A question I am frequently asked is about passing and no-passing markings on our highways. I often get comments describing a particular location on some highway where the center lines allow for passing, and the person doesn’t think it should be allowed. I will try to explain the accepted criteria for determining whether the lines should allow for passing or not.

The national Manual on Uniform Traffic Control Devices spells out the requirements for establishing passing or no-passing zones. The New York State Supplement to the MUTCD also governs markings in New York state.

On two-way, two- or three-lane roadways where there are center line markings, no-passing zones are established where passing must be prohibited because of inadequate sight distance or other special conditions. Adequate or inadequate sight distance is further described below.

First, let’s define two terms: vertical and horizontal curves. A vertical curve is where there is a change in elevation, such as a hill. A horizontal curve is where there is a change in the forward direction, or a curve that must be negotiated safely. The sight distance for both types of curves is based on the 85th percentile speed (the speed that 85 percent of free-flowing vehicles are traveling at or below) or the posted speed limit. Table 3B-1 in the MUTCD gives minimum passing sight distances for various speeds. The higher the speed, the farther you need to be able to see an oncoming vehicle. It should also be noted that sight distances are measured in both directions, which is the reason passing may be permitted in one direction but not the other.

In the case of a vertical curve, the sight distance is based on the distance at which an object 3.5 feet above the pavement surface can be seen from a point 3.5 feet above the pavement. If this seems complicated, it’s not as bad as it appears. A car driver’s eyes are approximately 3.5 feet above the pavement, and an object that is also 3.5 feet above the pavement can be easily recognized.

Similarly, the passing sight distance on a horizontal curve is the distance measured along the center line between two points 3.5 feet above the pavement on a line tangent to the embankment or other obstruction that cuts off the view on the inside of the curve, such as a building or tree line.

The MUTCD also prohibits passing on approaches to obstructions in the middle of the road (pedestrian island, for example), on approaches to railroad grade crossings, and at lane reductions. The minimum length of a no-passing zone is 400 feet on high-speed roads and 200 feet on low-speed urban highways. Also, there may or may not be signs accompanying the markings – a “no passing zone” pennant on the left in a no-passing zone, or “pass with care” on the right in a passing zone. If successive no-passing zones are less than 400 feet apart, no-passing markings should connect the zones, regardless of sight distances.

The point to take from this article is that passing and no-passing zones are not arbitrarily determined. They are based on engineering studies in concert with national standards according to speeds and sight distances. If you feel there is not sufficient room, wait. You never have to pass just because pavement markings allow it.

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For more articles on traffic law and traffic safety, visit the Traffic Safety Board website at www.franklincony.org and click Traffic Safety Board under “Departments.” You may also contact me by email at dwerner151@verizon.net or call me at 518-483-1882.