Radius in subdivision streets 1

[uncivilized]

In my firm we always design interior subdivision street 25' wide (including curb and gutters). Intersecting streets have a curb radius of 25'. I was walking through an old section of town and noticed that the curb radius was much smaller, probably between 5' and 10'. It made it a lot easier to cross the street. I have been thinking about reducing the radius for my next design but was worried about bus traffic. Does anyone else have any thoughts about this.

 

[francesca]

Smaller radii are also difficult for cars to corner. You might want to post this in the Traffic Engineering forum, to attract the correct attention, as they can quickly tell you what's difficult for a car to navigate.

We designed subdivision roads either 28' (back of curb to back of curb) or 24' (boc-to-boc), with 25' corner radii. This was the planning commission/street department minimum, contained in the subdivision regulations.

I wouldn't go lower than 25' personally because it always annoys me when right-turns are difficult to make merely because of the damn turning radius. Depending on the type of neighborhood, school buses might be a serious consideration.

 

[RDK]

Locally we use a 7 m radius. We also use barrier curbs with a 1 m transition to the curved portion. If sidewalks then we use a dropped section in the barrier curb for pedestrians.



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[francesca]

7m ~= 23ft

 

[ACtrafficengr]

Make the corners too tight, and larger vehicles (busses, delivery trucks, snowplows, emergency vehicles, etc) start having problems. Make them too big, and pedestrians are exposed to traffic more due to longer crossing distances, cornering speeds go up, etc. 25-30 feet seems to work in residential areas.

As RDK says, you can go smaller using a tapered offset or 3-center curve. You can also reduce the radius if you have striped parking lanes, since the effective radius is a three-point curve tangent to the edge lines and the center of the corner curve.

------------------------------------------
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[roncity]

The reason the tight radius works in the old part of town is that the streets are wider than the new subdivision with parking lanes on both sides. Longer vehicles ( bus , garbage, delivery trucks ) typically complete their turn by encroaching over the lane next to the centerline.
Putting short radii on narrow streets means the rear wheels of turning vehicles track over the curb ….or they encroach into opposing lanes of traffic.

Bottom line: don’t design any radii unless you check it with turning templates

 

[uncivilized]

Thanks to all that answered. Looks like we will stay with 25' in most cases.

 

[saruman26]

Just for reference, Arlington County Virginia and Fairfax County Virginia allow for 15 ft radius curb returns on residential streets and in subdivisions, with minimum street width around 26 ft FC to FC. This works rather well to provide easier pedestrian access while not excluding the occasion WB-50 from the area.

 

[rossmail]

it is set by the turning radius of a fire truck ,call the local fire hall and they will tell you what they want ,they are the ones that set the radius requirements .