One SF dwelling = how many cars?

[maximov]

A developer has informed our town planning commission that he would like to build a cluster development across the river from our old town center. The proposal includes a bridge that would be accessed from a leg off the narrow residential street that runs the four or five blocks by our post office, town hall, church, park, and various older houses to the state highway. As far as I can tell, at most times of the day this street is traveled by more bicycles, horses, dogs, cats and small children (usually right down the middle) than cars. I can imagine this will create some problems, and I'm not sure there isn't a better alternative. However, I would like to get an idea how many cars the 64-house project will add to the traffic. Is there a rule, like 2 cars per home? Don't yet know what sort of homes they will be ($125 K? $500K?).

I did try searching for the answer to this question in the forums, and found discussion and links about road capacities (which reminded me again of my ignorance: what is LOS? ADT?). Anyway, thanks!

 

[jordanb]

Here, it's 2 cars per SFU, 1 car per MFU, reducable in some circumstances.

 

[ludes98]

Here, it's 2 cars per SFU, 1 car per MFU, reducable in some circumstances.

The question is how much is generated not what is allowed.

Maximov the problem is not just how many cars, but how many trips. Traffic people talk in trip counts. While there may be one car, if everyone in the family uses it maybe there are 5 trips per day. ADT=Average Daily Traffic LOS=Level of Service Hopefully some transportation planners can help with trip counts generated by a single family residential use.

 

[maximov]

The question is how much is generated not what is allowed.

Exactly right, sorry, jordanb, if I was unclear.

Trip counts, yes, that makes sense. Thank you for explaining the acronyms, ludes... but still confused about LOS: level of service provided by... the road?

 

[nerudite]

Exactly right, sorry, jordanb, if I was unclear.

Trip counts, yes, that makes sense. Thank you for explaining the acronyms, ludes... but still confused about LOS: level of service provided by... the road?

Level of Service can mean different things in different communities, and it often does. Sometimes LOS will depend upon how many vehicles a road segment can handle per day, sometimes it's capacity during peak times. Some jurisdictions set LOS by intersection and the wait time for getting across the intersection or capacity volumes at an intersection. One municipality I worked for had the weirdest LOS I've ever seen: average speed times between points on specific roadways. If traffic was going to increase travel times between Point A and Point B, then it would get a failing mark (LOS F). If you want to know about LOS on a certain road, you should probably contact your municipality to find out what traffic levels have been adopted at each service level and what is considered 'acceptable'.

The number of trips can vary upon the type of development. Most jurisdictions in the States rely upon the Institute of Transportation Engineers Trip Generation Manual. It is pretty technical and has a lot of variables. Also, each municipality decides on what they allow within the calculations. So you will likely need to talk to the municipality and see what their requirements are... maybe they have already required a transportation impact analysis that you can review.

 

[cololi]

trips generated by single family dwellings vary from place to place. In the community I work for, a single family dwelling generates right around 10 vehicle trips per day. Multi family dwelling units generate anywhere from 4-7 trips per day, with the most dense developments generating less per dwelling unit. Check the publication Neuro mentioned to get a good idea.

 

[jordanb]

My bad. I didn't read carefully enough.

 

[Chet]

I read it the same way as jordanb the first time. Max, I think cololi and neutro have put you in the right direction. As others mentioned, the real imapcts vary from place to place, availabiity of transit options, etc. but absent of an expensive study, run with the rules of thumb mentioned here.

 

[Gedunker]

In the community I work for, a single family dwelling generates right around 10 vehicle trips per day.

This is the number we use as well.

What kind of pedestrian connectivity will there be between the development and the town center? Good connectivity can reduce trip generation.

 

[maximov]

I'm guessing that since our town has no real services (pop. just over 400) that the trip count might average a little less than in a place where you can jump in the car to go to Pizza Hut or Hollywood Video on a whim. But even if it's half, 320 trips per day would surely change the character of the sleepy neighborhood through which they all drive in a big way, wouldn't it? Or would it? They COULD build a road directly from the state highway to the new neighborhood; it would just cost more.

What about the objections of people who bought their houses on a dead end, and now will be on a well-traveled street? I guess that happens all the time... I had to open a 30-foot long barbed wire gate to get to my house in the dingweeds when I first built; now I live on a pretty busy paved road ("Who's here?" I still think whenever a car comes by), and not a cow to be seen.

What kind of pedestrian connectivity will there be between the development and the town center? Good connectivity can reduce trip generation.

That's a really good point. Could the town encourage them to design the new part of the road (through the sandy desert from the bridge to the development) to be really attractive to pedestrians; maybe even to put a paved trail beside it? This might make a bigger difference in the future if the main street I'm talking about becomes more of a village commerce area (as I would like to see happen). But right now, there are no businesses there. And it will be a very long walk, I'm guessing, from where the houses will be clustered to the bridge. Still, kids will ride their bikes to the park and some serious walkers may hoof it to the P.O.

Sorry, coffee makes me go on and on. Thank you all.

 

[boiker]

trips generated by single family dwellings vary from place to place. In the community I work for, a single family dwelling generates right around 10 vehicle trips per day. Multi family dwelling units generate anywhere from 4-7 trips per day, with the most dense developments generating less per dwelling unit. Check the publication Neuro mentioned to get a good idea.

Are these considered origin trips or origin/desitnation trips? 10 trips originating from a single house per day seems high. Even 4-7 seems little on the high side. If these are total number of trips to this property...either as a origin or desitination it seems more plausible.

 

[nerudite]

Are these considered origin trips or origin/desitnation trips? 10 trips originating from a single house per day seems high. Even 4-7 seems little on the high side. If these are total number of trips to this property...either as a origin or desitination it seems more plausible.

10 trips per single family DETACHED unit is an average recognized by most municipalities (and it used to be the average quoted in the ITE manual, but I haven't looked at one of those since I moved to Canada). It's not high when you really think about... because it includes all trips, both coming and going, by all people in the house and visitors. Trips to work and back, trips to the store and back, the mail man, the UPS driver, the pizza delivery guy... there are a lot of trips to our houses that we never think about. It seems to be pretty close to reality for most suburbs at least.

 

[DennisMaPlanner]

ITE Trip Generation Handbook 6th ed. has a SFU with an average of 9.57 trips per du. The range is 4.31 to 21.85. This use to be a little over 10 in past editions but has actually dropped. The description includes the following comments:

"As expected, dwelling units that were larger in size, more expensive, or farther aaay fromt he CBD had a higher rate of trip generation per unit than those smalle rin size, less expensive, or closer to the CBD. Other factors such as geographic location and type of adjacent and nearby development may also have had an effect on the site trip generation."

Morning peak hour is 0.75 with 25% entering and 75% exiting (7-9 am) and afternoon peak hour is 1.01 with 64% entering and 36% exiting.

 

[cololi]

What nerudite said. I figured my own household trips per day for a project when I was in school. Over a 15 day period, the house I lived in (including my roomates) generated 26 vehicle trips per day, and we all walked or biked to school.

 

[Hedwig]

trip generation

Our town uses the usual figure of 10 trips per household. But it is useful to consider the demographics of the new neighborhood. Around here, some of our low-income housing contains multiple families, groups of single working people and extended families-- so you see trailer parks crammed with 3 to 6 vehicles per home. (Of course, not all of the vehicles are in working order). The thing is, life is complicated and our public transit is rudimentary, so households generate a lot of trips-- probably more than the rule of thumb recognizes. If I were in your shoes I'd promote a separate road for the development...More traffic means reduced quality of life: air pollution, noise pollution, hazards to kids and other pedestrians. Traffic is a big issue in our neighborhood-- the narrow historic road I live on is one of the few east-west routes, so it now carries over 10,000 trips per day, and even if all the arterial roads currently gathering dust on plans were built, the traffic is still expected to increase by my house to over 13,000 trips per day by 2020. This road is 24 feet wide; our house is about 10 feet from the road. I'd do just about anything to reduce rather than invite more traffic, especially the significant volume of heavy industrial stuff...

Quijote

 

[H]

we use 10.

 

[maximov]

by nerudite:

the pizza delivery guy...

I WISH!

Thanks, very useful info, all. Quijote, maybe it would be better to encourage them to build a new road, even though the current plan might force the issue of making the main street into a business area, which I personally think could be a good thing, if it was done right. But it seems at least a few residents are (understandably) horrified at the idea. Anyway, the next meeting should be interesting...