Published
The county's own driveway spec: sight distance, angle, grade and an 18-inch culvert floor
The county publishes a driveway spec. Almost nobody reads it.
This site has already covered what the state requires of an approach onto US-20, because Island Park is strung along a state highway and that rule is written down. What is less well known is that Fremont County publishes its own construction standard for accesses onto county roads, and it is more specific than most people expect.
It lives in Appendix D of the county's Development Code, headed County Road Access Management Standards. It sets sight distance, the angle your driveway meets the road at, the grade of the last fifteen feet, the minimum culvert size, and how wide the apron may be by type of use. If you have ever asked an operator “how wide should this be?” and got an answer based on the width of the machine, this is the document that has an actual answer.
The five kinds of driveway, in the county's own terms
Before any dimension applies, the application makes you declare what the driveway is for. The categories are not decorative — the apron width follows directly from them.
| Class | The county's definition, in brief |
|---|---|
| Private residential driveway | Entrance to and exit from a residential dwelling, for the exclusive use of those living there |
| Private collector driveway | Serves a group of dwellings, expressly intended to minimise the number of access points onto the county highway system |
| Commercial driveway | Entrance to any commercial, business or public establishment adjacent to a county highway |
| Cultural or institutional driveway | Churches, schools, hospitals and the like — the code states the design requirements are the same as commercial |
| Minor driveway | Entrance to a field, ranch or farm property, and not frequently used |
The private collector class is the one worth noticing on subdivided ground. A shared access serving several cabins is a recognised category with its own purpose written into the code, and the county's stated intent is to reduce the number of separate connections onto its roads.
The numbers
These are the construction standards a new access has to be built to, once the permit is approved. They are quoted from Appendix D as retrieved on 19 August 2026.
- Sight distance: a minimum of 200 feet in both directions, measured from a point 10 feet behind the intersection of the access with the edge of the county road, and five feet high.
- Angle of intersection: the last 15 feet of the access must meet the edge of the county road at between 80 and 90 degrees.
- Grade: over the same last 15 feet, measured back from the shoulder, the slope must be no greater than 4 percent and no less than 2 percent negative grade — that is, it must fall away from the road, and within a band.
- Culverts: drainage facilities are required for every access, sized by the applicant and approved by the Public Works Director or designee. Where a culvert is required it must have a diameter of no less than 18 inches.
- Staking: access points must be staked and flagged before and during construction, and the stakes and flagging must remain in place until the access permit has been issued.
The grade rule is the one that most often gets missed on a cabin lot, because it is a band rather than a maximum. A driveway that runs dead flat into the road fails it just as a steep one does. The point is drainage: water has to leave the road surface rather than run down your approach.
The culvert figure closes a question the culvert page deliberately left open. That page said the diameter is settled inside the permit, against the county's own roadway standards. This is that standard: eighteen inches is the floor, and anything larger is a drainage calculation, not a preference.
How wide the apron may be
The width at the point where your access meets the county road is set by the class you declared. This is the table people usually guess at.
| Use | Apron width at the county road |
|---|---|
| Residential | 20–30 feet |
| Farmyard or field | 40–50 feet |
| Utility maintenance | 40–50 feet |
| Commercial, one-way | 40–50 feet |
| Commercial, two-way | 50–60 feet |
A residential apron therefore has a floor as well as a ceiling. Twenty feet is the minimum at the road, which is wider than a good many driveways get built, and it is measured at the intersection rather than along the length of the drive.
The requirement nobody expects: a traffic burden calculation
Appendix D asks for something with the application that reads as though it belongs to a commercial development, and does not carve out residential driveways from it.
“A calculation of the daily trip count, trip estimates by hour of the day, vehicle type, vehicle weight, and axle weight of vehicular access to the County highway system must be prepared and submitted with the application.”
— Fremont County Development Code, Appendix D, County Road Access Management Standards, section 1.05.050. Retrieved 19 August 2026
How rigorously that is applied to a single cabin driveway is a question for Road & Bridge, and the honest answer is that this page cannot tell you. What it can tell you is that the requirement is written down, so it is a fair question to ask before you assume a one-page sketch will do. The required sketch itself has its own list: existing and proposed buildings, retaining walls and other physical features affecting the driveway location, property lines and dimensions, existing access driveways, all drainage affecting or affected by the driveway, off-street parking, and the totality of the proposed access.
What happens if you just build one
This part is genuinely serious and it is worth stating plainly rather than in the code's own language. Putting in an access onto a county road without an approved permit is not a paperwork oversight with a late fee attached.
Appendix D says an access created or altered in violation of the ordinance will be posted with a warning notice. A letter goes to the landowner at the time of posting, giving ten days from the date of posting either to secure an approved application or to correct the encroachment. If that does not happen, the code authorises the county to remove the access five days after the notice is complete, to correct any harm caused, to take further action under Idaho Code section 40-2319, and to proceed criminally against the landowner. The county is also entitled to a lien against the real property for any expense it incurs.
So the exposure is not a fine. It is the removal of your access, at your cost, secured against your land. That is a long way from the risk most people imagine they are taking by having the machine cut an entrance while it is already on site.
Three more provisions worth knowing before you sign
- The permit is not exclusive, and it does not fetter the county. The code says the permit does not prohibit the county from using its roads and public places, and preserves the county's right to full supervision and control over them.
- The county may change your access later. Fremont County is entitled at any time to make changes, additions, repairs and relocations of any access within the right of way as necessary for relocating, reconstructing, widening or maintaining the road.
- County time caused by your access is billed to you. The code puts any expense incurred through work done by county employees necessitated by the access at issue at the applicant's expense, and disclaims county liability for damage arising from that work.
None of this is unusual for a road authority. It is simply not what a landowner assumes they are agreeing to, and it is the reason the access question belongs in the site prep sequence rather than at the end of it.
The practical order
If your lot takes access from a county road rather than the highway, the sequence that avoids rework looks like this.
- Establish which class of driveway you are actually applying for, because the width follows from it.
- Check sight distance on the ground before design, since 200 feet each way can be the binding constraint on where the entrance can go at all.
- Get the drainage answer — culvert or no culvert, and what size — from Public Works rather than from the operator, and remember eighteen inches is a floor.
- Stake and flag the access, and leave the marks up until the permit is actually in hand — the code requires them to stay put until it is issued.
- Confirm the apron width against the class you declared, not against the width of the machine cutting it.
- Settle who is filing the permit before the machine is scheduled, and check whether any part of the work also needs the county's excavation and grading permit.
Common questions
How far must you be able to see in each direction?
A minimum of 200 feet in both directions. The code measures it from a point 10 feet behind the intersection of the access with the edge of the county road, at a height of five feet. On a lot with a bend or a rise near the frontage this is often what decides where the entrance can go.
What angle does a driveway have to meet the road at?
The last 15 feet of the access must meet the edge of the county road at between 80 and 90 degrees. A driveway that eases onto the road at a shallow angle, which is the natural thing for a machine to cut, does not meet the standard.
Is there a rule about how steep the end of the driveway is?
Yes, and it is a band rather than a limit. Over the last 15 feet measured back from the shoulder, the slope must be no greater than 4 percent and no less than 2 percent negative grade. It has to fall away from the road, but not sharply. The purpose is getting water off the road surface.
What is the minimum culvert size?
Where a culvert is required, its diameter must be no less than 18 inches. Whether one is required at all, and whether a larger one is needed, is a drainage determination made by the applicant and approved by the Public Works Director or designee.
How wide can a residential apron be?
20 to 30 feet at the point where the access meets the county road. Farmyard or field, utility maintenance and one-way commercial accesses are 40 to 50 feet, and two-way commercial is 50 to 60 feet. Note that the residential figure has a minimum as well as a maximum.
Do I really have to submit a traffic calculation for a house driveway?
The code requires a calculation of daily trip count, trip estimates by hour of day, vehicle type, vehicle weight and axle weight with the application, and it does not exempt residential driveways. How that is applied in practice to a single cabin is a question for Road and Bridge, but the requirement is written down.
What happens if an access is built without a permit?
The access is posted with a warning notice and the landowner has ten days to secure an approved application or correct it. After that the code authorises the county to remove the access five days after the notice is complete, to act under Idaho Code section 40-2319, to proceed criminally against the landowner, and to take a lien on the property for its costs.
Can the county change my access after it is built?
Yes. The code entitles Fremont County to make changes, additions, repairs and relocations of any access within the county road right of way at any time, where necessary for relocating, reconstructing, widening or maintaining the road.
Does this apply to my driveway onto US-20?
No. US-20 is a state highway, so an approach onto it is an Idaho Transportation Department encroachment permit governed by a different rule with different dimensions. These standards apply to accesses onto county roads. Which authority owns the road in front of your lot is the first thing to establish.
What has to be on the sketch?
Existing and proposed buildings and other physical features affecting the driveway location, property lines and dimensions, existing access driveways, all drainage affecting or affected by the driveway, off-street parking that affects the location, and the totality of the proposed access.