Traffic control: What could be coming downtown

CONTRIBUTED PHOTOS — The Downtown Master Plan will bring about different traffic features such as roundabouts for Marshalltown.

Switching Church and Linn streets from one-way to two-ways will take a little more than a flip of the switch.

The change is what was proposed in the city’s 2019 Downtown Master Plan. In order to make this happen, something else will need to change — traffic control. Particularly, traffic control where the streets intersect with Center Street.

Engineering and consulting firm Bolton and Menk was charged with the task of figuring out how to bring the master plan to fruition with the Downtown Implementation Plan. Among the firm’s many recommendations is the recommendation of changing from traffic lights to circular intersections where Linn and Church meet Center Street.

The reason traffic control needs to change at these intersections is because the traffic signals in place are meant for one-way traffic and can not be used for the conversion to two-way traffic.

Casey Byers, landscape architect for Bolton and Menk, said several options have been considered at these intersections. While evaluating the intersections they discovered traffic demand is low enough for traffic signals to not be warranted. If the city was to put new traffic signals in, improvements to those intersections would not be eligible for state funding because of the traffic signals not being warranted.

On top of that, new traffic signals would be the most expensive way to go, at an equipment cost of about $500,000.

The remaining options are making the intersections four-way stops, or using an alternative intersection such as the circle intersections. The proposed circle intersections would be small; not large roundabouts.

Byers said circle intersections are actually much safer than signaled intersections, despite the perception that they are dangerous or difficult to navigate.

“On a traditional intersection there are something like 32 points of conflict between turning movements and ways vehicles can hit each other and pedestrians,” Byers said. “With circle intersections you reduce that down to eight.”

For pedestrians, a circle intersection shortens the distance for crossing the street where they would be vulnerable to oncoming traffic. Furthermore, these intersections slow vehicles down, lessening the impact if there is an accident between two vehicles or a vehicle and pedestrian.

“When those accidents do happen they tend to be a more low impact collision rather than a head-on or side-swipe collision,” Byers said.

Byers notes there has already been a traffic related death at one of these intersections which often raises a red flag something should change. It also makes the improvements eligible for funding from the Iowa Department of Transportation.

Part of the implementation plan also includes a pavement management plan. The Church and Linn street intersections will already need pavement replacements at some point. Coupling the pavement replacement with the adoption of circle intersections would be another cost-saving opportunity.

Because of the width of the existing intersections, the city would not need to acquire additional land to implement small traffic circles. They would fit within the existing right of way.

“It would provide a gateway feature into downtown. Traffic doesn’t have to stop and you can move traffic through intersections more efficiently,” Byers said.

The short-term downside, according to Byers, is in drivers’ adjusting to the new traffic control method. Michelle Spohnheimer, director of housing and community development, said there would be efforts to educate the public on how to use the traffic circles before they are put in place.

“It’s different if you’re not used to them. The first thing is we would put them in test situations — maybe do some pavement markings or interim kinds of barriers to help direct people and give them an idea how it would work,” she said. “”They work very well at keeping the traffic moving. It’s a good way to introduce some traffic calming in a sense.”

Nothing is set in stone at this point — both Spohnheimer and Byers note — and opportunities for public input and ongoing conversation on the implementation plan will continue to happen.

Spohnheimer said the implementation plan is likely to be presented to the City Council in coming months.

“The council will be looking at that in phases. They (Bolton and Menk) outlined a potential of maybe eight-plus phases of work that could happen,” she said. “Any of those phases could be more than $1 million, maybe up to $5 million depending on the scope. Then the council will budget out what needs to be done first.”

“It won’t happen tomorrow,” she said about circle intersections. “It might be a few years out.”


Contact Joe Fisher at jfisher@timesrepublican.com.


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