OHSA requires fall protection for changes of grade greater than four feet.

State DOT's have policies concerning guiderail installations.

https://www.nysdot.gov/portal/page/portal/main/business-center/consultants/forms-publications-and-instructions/highway-design-manual/chapter-10

For a residential driveway, assuming it's for a privately-owned home, there might not be any standard other than prudence.

Check your municipalities' LDC.

In Central Ohio, there is a group of Code Officials that discussed this very question.  The local interpretation is guards are required adjacent to walking surfaces hence porches and other walkways from a door to the ground would require a guard.  Windows wells meeting emergency egress requirements specifically were discussed and if the adjacent ground were grass or other landscaping, no guard.  Otherwise anything becomes a walking surface and this can be regulated to excess.  Here is a link to their website.  you can search the minutes of the Code Consistency Committee:  http://www.cocoaonline.org   

A driveway is certainly a walking surface from the means of egress to the public way in many cases and you can interpret this as requiring a guard.  You can check with the local building official to confirm they will be required and if now, you may want to recommend this to your client.
 

Don Phillips
http://worthingtonengineering.com

I believe IBC/IRC require a guard anytime a habitable space has an adjacent area more than 30 inches lower. Basic common sense really. Also note that a guard doesn't have to be a "guardrail".  Anything 42" or more high with openings such that a 4" diameter sphere cannot pass through and meeting load requirements qualifies as a guard.

Just so we're all on the same page, what do you mean by a 100' drop? Is this a 100' vertical/nearly vertical wall, or some fill slope? In any case, I would have to back bridgebuster and ask, "What would the DOT do?"

Although OSHA’s fall protection requirement applies during construction, civilperson gave you the answer. Plus, regardless of what codes say, why would you not want to have some sort of protection?

The 100' is just hypothetical, it could just as easily be 32". I think the point is that the IRC is gray in this area.  In hashing this out with local inspectors and the local building department, they say that prior to 2006 there was no specific requirement in the code. Apparently IRC2006 has some provision for guards around walls connected to the house. I only have IRC2003 with me at the moment so I was hoping someone might weigh in with that information.

I think it is an area that the code needs to address. We can say it is logical or a good thing to do and all that, but if it is not in the code it doesn't get done. In posing the 100' hypothetical to the local inspector, he said that it would be left up to the builder as there is nothing in the code requiring a guard.

And for this particular case, I am coming in after the fact to answer the question "was a guardrail required?".

ZCP
www.phoenix-engineer.com

notwithstanding code requirements, I would put up a guard similar to local DOT requirements although maybe not as heavy since you would likely be dealing with passenger vehicles.

Dik