150-Mile Radius Exemption Clarification

There is a discrepancy among mapping software and websites as to whether they compensate for the curvature of the earth. The discrepancy ultimately affects whether the user should enter 150 miles when creating a radius or 172.6, based on the conversion from air miles to statute miles. This issue arises from a new entrant safety audit conducted in 2025, on an agricultural motor carrier using the 150-air mile exemption to hours of service found in 49 CFR 395.1(k). The auditor submitted the audit using 172.6 miles, and thereby exempting the carrier from HOS. He was told by FMCSA to use 150 miles. Upon further research, it was determined there are multiple mapping methods. One of the most common, used by Google maps, is called the "World Geodetic System," and commonly referred to as "WGS84," which computes distances based on longitude and latitude. With regard to the radius tool, this same system is applied which compensates for the curvature of the earth. Therefore, when using software that uses the WGS84, the user would simply enter 150 miles, as the curvature has already been compensated. I attempted to do research to determine which software and website uses which systems. This is very difficult as most websites do not declare what system they use. It seems most compensate for the curvature of the earth and likely use the WGS84. This assumption is based on running the same radius map on multiple websites and getting the same results. I contacted Garmin, a world-renowned leader in global positioning systems, with a strong presence in the aviation industry. According to their cartography system, their systems convert everything to WGS84. I contacted two Kansas universities and received a great response from a cartography professor at the Kansas State University. Her email response and explanation is attached in PDF to this issue request. The professor confirmed the use of the WGS84 system but also demonstrated there is far more to this issue. She explained there are two types of coordinate systems, and went on to explain there are often discrepancies in the news when the systems are misused. She further explained even local governments when creating GIS maps can be off significantly.

The problem arises for both law enforcement and industry. In law enforcement, we always "err in the violator's favor," that is, give the benefit to the driver or motor carrier. That is a logical conclusion during normal roadside enforcement activities. We would rather allow a driver to go without a log book when it's too close too call than declare a driver out of service who may have been subject to an exemption. However, when something bad happens, like a fatality crash, and a driver and/or motor carrier is involved who has historically been told they don't need a logbook because we erred in their favor, but upon further review they were NOT within the 150-air mile radius, now that driver and carrier are in a position to be civilly and possibly criminally liable. The issue is a difficult one for those who are providing commercial vehicle guidance to industry when they are so close to the 150-air mile radius. As such, the justification is that we must be consistent in what we do and how these rules are enforced nationwide. We can always err on the side of the driver or carrier, but when our leniency leads to misapplication of the rules, it's not fair those those motor carriers, or worse yet, the victim of a carrier not in compliance. These mileages are used in several areas of the federal regulations. Covered farm vehicles, farm vehicle drivers, hours of service, and even the agricultural exception to hazardous materials in 173.5.

I am requesting that the Alliance seek clear guidance from FMCSA as to which mileage shall be used when calculating radius maps. Should 150 miles ALWAYS be used, no matter what? Should the mileage vary depending on which system is used by the radius map used? Is there a way to determine which system is being used each radius mapping tool? Can FMCSA provide a definitive list of websites that are the only acceptable tools to use when measuring a radius? Once guidance is received, this information needs incorporated into the North American Standard Part A training material, instructor, and inspector updates.