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Home » Road Data » Speed Data

12/17/2009 3:16:35 PM

RobT
RobT
Posts: 62
Hi,

Has anyone used car speed data from Trafficmaster or ITIS in Accession? I would be keen to find out peoples experience of this. Also has there been any word on the TomTom dataset?

Rob
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12/18/2009 11:35:29 AM

Steve_L
Steve_L
Posts: 15
Hello
We use Strategis to analyse Trafficmaster data and I've been trying to import data from Strategis to Accession. I'm having problems with the fact that Strategis uses two-way links ie different speeds in each direction. Is it possible to assign a different speed to each direction of a link in accession?

regards

steve l
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10/12/2010 4:12:37 PM

eddiejames_uk
eddiejames_uk
Posts: 21
Hi,

I'm currently trying to get Traffic Master ave car speeds into Accession to replace the default speeds defined by the DfT by road classification.

Traffic Master data is appended to the network bi-directionally and there represented as two links i.e. a speed for each direction. I've not worked out how to assign these speeds as per the direction in Accession.

Have any of you guys managed this?

Edward.
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10/12/2010 4:47:44 PM

admin
admin
Administrator
Posts: 397
Accession can only recognise one speed per link, i know that some users have used different speeds dependant on the time of day and type of calculation. This could be a good suggestion for the feature request - bi-directional link speeds.



Regards,




Dan
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10/14/2010 4:07:21 PM

eddiejames_uk
eddiejames_uk
Posts: 21
Following on from my previous post RE using the Traffic Master data to replace the DfT default speeds in road based car calculations I’ve progressed my methodology as follows;

The first thing I did was calculate the weekday AM peak mean annual speeds (kph) for individual links (excluding public & school holidays) using the 08/09 Traffic Master data.

Accession does not allow bidirectional analysis so I calculated the minimum speed of each link. You could also use the average I guess.


The resultant table (link and speed fields) was imported into the Access file of the respective Accession repository.

The Access 'Road Link' table was updated using an update query on the 'CarSpeed' field.

In the above process links with no speed data are assigned a 0 value - not good if they occur on principle roads and will be treated as a road block. This is overcome by assigning an average speed to all CarSpeed fields that equal 0 - again by the means of an update query. Different speeds can also be applied to different link classifications.

The calculation was run through the road network for the car mode. NB origins residing adjacent to links with a speed of 0 will be reported as having no accessibility as they effectively snap to these and then cannot progress. It is therefore important that all links have a value, except those that cannot be driven down.

The results indicate the shortest travel time through a network for each O/D pair. NB it is important that the ITN network is used which indicates restrictions i.e. banned turns. If you import the road network as a map layer I found that this information is omitted.

I've found the results to be quite accurate and much better than using the default speeds by link classification provided by the DfT.

Let me know if you have any further questions, and let’s hope that future editions of Accession are able to consider bidirectional speeds and provide the facility for displaying the route/s taken.
It would also be useful if Accession would consider O/D pairs rather than routing to the nearest destination. Any thoughts?

Ed.
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