What values do you use when calculating clear sight distances for residential driveways? Driver eye height, object height, etc.? References would be helpful.
Here it varies by county. But the one I like goes like this.
Drag tape 300 feet each way and pound a lath next to the pavement so it is 3' tall. Stand in proposed driveway at edge of shoulder with your eye at the top of a 4' lath. If you can the top of the other two, it's good.
But you should check with local road commission or controlling agency.
Been a while since I've physically checked site distance in the field and I recall the old object height (6-inches) was done away with sometime in the early 2000's.
I believe your resource is the FHWA "green" book.
Driver eye: 3.5'
Object height: 2'
For stopping site distance.
*** you need to confirm with current edition of green book ***
We used 1" sticks of PVC, cut to height. Went to the field with a partner. Put one man at the driveway in question. Other moves up/ down the road until the site limit is found (point immediately before clear recognition of person/ PVC is not possible at the prescribed heights). Measure and report.
> What values do you use when calculating clear sight distances for residential driveways? Driver eye height, object height, etc.? References would be helpful.
https://bookstore.transportation.org/item_details.aspx?id=2188
Thank you for the information, I am aware of AASTO publications, etc. I am dealing with vague town requirements which reference terms not present in the green book. I am just looking for input from others as to methodologies they might use.
Your DOT may have requirements if on a state road
> What values do you use when calculating clear sight distances for residential driveways? Driver eye height, object height, etc.? References would be helpful.
That falls under engineering in any city, county or state I've worked in. Why would a surveyor want or need to know this? Just curious.
This is required info for driveway permits for a subdivision I am working on. I am trying to get things done while the engineers dither away on their pet projects.
> > What values do you use when calculating clear sight distances for residential driveways? Driver eye height, object height, etc.? References would be helpful.
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> That falls under engineering in any city, county or state I've worked in. Why would a surveyor want or need to know this? Just curious.
It requires measuring; something we surveyors do. The County or State gives us the requirements, we show if the site or proposed design meets them.
There are lots of twisty roads with short stretches between the crests and intervening low points here in hilly Dutchess County, NY. Sight distances for driveways and access roads for new developments are a big deal on State, County and even Town roads. While some sites are no problem because it is very obvious the sight distances exceed the minimum requirements, it is often difficult to meet all the requirements due to the twisting road and vertical profile, especially keeping the line of sight 6 inches above the surface of the road. At locations where the sight line crosses an area that is not paved, I have had to meet a foot clearance to allow for grass and snow.
It is easy to see how far one can see, but it is hard to see how far and still know where the line of sight is relative to the road or ground one is looking over. Where things are tight I have done a detailed topo and then cut sections and plot profiles to ensure the proposed features will work with the needed clearances. Sometimes the profiles are the ONLY way to show the proposed grades will work when built. A time consuming process, but it works.
Ken
Ohio DOT Location and Design Manual Intersection Sight Distance (PDF) http://www.dot.state.oh.us/districts/D08/Documents/Permits/Intersection%20Sight%20Distance.pdf Takes into account speed of approaching through traffic, obstructions to "clear sight triangle" and vertical curves.
I would also look at NH Highway Design Manual Chapter 3 Page 3-14... and the APPLICATION FOR DRIVEWAY PERMIT - New Hampshire (PDF)
The NH Design Manual references the AASHTO A Policy on Geometric Design of Highways and Streets "Green Book" throughout the NH DOT document.
My experience has been that the local, County or City, Highway Engineers may adopt the state standards with a provision that the "design speed" is the posted speed limit plus a percentage of the posted speed limit to ensure safety of design. You should check with your engineering department and/or the engineering department that will be reviewing the subdivision design for their requirements.
Yes, I'm aware of the importance and complexity of sight distances. It's just unheard of for a surveyor (in my experience in 3 states) to be involved in it above the initial topo work. Around here they call that falls under Professional Engineering.
6" Object Height & Driveway Sight Distances
The 6" object height is most often used for "stopping sight distance". It is to allow you to stop before running over an object laying on the road. I always thought it was prudent that you check every can of beer on the pavement. It makes no sense to run over a full can.
"Driveway sight distance" uses 3.5' or 4' for the eye height of a driver and 3' for an approaching vehicle such that if you cannot see it you most likely can be out of it's way before it gets to where you were when you entered the roadway.
Paul in PA
> It's just unheard of for a surveyor (in my experience in 3 states) to be involved in it above the initial topo work. Around here they call that falls under Professional Engineering.
Generally states in the east and northeast statutorily define the practice of land surveying to include more design work. In Maryland I can design road and street grade plans, sediment and erosion control plans, and storm drain and storm water management systems.
To sit for the PLS exam you need either two years of design experience or 12 semester hours of hydrology and design classes. Then in addition to state law there is a four hour storm drain and road design exam.
6" Object Height & Driveway Sight Distances
I have used 3.5' (driver's eye) to 3.5' (driver's eye) for corner sight distance when a vehicle is pulling out of a driveway.
That probably either came from AASHTO Green book or the State highway design manual.
Highway Design manual does not take into account city/county roads very well. I prefer the AASHTO Green book.
