How We Use the Safe Line Study

One of the most common impacts for ROW projects regards the possibility of proximity damage to a dwelling. The safe line theory is one way that ROW appraisers determine if proximity damage exists. 

Proximity damage is the impact to a residential property when the right of way, or roadway, moves close enough to a home that the market recognizes a diminution in value. The article “The Long and Winding Road: A Cause for Proximity Damage” by Richard E. Welch was published in Right of Way Magazine in 2009. It discusses the theory in detail and in summary it is the “front yard setback on existing and new homes. This setback is either on the subject’s roadway or a comparable roadway.”

The ‘safe line’ itself is the point of movement that the road can move closer to the dwelling. That is, until “the resident is not adversely affected by noise and reduced privacy to their home’s proximity to the roadway.” Welch indicates that it is essential to “evaluate a large sampling of homes along a roadway before determining the safe line distance for that specific area before beginning any new construction.” So how has North by Northwest used this principle? 

How has NxNW Used This Principe? 

The reality is that roadways and right of way projects move roads closer to properties all the time. Stakeholders often make the erroneous claim, “If a road moves a foot closer then the property is damaged.” But this is often not the case. Imagine a scenario where the property had 1,000 feet of front yard before the road. In this situation, the road moving one foot closer will likely have zero impact. Nonetheless, stakeholders are rightly concerned with the negative damage to the property due to the proximity of the roadway. The appraisers’ job is to determine the impact to market value, which is relative to the property type.

We assess this information from the safe line study. As stated previously, the safe line study is done to assess the threshold at which proximity damage exists in a specific market. The norms for setbacks are different for different markets.

In one instance, North by Northwest used the safe line study on a project in Mecklenburg County, NC. To determine the safe line we looked at recent construction in the area. Here is what we found in this particular project:

Safe Line Theory: Mecklenburg County

To estimate the subject’s safe line, a survey was done of single-family residences with side yards along Weddington Road. We also evaluated two other road corridors with similar traffic and speed limits in the subject’s market area. The two additional study areas selected act as feeder roads, much like the main subject’s roadway corridor. 

First, North by Northwest measured the distances from the right-of-way to the outside living area wall of each residence. The measurements indicated that the side yard setbacks varied widely. It turned out that the wide range was a result of variances in zoning ordinances and development standards. Therefore, lot sizes, as well as dwelling sizes, were very varied.

To more closely match the subject’s effective lot size and location of the single-family residence on its site, the lower quadrant of properties was examined. The table below lists five of the lowest distances from side yards facing residences along the subject’s corridor. It also shows five of the lowest distances of residences from two similar corridors. 

Measurements identified the distance from the nearest heated wall and the right-of-way. The lot size, home size, and year each residence was built were added. This illustrates that the homes selected vary in lot size, square foot of living area, and age. The homes identified in this analysis vary in age from 1988 to 2014. There does not appear to be any correlation with respect to the age of the home and the proximity to the right-of-way. Homes constructed more recently are located within similar proximities to the right-of-way in the Matthews market area as are residences that are older.

Conclusions Drawn in Mecklenburg County

A side yard setback range of 20 to 50 feet. With an average of 37 feet. This is eight feet under the minimum front yard setback for a single-family residence in the subject’s zoning district. The premise of the safe line theory is that no builder would construct a new dwelling inside the safe line, and therefore have a new house with built-in external obsolescence. The safe line estimated for roadway corridors similar to the subject’s corridor is 37 feet; the average from the chart above. 

Single-family residences with a side yard setback of 37 feet or greater are beyond the safe line for the immediate neighborhood. They are a market acceptable distance from the right-of-way. The market begins to see properties with a setback closer than 36 feet as less desirable. This is because of potential noise, safety, and reduced yard size. The closer the dwelling setback comes to the right-of-way the less desirable the property becomes.  

And so, if the ROW moves but doesn’t cross this line then there is no impact recognized by the real estate market. For newly developed housing the safe line study helps appraisers determine damages. It also indicates where the market starts to recognize those damages. But does the safe line study work everywhere? 

Does one safe line work the same everywhere? 

The answer is simple, no, it doesn’t. The safe line study sets the bar for residential areas with a more or less homogenous housing stock. It’s a bit different if you’re in a rural area with large pastures or rural boutique farms. Then the safe line study may not apply. Nor does it work with commercial properties. Because, in our experience, damages to stem from changes in utility versus moving the road closer to a commercial building. 

Safe Line Theory: Dare County

In another example, where North by Northwest estimated the subject’s safe line, a survey was done of 40 front facing single-family residences along Colington Road in Dare County. As before, measurements indicated that the front yard setbacks varied widely along Colington Road. The wide range is a result of the lack of controls on development before zoning was adopted.  

Lot sizes, as well as, dwelling sizes vary. And many of the properties along Colington Road today are classified as legal nonconforming. Primarily due to their undersize lots and or their setback being less than current zoning requirements. These parcels have been grandfathered.  To more closely match the subject’s effective lot size and location of the SFD on its site, the lower quadrant of properties was examined.  The table below lists ten of the lowest distances between the most front facing heated wall and the existing right-of-way as indicated by the NCDOT plans for this road project.  

Comparing the Conclusions Drawn in Dare County and Mecklenburg County

As you can see the two markets are different. The safe line in Dare County is particular to its market with an average of 31’ feet from existing right of way versus 37’ in Mecklenburg County. 

Ultimately, safe line study works in residential areas and is a much more in depth and informative approach to understanding what the market shows than traditional methods like relying solely on residential zoning codes. You can read more about this in our next article “Determining Proximity Damage to Dwellings.” 

Using market evidence for damages is important to North by Northwest because a) it is good appraising, and b) it is important to our clients. Our clients have to negotiate with property owners. Those negotiations go much better when the right of way agent can point to hard data regarding proximity damage, which in turn helps keep projects moving down the (right-of-way) road.

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