Jim the planners (and board members) you've talked to have more sense than the ones I know.
I once heard one of our planning board members ask how tall was the tallest ladder on a fire truck if the ladder was fully extended. He said he wanted to know because he wanted to make the required width of a subdivision road wide enough so that if the fire truck turned over with the ladder extended the ladder wouldn't be off the road.
I know, insert face palm here.
Larry P
There are pluses and minuses to working in a large metropolitan area; one of the pluses is that, generally, you interact with professionals rather than amateurs.
> ....If anyone could tell me what the reason is for this regulation, I may be able to ask for an exception....
It's going to have to do with how many houses and people would be trapped if a burning/leaking tanker truck or crashed airplane or marauding godzilla blocked the sole access in and out of your proposed development.
You asked about what the radius should be used. Which radius? R/W, edge of shoulder, edge of pavement, face of curb? If there is not curb/gutter/sidewalk required, will the design allow for future improvements?
Is this a residential subdivision or commercial development? If the public works does not have standards, the planning department may. Usually the fire department has requirements for turning radiuses as well.
This can't be the first cul-de sac built in this area...They may not have a standard for the r/w radius, but I bet they do for the improvements built within it.
I would probably reference the AASHTO Green Book, "A Policy on Geometric Highway Design" as ONE of my guides.
As someone also stated, a 60' R/W along the road ,60' reverse curve, and 60' radius within the cul-de sac, will usually get you a 50' radius to the face of the curb. This is usually a min. turning radius.
Sorry, I should have given more info. It will be a 30' wide TOTAL right of way. It will be a one way loop. The road width will be 20' or so. The rest of the RW will be surface drainage quasi ditches.
It is a redneck subdivision, with 'lectricity, city sewer, and city water!
N
So if I plan on making large lots, then that would be less people trapped and maybe....
Make the whole thing an easement.
I pulled our local City standard drawings to check. For an urban culdesac they have a 40' pavement radius and 55' to the property line. For rural ones it's 43' and 60'
There is a neighbourhood not far from me with a whole series of these one-way loop culdesacs. I checked several of them in Google Earth. It looks like they all have a 75' diameter for the pavement and 30' diameter for the inner grassed island.
Reading your post again, it sounds like you're designing a crescent instead of a culdesac.
Here is a page from Ramsey & Sleeper, Architectural Graphic Standards, 6th Edition, in two parts due to losing some of the edges during the scan. This may be of some help. Firetrucks may be a different requirement altogether. If you don't have this book, I would suggest you add the latest version to your library. There is a lot of good information in this book.
For a cul de sac:
If the local authority does not provide cul de sac information, you should refer to Appendix D of the international fire code.
A simple cul de sac is usually a 96' diameter drivable surface, but there are other (cheaper) alternatives contained within the document.
As far as corners or intersections, AASHTO standards are safe, and the radius is dependent upon the design speed. AASHTO standards (at least around here) are typically more stringent than county standards.
From memory, I believe that a 50' C/L radius design was an acceptable minimum for 15 mph.
This plat is nuts
Be careful how you lay out your curves...
We got a fire truck to come out and make a turn. Measured it. It was 50'. So, we made it 60'.
Our standards for S/D are easy. Collector street, 40', arterial street, 50', main throughfare, 60'.
I make all streets 50', unless they need to be bigger. Most of the s/d's we do aren't all that intricate and very few have streets coming off and entering one's we are designing, so 50' works with a 60' cul-de-sac. The first one I ever did lapped over two jurisdictions (chapter 242 of the local government code) and we made all the streets 60' just to keep everyone happy.
This plat is nuts
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