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Transportation I am working on a project that requires a trip distribution analysis. What the heck is that?

paiste13

Cyburbian
Messages
238
Points
9
Long story short, I'm consulting for a developer that is building a 100 home subdivision in a small town. The main access point is a state highway. The DOT says they don't need a "full traffic study" but wants a "traffic impact letter". Okay, I think. My AICP brain can figure this out and it doesn't need to be signed by a PE. I use ITE traffic count data all the time at council meetings and I've never had to go beyond that.

I gathered the trip generation numbers as usually. Then the DOT tells me that's all well and good, but they need trip distribution analysis too. I say okay and hang up and quickly look up trip distribution. So it is where the trips generated in our 100 lot subdivision are going? There is no data on that? How do we figure that out? I was told this is a "super quick and easy" letter showing you won't need a full-blown study, but I am stuck. No one here has ever done anything like that and I can't seem to find anything helpful on google. Is there a map that shows trip distribution areas or zones? Do we make up the zones as we go? I am so lost.

And beyond "hire a traffic engineer", I'd like to know HOW these are mad in simple, planner terms. I want to know more about them for the future.

Thanks!
 

DVD

Cyburbian
Messages
15,021
Points
52
Wish I could tell you how to make one. I've only read the results of those things. I remember in school using a gravity model. The end result was something like 85% of traffic turned right and the rest turned left. Helpful, I know.
 

Doberman

Cyburbian
Messages
209
Points
9
Are you using the Green Book or whatever for the Trip Generation numbers? IE X# of housing units in the development*4 daily trips or whatever the green book says a single family home makes per day? I think this is the second step in the 4 step travel demand model. I believe they are wanting to know where these trips are going.

You might could back into this using the Census Journey to Work data. For instance, where do the rest of the folks within this census tract go to work?

Do your or your MPO have access to the TAZs in your metro? There has to be some way to extrapolate the destinations from this development (origins) based on the employment density and distance to each TAZ.
 

Tranplanner

maudit anglais
Messages
7,920
Points
37
yeah, Doberman is on the right track. The trip distribution analysis would take the number of trips generated by the development and assign them to the road network. You don't need to make up a map of zones, ideally the jurisdiction you're working in would have model results by traffic zone that would tell you in broad terms that x% of the traffic in the area your development is located is going downtown, x% to another centre, etc. Which you can use to make assumptions about where people living in your development will be travelling.

The second, and more important part is using planning/engineering judgement and looking at the surrounding transportation network. How would people get from your development to the nearest highway or rapid transit station or employment centre? That gives you an idea of how to distribute your trips at the micro level.
 

Doberman

Cyburbian
Messages
209
Points
9
yeah, Doberman is on the right track. The trip distribution analysis would take the number of trips generated by the development and assign them to the road network. You don't need to make up a map of zones, ideally the jurisdiction you're working in would have model results by traffic zone that would tell you in broad terms that x% of the traffic in the area your development is located is going downtown, x% to another centre, etc. Which you can use to make assumptions about where people living in your development will be travelling.

The second, and more important part is using planning/engineering judgement and looking at the surrounding transportation network. How would people get from your development to the nearest highway or rapid transit station or employment centre? That gives you an idea of how to distribute your trips at the micro level.

Thanks.

Shouldn’t he be able to get with his MPO to run something like this? I wouldn’t think individual cities have this kind of access unless the city is basically the entire metro.

If you know the destinations you should also be able to ARC’s Network Analysis tool to determine the corridors impacted based on the way from O to D based on the shortest travel time.

If Transit is available I think you can assume a 1% modal split as standard, but I’m not sure.
 
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