Driveway Sight Distance

[dficker]

I'm double checking sight distance for a drive adjacent an overpass of an expressway. Drive is on the overpassing road right off the bridge approach, and can't be relocated.

The typical intersection sight distance has the car set back a certain distance from the crossing road 15' or so while it waits to enter the main road.

Is it safe to assume at the private drive the vehcile will pull up as close to the intersection road as possible to see (esp. since they are used to pulling out of their drive?), if so how far can I assume the driver's eyen be back from the edge of the road (IOW whats the typical horizontal dimension used from front of car to the driver's eye)? I have heard 8' but want to confirm what others use. I am in Ohio.
TIA
Dan Ficker, PE

 

[TerryScan]

According to one handbook:

http://www.ctre.iastate.edu/pubs/traffichandbook/4SightDistance.pdf

the sight triangle vertex would be 10' back from a stop bar at a stop controlled intersection.

Upon a search:

http://www.state.nj.us/transportation/eng/documents/RDME/figure6a.shtm

has a figure which adds your 8' to a desired 10' (6.5'min) from the travel lane.

 

[dficker]

Thanks, confirms my 8' horizontal dimension from front of car to driver's eye
However, this is a drive (what I didn't say is that its for a SF residence), IMHO I don't think the driver would wait to enter the road from 10' back from the travelway.

 

[TerryScan]

How far back do you think he will wait? The document stated a 6.5'min. Do you think he will be closer? The min. sounds close ro right to me.

 

[ACtrafficengr]

Lacking additional info, I'd use a full-sixed pickup/SUV for the design vehicle for a residential drive, since it's the largest vehicle that can be expected to use the driveway on a frequent basis.

AASHTO says 14.4' from EOP to eye for intersections. If the driver is in a pickup/SUV/Buick Roadmonster, this is probably realistic, given an 8' setback from bumper to eye position (

http://www.tfhrc.gov/safety/pubs/03082/08.htm

says 86.4" from headlights to eye). Add the 6.5' bumper-to-EOP setback from the NJ document, and you're pretty close to AASHTO.


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"...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

 

[dficker]

Thanks for the replies.

I guess the point I am trying to get across is that, on a sight distance constrained driveway (say one thru an opening into the guard(guide)rail); would the driver not pull up as far as he can and not sit back the 14.4' or so from the eop- esp. given the driver's familarity with their drive.
Low speed (35mph) township road, BTW

 

[nutbutter]

You're right. They could be pulled halfway out into the street to try to see if they can pull out, but that's generally not safe. I have to do it every morning at one intersection on my way to work.
It's probably best to design using minimum requirements at the very least.
Peace,
Stoddard

 

[ACtrafficengr]

Could you raise the driveway profile so drivers can see over the approach rail?

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"...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