Skewed Thinking

The two pictures below show the driver’s view looking north and south at the same intersection in the Town of Farmington: Collett Road (Eastbound) at Hook Road. With all of the clutter, trees and slopes, the view to the north looks more dangerous than south, doesn’t it. Believe it or not, there are more accidents due to the cars coming from the south!

Driver’s view (looking north) of the intersection of Collett Road (Eastbound) at Hook Road in the Town of Farmington
Figure 1: View toward the north

Driver’s view (looking south) of the intersection of Collett Road (Eastbound) at Hook Road in the Town of Farmington
Figure 2: View toward the South

The pictures show the driver’s perspective from Collett Road while stopped at eastbound Hook Road.

The Town of Farmington asked Ontario County to do a study of the intersection, and Ed McLaughlin, Superintendent of Highways, asked me to come out and review the report from the County. The report by the County was a great way to get started. The County provided a review of the intersection and gave Ed the facts he needed to help improve the intersection.

While I was there, we looked at the intersection to see if there was anything special that Ed should be concerned about. While there are a lot of details about the intersection and the County’s report that I don’t have room to discuss here, this intersection illustrates a common concern with many intersections.

In our workshop, Road Safety Fundamentals, we recommend all intersections have a skew of no more than 15 degrees from a right angle. If the skew is more than this, it is hard for drivers to look out and see oncoming traffic. While it doesn’t appear to be when standing at the intersection, the two roads are actually skewed 23 degrees from a right angle.

To illustrate why this is a problem, look at Figure 3, the overhead view of the intersection. Eastbound drivers looking to the south on Collett Rd. will have to turn their heads more than ninety degrees to see down the road in that direction, and they may not do so because of their concern with the clutter to the north.

If they only glance at a right angle (90 degrees) from the driver’s seat while stopped at the stop sign, they can only see cars closer than 150 feet to the south. This is far less than the 300-foot sight distance recommended for 30 mph! At this distance, a car traveling at 50 mph would be at the intersection in only 2 seconds!

Overhead View of Collett & Hook Roads
Figure 3: Overhead View of Collett & Hook Roads (image courtesy of maps.live.com)

A sharper skew on an intersection may actually be safer since drivers understand there is a need to take extra precautions. A little skewed thinking may be in order.

The most obvious solution would be to square up the intersection. This may be rather expensive and will take some time to complete. At this particular location it may be possible to work with the land owners to trade land. It might be less expensive to square up a skewed intersection than you think.

Check all of the signage on all approaches to the intersection. An intersection ahead sign may alert drivers coming from the south about the intersection. Even though the sight distance is good, a reminder may help improve safety.

The Town has improved the sight distance to the north at this intersection. They also have stop lines to help the drivers on Collett Road understand where to stop. By placing the lines parallel to Hook Road, the stop lines show the angle of the intersection and alert the drivers to the fact that the intersection is skewed.

Spring 2008

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This work by the Cornell Local Roads Program (CLRP) is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.