IIW

Controlling Traffic, Alleviating Congestion

Have you wondered why some intersections have traffic signals, while others do not?

Some think a traffic signal is a cure-all for all traffic problems. While others think a traffic signal would create even more issues.

The Pros, The Cons

Traffic signals provide a maximum degree of control at an intersection. And, if they are installed under the right conditions, a signal can decrease congestion. They also can reduce angle, or broadside, collisions.

On the other end of that, there are many things that should be taken into consideration. Traffic signals can increase rear-end accidents. When unjustified, they can cause excessive delays. A troublesome signal may divert traffic to parallel routes, with drivers taking a residential street to bypass it. This increases traffic on a route that is not designed to handle the higher volume of vehicles, and moves the congestion to another area.

Using Data Before Installing

Before installing traffic signals, you should carefully weigh your options. A traffic study, typically commissioned by the local municipality, is a great way to take a deeper dive into data related to specific intersections. It will tell you how long of a delay motorists experience now versus what the delay will be with a traffic signal, and if the traffic volumes meet the minimum threshold to justify it.

The traffic study may also reveal alternative options, such as a roundabout, a four-way stop, or adding turn lanes.

Guidelines to Follow

Have you wondered why a sign in Iowa looks the same as a sign in California? The Manual on Uniform Traffic Control Devices (MUTCD), issued by the Federal Highway Administration, keeps signs, signals, and pavement markings consistent throughout the United States. It is also the “go to” guide for traffic engineers when designing or installing traffic signals, signage, and pavement markings.

Do you have an intersection that’s congested? Too much traffic? Or, not enough traffic and the traffic signal is slowing things down? I can help. Contact me today at 563-556-2464 or j.vondera@iiwengr.com for more information.

Jeri Vondera, EI is a Design Engineer with 10 years of experience in transportation engineering. She designs traffic control plans, performs traffic impact studies, and models traffic flow using SYNCHRO. She is also very knowledgeable of Iowa DOT Federal-Aid procedures for local public agencies.