HOV "Lanes"

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Re: HOV "Lanes"

Postby AndyPoms » Mon Jul 29, 2013 11:16 am

The lane guidance in other GPS units is done essentially by segment - it doesn't actually know what lane you are in, but information about the number lanes on the segment you are on.

Besides at a 95% confidence level, civilian GPS is only accurate to 7.8 meters (just over 25 feet)(1) - and minimum lane width in the US is 12 feet (2) so 25 feet covers two full lanes on either side.
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Re: HOV "Lanes"

Postby jwriddle » Mon Jul 29, 2013 12:32 pm

AndyPoms wrote:The lane guidance in other GPS units is done essentially by segment - it doesn't actually know what lane you are in, but information about the number lanes on the segment you are on.

Besides at a 95% confidence level, civilian GPS is only accurate to 7.8 meters (just over 25 feet)(1) - and minimum lane width in the US is 12 feet (2) so 25 feet covers two full lanes on either side.


You're a walking Wiki of stats. :o


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Re: HOV

Postby AndyPoms » Mon Jul 29, 2013 1:45 pm

jwriddle wrote:
AndyPoms wrote:The lane guidance in other GPS units is done essentially by segment - it doesn't actually know what lane you are in, but information about the number lanes on the segment you are on.

Besides at a 95% confidence level, civilian GPS is only accurate to 7.8 meters (just over 25 feet)(1) - and minimum lane width in the US is 12 feet (2) so 25 feet covers two full lanes on either side.


You're a walking Wiki of stats. :o
I looked it all up & I cited my sources (the little numbers in parentheses).
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Re: HOV "Lanes"

Postby jwriddle » Mon Jul 29, 2013 1:54 pm

AndyPoms wrote:
jwriddle wrote:
AndyPoms wrote:The lane guidance in other GPS units is done essentially by segment - it doesn't actually know what lane you are in, but information about the number lanes on the segment you are on.

Besides at a 95% confidence level, civilian GPS is only accurate to 7.8 meters (just over 25 feet)(1) - and minimum lane width in the US is 12 feet (2) so 25 feet covers two full lanes on either side.


You're a walking Wiki of stats. :o
I looked it all up & I cited my sources (the little numbers in parentheses).


Now you're just showing off. ;)


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Re: HOV "Lanes"

Postby russblau » Mon Jul 29, 2013 3:22 pm

I'm sure AndyPoms is right, but even without any stats, all you have to do is look at the GPS layer in the WME and you can see how wildly inaccurate some GPS readings are. If memory serves me right, I believe it takes 20-30 minutes of continuous operations for a GPS unit to reach full accuracy, too, so we are unlikely ever to approach "lane-level" accuracy for users with relatively short commutes.
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Re: HOV "Lanes"

Postby CBenson » Mon Jul 29, 2013 3:55 pm

But given enough data, you don't have to every car plotted in the correct lane to extract some speed difference data from the lanes. I suppose volume discrepancies could overwhelm speed discrepancies. But I would not take the inability of consumer GPS receivers to place a car within a lane width to mean that plotting HOV lanes would be useless. Furthermore, if there is a significant speed difference say between 55-65 mph in the HOV lane and 35-45 in the regular lanes, then we can likely assume that clients that have self identified as HOV are in the HOV lanes. Thus, I continue to think that once a user can self identify as an HOV vehicle, then this topic should be revisited.
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Re: HOV "Lanes"

Postby jemay » Mon Jul 29, 2013 4:06 pm

jemay wrote:The HOV wiki entry
...
I bring this up to help with the wiki understanding of what needs to be mapped for HOV lanes. The HOV wiki page should state that no HOV lanes should be mapped if it is a "free will" lane.


Wiki Page wrote:As an interim measure, these lanes should be added to the map as separate roads, with the road type as Parking Lot Roads. This means that if you are not currently in one of these lanes the routing will avoid it, but if you choose to get into the lane, the routing will work correctly.

I think something like this needs to be added.

... will work correctly. This should only be applied to dedicated lanes that have exit and entry points.
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Re: HOV "Lanes"

Postby JimB50 » Tue Jul 30, 2013 3:16 am

Andy is right!!

@Russblau: the high end accuracy is obtained after 20-30 minutes that the GPS is motionless and only for that specific location. Once the GPS is in motion the accuracy drops dramatically.

The accuracy depends on the combination of the quality of the antenna and the radio. It comes down to how many satellites can be received simultaneously, the processor speed and how long the system stays motionless. Not exactly the best concept for a GPS app using a smartphone GPS. :o

That said, if Waze can keep track of who is on the HOV/HOT lane then it should be relatively straightforward, maybe not easy.

In response to CBenson's comments, another place where there are speed differences is at stop lights where the wait time is dependent on the direction taken after the light. It becomes even more fun when this intersection is at a freeway exit. Then there can be a multitude of potential directions. With different signal timing and right turn on red.

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Re: HOV "Lanes"

Postby bgodette » Tue Jul 30, 2013 4:30 am

Non separated HOV/HOT lanes should remain unmapped and left until we get some of the additional attributes from Google. This will include number of lanes and hopefully you can specify how many lanes are HOV/HOT. That combined with car profile in the client can separate out average speed data between HOV/HOT and regular lanes.

Or we wait 5 years for all our phones to have GPS chips that use the three (four?) major GPS systems at the same time for sub 1 meter accuracy. :ugeek:
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Re: HOV "Lanes"

Postby Daknife » Tue Jul 30, 2013 5:37 am

AndyPoms wrote:The lane guidance in other GPS units is done essentially by segment - it doesn't actually know what lane you are in, but information about the number lanes on the segment you are on.

Besides at a 95% confidence level, civilian GPS is only accurate to 7.8 meters (just over 25 feet)(1) - and minimum lane width in the US is 12 feet (2) so 25 feet covers two full lanes on either side.

Not entirely true, more devices available today are compliant with the WAAS system for which the above cited stats are the set minimum requirements to be considered compliant with the WAAS specification, but in testing by the NTSB it has proven to consistently provide an accuracy of 1m (3ft, 3 in) or less laterally, accurate enough even for GPS based flights and landings. Many older handset GPS's are not WAAS standard but more and more of the newer ones are are, and external receivers such as the Dual150 Bluetooth receiver are WAAS compliant. This standard is considered sufficiently accurate for aviation uses, as that was the primary reason for the creation of the WAAS system. And since Selective Availability was turned off by the DOD in 2000, even Just plain vanilla GPS measures to greater accuracy than the 7.8 meter minimum requirement for WAAS. Vanilla GPS measures at an accuracy of 2.5 meters. http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
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