Stop signs and sight distance at the intersection

Sight geometry affects the sight distance available to the driver.  But what about the basics of stop signs?

Two-way stop control

When determining corner sight distance, a setback distance for the vehicle waiting at the crossroad must be assumed.   Setback for the driver of the vehicle on the crossroad has been standardized and they have designed manuals referred to as MUTCD (Manual on Uniform Traffic Control Devices). This manual explains in detail the following:   an intersection is to be a  minimum of 10 feet plus the shoulder width of the major road but not less than 15 feet.  However, the Federal MUTCD requires that a stop line, if used, shall be at least 4 feet from the nearest travel lane.

Line of sight for corner sight distance is to be determined from a 3 ½ foot eye height at the vehicle driver’s location on the minor road to a 4 ¼ foot object height in the center of the approaching lane of the major road.  Corner sight distance is equivalent to a specified time gap at the design speed required for a stopped vehicle to turn right or left.

For passenger vehicles at two lane intersections, this time gap equivalence is commonly a distance 7.5 seconds away at the design speed.  Longer gaps are required for trucks and buses, and for multilane roads.  Generally, the public right-of-way should include and maintain this line-of-sight.

All-way stop control and signalized intersections

Drivers at intersections with all-way stop control or traffic signals need the least sight distance.  At all-way stops, drivers need to be able to see vehicles stopped at the other lanes that they are intersecting with.  At signals, drivers approaching the intersections need to see the signal lights.  In jurisdictions that allow right turn on red, drivers in the right lane stop control need the same sight distance as two-way stop control. For example, the driver making the right turn at a red light. Should come to a complete stop and see what other lanes of traffic are doing. If they cannot safely pull into the intersection making the right turn they should stay stopped. These driver’s do not have the right of way.

Although these things are not needed during normal operations, additional sight distance should be provided for signal malfunctions and power outages. For example, when an area that has lost power has traffic signals that are flashing yellow constantly. All ways of traffic should be acting as if it was an all-way stop control. Everyone should be coming to a complete stop and the first people at the stop should have the right of way to safely enter the intersection.

For more details on this manual the website is https://mutcd.fhwa.dot.gov/

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