Computing Arrival Times

 

My sneaking suspicion is "arrival time" never factors in stoplights or stop signs. Assuming traffic is moving at or around the posted speed limit, I find the time is fairly accurate for interstate driving, but never accurate for surface streets.

Is the arrival time computed by only factoring in remaining distance to be traveled and the speed limit on those roads, or is there a traffic light/stop sign slowdown factored in?

-Tom

My Opinion

GPS devices don't know speed limits. They do know distance and calculate an approximation of travel time based on that distance (and speed travelled from start to destination). As the route is travelled, they constantly compute time and distance travelled (as well as the speed you have driven), and remaining distance to be travelled, and update the arrival time. If you sit still at a red light for 3 minutes, your arrival time is automatically updated by the 3 minutes. As you approach your destination, it gets down to an "exact science" within the device so that you arrive at exactly the time it calculates. It makes it look like a genius, while in reality, it's a simple process for a computing device.

Joel

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"Sometimes, when I look at my children, I wish I had remained a virgin". Lillian Carter (Mother of Jimmy Carter)

PaintballCFO wrote "GPS

PaintballCFO wrote "GPS devices don't know speed limits".

I don't believe that to be a true statement. I did a simulation of a drive between home and northern minnesota for an uncoming trip and it does tell you that your speed is simulated at 32mph for secondary streets and 62mph for highways. Just my observation. Maybe someone else who is more familiar with the technology can chime in.

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******************Garmin Nüvi 1300T****************Member 6523*******************

re: arrival time

[quote=krmidas
Is the arrival time computed by only factoring in remaining distance to be traveled and the speed limit on those roads, or is there a traffic light/stop sign slowdown factored in?

I am sure the systems don't take into consideration traffic lights and stop signs. I believe they have several speeds for types of roads.
See previous discussion on this topic: http://www.poi-factory.com/node/714

I know my experience on highways with 70mph limits is that if I travel at early morning or late evening hours with no traffic, even though I am travelling 75-80, I still arrive at the original estimated time on a 1/2 hour trip.

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Garmin StreetPilot c530, Mapsource

2720 does a very good job

My 2720 is generally very accurate with its estimated arrival time. It has different speed limits for different classes of roads, city vs rural. It uses those speed limits in its calculations when trying to find the fastest route - in part, that is why it generally favors Interstates - they have a higher avg speed. The only time the arrival time is not very accurate is when I have peak travel problems - the GPS cannot very well know much about travel patterns during peak commuting hours.

In summary, I'm very impressed with the accuracy of its estimates for arrival times.

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___________________ Garmin 2455, 855, Oregon 550t

The GPS may not know speed limits...

PaintballCFO wrote:

GPS devices don't know speed limits.

The GPS may not know speed limits, but it knows if you are travelling on a surface street or an interstate, since it can alter your route based on preferences for time vs. distance, and can avoid interstates if you choose to. Therefore it should be able to compute your arrival time based on a combination of remaining distance/average speed/route. It would seem simple enough to just slow the average surface street speed by 15% to compensate for stoplights.

-Tom

Did you ever notice?

mkahn wrote:

[quote=krmidas
Is the arrival time computed by only factoring in remaining distance to be traveled and the speed limit on those roads, or is there a traffic light/stop sign slowdown factored in?

Quote:

I am sure the systems don't take into consideration traffic lights and stop signs. I believe they have several speeds for types of roads.
See previous discussion on this topic: http://www.poi-factory.com/node/714

Quote:

I know my experience on highways with 70mph limits is that if I travel at early morning or late evening hours with no traffic, even though I am travelling 75-80, I still arrive at the original estimated time on a 1/2 hour trip.

I'm a truck driver, and usually you can guestimate your arrival time based upon 50 mph, combining highways and county roads, with ramps, stop lights, slight traffic, etc. Just as an experiment, check your overrall "traveling" speed on your GPSr's. Back in the day, we never even used speedometers, just tach's to guage shifting, and knew that 300 miles would take us 6 hours...still holds true, even with greater (65 mph) highways.
Dan

I'm with the trucker

I still do the mental calc's in the noggin using 50mph, and yes, it's still pretty close.

Now, with the new gizmos - who really cares how it's calculated, it's still time and distance.
Ya get in, turn it on, pick your destination, and it tells ya when you are gonna get there. If you encounter a delay enroute, it updates your arrival time. If you can manage to carry on for a pretty good stretch, it updates your arrival time....

I'm still stickin with the trucker smile

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........Garmin StreetPilot c550 / Nüvi 765...........

I asked a Garmin support

I asked a Garmin support tech whether there was a way to speed up the "simulated trip." He said, "No, it just runs at the speed limit of the route."

Now, whether he meant the actual speed limit or just an estimate based on road type, I don't know. But I don't see any reason that speed limits could not be included in the map data.

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Nuvi 55LMT

garmin support also to me

garmin support also to me that but adj for ur actual speed.

See screenshot