by Steve Durian, Transportation and Engineering Director
comments open from May 21 until June 9
Jefferson County’s Transportation and Engineering Division is responsible for evaluating appropriate traffic control alternatives for intersections of roadways and driveways. Typical intersection traffic control used throughout the county includes stop signs, traffic signals, and roundabouts. The county’s traffic engineers consider many factors including traffic volume, crash history, and pedestrian activity when determining the safest and most effective traffic control at intersections.
Stop Signs: Two-way stops are the most common traffic control used at intersections. Two-way stop sign controlled intersections occur where one intersecting roadway or driveway has significantly less traffic than the major street. Multi-way stop signs are used where moderate traffic volumes occur at an intersection and the volume of traffic at all approaches is more balanced.
• The advantages of stop signs is that they are the most efficient method of traffic control for traffic flow where lower traffic volumes are present and they are easier and less expensive to maintain.
• However, when the traffic volume is too great for a stop sign controlled intersection to operate efficiently or crash history indicates that a more controlled measure is needed, traffic engineers look to signalization or roundabouts.
Traffic Signals: Traffic signals become necessary when the delay to traffic would be too great for a stop sign controlled intersection or when a stop sign controlled intersection may cause a significant safety problem. Signalized intersections can vary in size from one travel lane in each direction to multiple lanes with two or more left-turn lanes.
• One advantage of signalizing intersections is that these intersections can operate more efficiently with larger volumes of traffic, especially where left-turning traffic volumes are heavy. Traffic signals can also decrease the incidences of major crashes and can assist pedestrians when crossing wide streets and busy intersections.
• There are several disadvantages to signalized intersections. One disadvantage is the higher operating cost. Another disadvantage is that minor rear-end crashes are more frequent at signalized intersections when compared to other types of intersections. A third disadvantage is that to achieve good traffic flow, signalized intersections cannot be spaced too closely to one another, thereby limiting the number of intersections that can be signalized along a roadway.
Roundabouts: Roundabouts are becoming more common throughout Jefferson County. Intersections controlled by roundabouts can handle higher traffic volumes than stop sign controlled intersections without many of the disadvantages of signalized intersections. Both signalized and stop sign controlled intersections have many conflicting crossing movements which can affect both the safety and efficiency of these types of intersections.
• With a roundabout, there are no left-turns and fewer conflicting or crossing movements resulting in improved traffic flow and decreased potential for severe crashes. Other advantages to roundabouts are that they can help control speeding and they are less costly to operate than signalized intersections.
• A disadvantage to roundabouts is that they require more land area to construct and therefore can be difficult to implement in developed areas where existing improvements limit available space. Roundabouts can also be confusing to drivers who are not accustomed to them or in the case of multi-lane roundabouts with inadequate advanced directional signage.
For more information about traffic safety and operations in Jefferson County, contact the Transportation and Engineering Division at 303-271-8495.