[OSGeo Africa] Travel Time Calculation

Tue Jan 15 20:02:34 PST 2013

Hi Uazu,

There is a quick/easy way to do what you require, if you do not have a specialist Transportation GIS System such as  TransCAD GIS, Or you do not want to get involved in routing.

What you require is:

1.       A road network that has a field that indicates the length of  each road link (from node to node)

2.       A field that indicates the posted road speed (this is the most easily available to source)

I am going to ramble on here a bit but just bear with me – presume that the road links are in km and speed is km/h. 

I Presume that you also do not have a morning peak hour/off peak hour and evening peak hour journey time for each road link.

I also have no idea as to the road environment i.e. are they urban or rural roads?

·         If travel time is distance/speed you need to do the following

·         Create a new field in your table (called travel time – presume hours) I will ignore for simplicity the fact that roads have traffic signals, stops (you need to normally factor in these time penalties , right turn penalties etc.)

·         Populate  the field with a travel time using – Travel Time = D/S (D= distance - km, S= speed –km/h) you should have a field populated for each road link – you should have a very small number – you may want to change your road units length to meters and your time to minutes

·         Test your results against some known travel times and adjust your travel times by taking 30-40% of the posted speed for peak periods and say 60%  for off peak periods. Just keep creating new fields with different factors and keep populating different % fields.

3.       I would create a selection set of the road links that make up your route, Origin to Destination, export to a dbf or similar, manipulate your data and start testing your inputs/outputs,  preferably against some know data.

I hope this assists with what you are required to do, given that you appear not to be  familiar with routing etc.

Regards

Rodney Steinhofel (GISc T, Pr S Arch T)

PBS Consulting

E-Mail:                    rodney at pbs-sa.co.za <mailto:trudieu at stbb.co.za> 

Cell:                         +27 (0) 83 435 3192
Phone:                     +27 (0) 21 843 3456

From: africa-bounces at lists.osgeo.org [mailto:africa-bounces at lists.osgeo.org] On Behalf Of Uazukuani
Sent: Tuesday, January 15, 2013 3:31 PM
To: Rainer at krugs.de; Africa local chapter discussions
Subject: Re: [OSGeo Africa] Travel Time Calculation

Hi Rainer 

I have worked with GRASS before and will check that out too. 

I don't think I will manage R on my own so I will pass. 

rgds,

Uazu

On Tue, Jan 15, 2013 at 11:04 AM, Rainer M Krug <r.m.krug at gmail.com> wrote:

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On 15/01/13 08:24, Paul Scott wrote:
> On 15/01/2013 08:53, S Coetzer wrote:
>> Hi
>>
>> If I can suggest a quick an easy way to get estimated time travel.
>>
>> Get your x,y coordinates from point A to point B and plot it on Google maps. Use the GET
>> DIRECTIONS facility, this would give you an estimated travel time and distance along with
>> several possible alternative routes.
>>
>>
>
> For a group of GI professionals, I am bitterly disappointed in these types of answers. Has
> anyone heard of Djikstra's algorithm (http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm) or
> a* or Shooting-Star distance algorithms?
> (http://www.policyalmanac.org/games/aStarTutorial.htm)
>
> From that, we can infer that distance * average speed = time right?
>
> Come on ladies and gents! Let us foster an environment for new thinking and innovation, not a
> forum for consumption of predefined OTS products.
>
> OSGeo = Open Source = hack and pick and modify = change = new = better = share.

Well - if there are "out of the box" solutions, why not mention them so that they can be used?
Easier in many regards (although not that satisfying and challenging...)

But here are two ideas:

1) You could use R. I wouldn't wonder if there is a package for that.

2) Use GRASS:
a) Rasterize your road network (NULL values for "not on road")
b) use r.cost or r.walk to calculate the least cost paths along the road network (see
http://casoilresource.lawr.ucdavis.edu/drupal/book/export/html/96 "Simple Comparision of Two
Least-Cost Path Approaches" for a comparison of the two)

Warning: I haven't used this approach yet, these are just ideas, but they could work. To get motre
info, I would suggest to google and ask on the GRASS user mailing list.

Cheers,

Rainer

>
>
>
> _______________________________________________ Africa mailing list Africa at lists.osgeo.org
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- --
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys.
(Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

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