at 1:38 PM, Tod Fitch <tod at fitchdesign.com> wrote:
>> Historical and live speed profiles are pretty much required for trip
>> planning in congested urban areas, but for those of us who drive close to
>> the speed limit and make long trips on relatively uncrowded rural freeways,
>> travel time estimates based on posted (or prima facie) speeds are a good
>> approximation to reality. I travel between northern California and southern
>> Arizona a lot. The distance is about 1,300 kilometers and only a small
>> fraction of that is congested urban freeways (especially if I decide, as I
>> usually do, to avoid Los Angeles). OsmAnd with its knowledge of actual
>> posted speed limits (many entered by me) does a very good job at predicting
>> my arrival time.
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