Here in Alberta

Road specs vary from region to region but here in Alberta 22ft for the road surface would be a good width for a secondary rural road; paved or unpaved. To that you would add 14 or so ft for shoulders. Ditches would also be extra.

Here is a link to the Alberta specs diagrams:

http://www.transportation.alberta.ca/655.htm

I applaud you for trying to get this dimension correct. To many layouts have unrealistically narrow roads.

Depends on the prototype

I may depend on the location you are modeling.

For instance, if you're modeling PA, the road would be narroiw, full of potholes and have detours due to bridges being out.

Each State and every country have their Minimun Road width

To find out the width of a single lane Google the state division of Highways or Highway Department for the part of the world your Road, Hwy, or street is located and then look up dimensions and standards.

Considering most cars and trucks are under 7 foot wide, lanes are set as follows in the U.S.A. :

The U.S. Interstate Highway System uses a 12-foot (3.7 m) standard for lane width. 11-foot (3.4 m) lanes are found to be acceptable by the Federal Highway Administration for automobile traffic, but as lane width decreases (9-foot (2.7 m) lanes are found in some areas) traffic capacity and safety decrease. ^[3]. A full-width freeway lane typically has a capacity of 2,000 cars per hour. ^[4]

In the United Kingdom, many lanes are found in the countryside, and most of these lanes are wide enough for one car at a time and often have a lay by for cars to pass. In general, European laws and road width vary per country, with the minimum widths of lanes being anywhere between 2.5 m to 3.25 m (thus comparable to US lanes). [1]

For more information go to the following page      http://en.wikipedia.org/wiki/Lane#Lane_width_and_capacity

Hope this is what your looking for.

Dan

What I have in mind is an

What I have in mind is an Eastern Shortline 50's 60's kind of area such as Virginia, Pa, and the like.So 22 ft appears to be pretty solid. These are great references, thanks for the response from everyone. 

I think roads on model railroads are often compressed in width.

Most model railroaders are limited in terms of "real estate" available on the bench work, so roads tend to be narrowed a bit from prototype.  Besides that, we want to ship our freight by train so we make the roads bad on purpose.

I found a refrence by Lyn Westcott

A quick note:

I was reading through some of my older model railroader magazines last night and found a question and answer about the subject of auto road width and to determine the width they just set two vehicles next to each other and (in HO) they spaced the two cars 1/2 inch apart and added 1/4 inch to the outside of each and measured the width to come up with a two lane country road 2-1/2 inches wide and a single lane road 1-1/2 inches wide

Dan