The Cliff and Willow Intersection Project

Mission of the project

WELCOME! The City of Harrisburg is evaluating improvement alternatives to the Cliff and Willow intersection. This website was created to help provide information, and educate the public regarding the future of the intersection at Cliff and Willow. We would like you to participate in the discussion.

We have contracted with Infrastructure Design Group, Inc. (IDG), a local civil engineering consultant that specializes in transportation design, to analyze the traffic impacts in this area and provide alternatives for long term solutions. Currently, two options are being considered: a signalized intersection and a roundabout. Below, we will present information for each of the options being considered. Please note that any information provided here is based on preliminary design, and so specific data presented at this time could change as the design process continues and the design is refined.

Traffic Analysis

Our consultant, IDG, has analyzed the future long term traffic needs for this intersection. We have looked to several courses of traffic data in order to determine our long term needs.

  • We are taking into account the traffic data provided by the Sioux Falls Region Metropolitan Planning Organization’s (MPO) 2045 Long-Range Transportation Plan.

  • We have also applied Lincoln County’s traffic data from their recent 2019 Master Transportation Plan.

  • And the City is also conducting our own traffic analysis of our transportation system, with specific analysis of the traffic impacts of current and future developments.

We have required the design of any improvement here to meet our future traffic needs for at least 25 years into the future. As a result, we have been presented with these layouts for each alternative.



Traffic Capacity

As you can see from the exhibits, the signalized intersection would consist of five to seven lanes of traffic in each direction. And the roundabout is a dual-lane roundabout. The biggest takeaway:

Either of these alternatives will meet our traffic needs for about 25 years.

Please note that expansion beyond our 25-year traffic needs is not feasible in either option due to expected Right-of-Way limitations. After 25 years, the City must ensure that our overall transportation system is adequate in meeting our needs, not just this single intersection.

Transportation System Impact

Either of these alternatives will fit into our current and future transportation system, taking into account traffic patterns and adjacent arterial street intersections. Adjacent intersections are expected to be minimally impacted as a result of constructing either alternative. Please note that either alternative will not and is not intended to provide significant improvements to any adjacent traffic issues. These other traffic issues will be addressed with other future improvements. In fact, the city has already contracted with IDG to define what those corridor improvements would be so we can program those into our Capital Improvement Plan.

That said, a roundabout may be able to better improve overall traffic in the nearby corridors by providing better U-turn type movements at this intersection. Vehicles would simply ride the full 360 degrees of the roundabout and come back in the opposite direction in which they came.

However, in a signalized intersection, if the vehicle is too large to conduct a sharp U-turn, they would need to travel through the intersection and onto the next intersection and then navigate through our local streets to turn around. For example, for those drivers trying to turn left off of Shebal Avenue onto Willow Street may find it faster and safer to simply take a right out and navigate the full 360 degrees of the roundabout at Cliff, resulting in traveling westbound as intended.

Additionally, either alternative will not control future improvement options on our arterial street corridors. For example, if we install a roundabout at Cliff and Willow, we would not be required to install a roundabout at the intersection of Laura and Cliff, nor any other intersection for that matter. Those intersections could be signalized, or also a roundabout.

Level of Service (wait Times)

Harrisburg traffic patterns consist of large peaks in the morning and evenings, as commuters flow to and from work in adjacent communities. Either intersection option is designed to meet a similar level of service. The transportation level of service is defined as a measure of average vehicle delay at the intersection. Basically, how long you may have to wait at the intersection. In either option, the wait is expected to be about the same.

And that holds true for the duration of their lifespans. In 25 years, both intersections will have longer wait times during peak hours due to City growth and increased traffic, but the wait time would still be about the same in either alternative.

However, in a signalized intersection you might find yourself waiting at a red light in an otherwise empty intersection during the majority of non-peak hours of a day. While with the roundabout option, there would be very little delay or red lights to wait for during non-peak hours.


With three schools nearby, we will have many school busses navigating this intersection. Both the signalized intersection and roundabout are designed to allow busses to easily travel through. You may note that busses in the Harrisburg School District already navigate through the roundabouts at Louise and Highway 106 and also 69th St and Southeastern Ave in Sioux Falls. Coincidentally, the roundabout at the 69th and Southeastern is designed to be easily expanded to a dual lane roundabout in the future.


We also have some large truck traffic traveling through these corridors. It’s not a lot, somewhere around less than 5% of the total vehicles. But in any case, both intersection alternatives are designed to allow for trucks to pass through. And our local industries relying on trucking do not frequently include the Cliff and Willow intersection in their trucking routes, nor do they plan to in the future.

Driver SAfety

The intersection, in either alternative, will be designed in accordance with any and all appropriate safety requirements and guidelines. With that said, they are some pretty big differences in crash statistics between a signalized intersection and a roundabout. With the roundabout alternative, the geometry of the roundabout requires the driver to slow down to 20 miles per hour or less. Due to the deflections of the medians, it would be nearly impossible to speed through an intersection or drive distracted for that matter. With a signalized intersection, with a green light, the driver can travel at the speed limit, expected to be 25 mph. The driver could also travel faster than the speed limit if they wanted to beat a red light for instance.

In a small two-lane signalized intersection there are 32 conflict points where vehicle - vehicle crashes could occur. Sixteen of these conflict points are right-angle, or T-bone, type crashes. These are crashes that statistically result in greater injury and damage. While in a single lane roundabout, there are 8 conflict points, none of which are the right-angle type. Statistically installing roundabouts result in significantly less fatal or injury crashes. In application to our alternatives, the dual-lane roundabout is expected to have about 20 potential conflict points (and none right-angle), while the signalized intersection with 5 to 7 lanes in each direction could have 100 or more conflict points (many of which would be the right-angle type).

Pedestrian SAfety

Pedestrians will be able to safely cross the intersection in both alternatives. However, there are some differences in the crossing characteristics that should be considered. The average distance of the pedestrian crossing in the signalized intersection is 5 to 7 lanes, at about 97 feet total, while in a roundabout the average distance to cross is 4 lanes at a total of 44 feet. In the roundabout option, there is also a median that acts as a refuge island. And so, pedestrians only have 22 feet, an island, and another 22 feet to cross. As previously discussed, the roundabout geometry requires the driver to slow down to 20 miles per hour or less. However, with a signalized intersection the driver can travel at the speed limit (25 mph), or even exceed it. Lower speeds are associated with better yielding rates, reduced vehicle stopping distance, and lower risk of collisions. As for conflict points for pedestrians: The dual-lane roundabout is expected to have about 20 potential vehicle-pedestrian conflict points (and none right-angle), while the signalized intersection with 5 to 7 lanes in each direction could have 40 or more vehicle-pedestrian conflict points.

Pedestrians in a roundabout would be provided with pedestrian crosswalk lights at each crossing activated via push button to signal to drivers to stop for that pedestrian. Roundabouts are designed to provide at least one car length outside the roundabout circular path and before the pedestrian crossing so that the vehicle can stop for a pedestrian and also be outside the continuous vehicle movement of the roundabout, allowing for traffic to continue to move in the intersection. Pedestrians with disabilities can also safely cross a roundabout. We would install pedestrian crossing signals that also provide audible alert sounds for those who are visually impaired. There are also push buttons that vibrate to signal a blind-deaf person that the walk sign is on.

Bicycles can also cross a roundabout intersection. However, they would use the pedestrian facilities instead of the roadway.

The Federal Highway Administration Office of Safety identified roundabouts as a Proven Safety Countermeasure because of their ability to substantially reduce the types of crashes that result in injury or loss of life. Roundabouts are designed to improve safety for all users, including pedestrians and bicycles.


Adjacent landowners at this intersection consist of current and future commercial businesses. There are gas station convenience stores at both the southeast and southwest corners of the intersection. And access is extremely important to these businesses.

With a signalized intersection, the median length required is approximately 400 feet on each leg of the intersection to provide for queueing of cars during red light stopping and idling. As a result of these requirements, 6 access points would be reduced to right in and right out only. An estimated 19 businesses would be affected by a signalized intersection. (The pink lines denote the extent of required medians.)

Alternatively, with a roundabout, the median length required is about 150 feet. There is less queueing with a roundabout intersection due to the continuous movement of the intersection. And as a result, 2 access points would be reduced to right in and right out only. An estimated 6 businesses would be impacted by a roundabout. (The blue lines denote the extent of required medians.)

However, with a roundabout, we could have the opportunity to slightly adjust the 2 impacted access points, as shown. This would result in no access points reduced to right in and right out, and no businesses impacted by access. Adjusting access points in the signalized intersection option would not produce any benefits due to the much longer lengths of the medians.

Right Of WAy Needs

With either alternative, the City would need to acquire right of way from at least four landowners in order to construct the improvement.

With the signalized intersection, an estimated

~ 30,200 square feet

of right-of-way acquisition would be necessary.

With the roundabout intersection, an estimated

~ 15,300 square feet

would be necessary.

It should be noted, with any right of way acquisition comes purchase costs. And so, at half the square footage, the roundabout alternative right of way is expected to cost about half as much.


Due to the Cliff and Willow intersection being the current focal point of the city’s transportation system, consideration must be given to the construction process impacts to our residents and visitors.

The signalized intersection:

Construction is expected to take ~ 3 to 6 months. With this alternative there are likely more opportunities for implementing constructing phasing to reduce or nearly eliminate full intersection closure times during construction.

The roundabout intersection:

Construction is expected to take ~ 2 to 3 months. With this alternative, there may be times of two to three weeks of full intersection closure. With the shortened timeframe of the construction, we could potentially construct the entire intersection during summer when school is out of session.


In either scenario, the city will designate detour routes in an effort to mitigate the temporary closures or delays. As with any transportation project, there will be unavoidable impacts to residents during the construction of either alternative.

EStimated Total Project & Life-time costs


Generally speaking, the signalized intersection is much larger than the roundabout option, resulting in an overall much larger price tag. The signalized intersection is about 40,500 square yards of pavement, whereas the roundabout is about 23,000 square yards of pavement. The signalized intersection also requires the signals and associated electric components, which is very expensive. The construction cost for each option are:

  • Signalized intersection is estimated at $3.5 million

  • Roundabout is estimated at $2.0 million


The city has currently secured $2.0 million in funding. This would cover the costs of the roundabout option. If proceeding with the signalized intersection, additional funding would need to be identified and acquired, which could potentially delay project a couple years.

Yearly costs Comparision:

On an ongoing basis, the signalized intersection is expected to cost $6,100 each year for snow removal time and materials, pavement repair and rehabilitation activities, and signal light energy costs. On the other hand, the roundabout option is expected to cost $2,900 each year for operations and maintenance needs.

Lifecycle Costs Comparison:

When comparing improvement alternatives, we often apply an equivalent lift cycle cost analysis, very similar to the methods used by the South Dakota Department of Transportation. The analysis takes into account the annual recurring costs and also replacement cost at the end of the useful life. In this analysis, the signalized intersection has an equivalent lifecycle cost of $88,000, and the roundabout has an equivalent lifecycle cost of $49,900.

Community and Stakeholder Input To-Date

City Staff:

The City has discussed these alternatives first amongst staff.

  • Our Public Works Department has studied the options and is confident that they can maintain either intersection alternative. However, with the roundabout option, there is less pavement to repair, less snow to push, and no signals to maintain, which are all positives from a staff perspective.

  • The City Administration has identified the roundabout alternative as better following the City’s overall planning goals, including the ‘low impact’ environmental goal of our infrastructure systems due to the reduced pavement and energy costs. Also, the roundabout is generally more aesthetically pleasing and provides more landscaping opportunities, which better follows the City’s goal of maintaining that ‘small town feel.’

City of Harrisburg Commissions & Boards:

We have also presented to City Boards including the Planning and Zoning Commission and the Disability Awareness Board. After presenting the information and weighing the pros and cons of each alternative, both of these boards recommended implementing the roundabout option.

Harrisburg School District:

The City has also discussed these alternatives with Harrisburg School District. The School District respects the City’s decision making process to find the best solution possible for their shared tax base and residents following professional engineering recommendations and input from the community.

CHamber and Economic Dev. Board of Directors:

We presented to the Harrisburg Chamber of Commerce/Harrisburg Economic Development Corporation Board of Directors. We had a great discussion on the potential impacts to our business community, and as a result can better share and inform our other business leaders. As development continues along these corridors, staff has shared our alternatives for improving the intersection with these incoming developers in order to best coordinate our growth.

Impacted Landowners:

We have discussed Right of Way acquisition with the 4 adjacent landowners that we will definitely need right of way. As we make our way through this process, conversations with these and potentially other landowners will continue.

Questions? Contact Us!

Thank you for visiting our project page and reviewing the information.

The City will have an open house for public input on the project alternatives on January 12th from 4:30 - 7:30 pm at Liberty Elementary Board Room.

This will be an opportunity where you can come and go at any time during that time period. There will not be a formal presentation, but exhibits of information will be provided and staff will be available to answer any questions you may have. Staff will present a summary of the two design alternatives to the City Council at the January 5h City Council meeting. The city staff will also be hosting an open house, with the same information, on January 12th from 4:30 -7:30 p.m. at the Liberty Elementary school board room. Please feel free to submit your input at any time before then. If you would like to provide any comments or have questions, please contact us at, or you can also contact the City Engineer, Joe Stonesifer, directly at (605) 498-4949.

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