133rd Street and 132nd/Hemlock Street

132nd Street and Foster Street

MINI ROUNDABOUTS Overland Park, Kansas September 1, 2017

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TABLE OF CONTENTS

1. INTRODUCTION ................................................................................................... 1 2. LITERATURE REVIEW ......................................................................................... 1 3. CONCEPT ENGINEERING ................................................................................... 4 4. TRAFFIC AND SAFETY ........................................................................................ 7 5. CONCLUSIONS .................................................................................................. 12

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1. INTRODUCTION The City of Overland Park is exploring the concept of mini roundabouts as a low cost, low physical impact intersection solution while still achieving the operational and safety benefits of a modern roundabout. This project includes the study of new mini roundabouts at two existing stop-controlled intersections of 133rd Street and 132nd Street/Hemlock as well as 132nd Street and Foster Street. This study performs the following tasks:

• Literature review • Concept engineering • Traffic and safety • Conclusions

2. LITERATURE REVIEW 2.1 Research and Publications The concept of a mini roundabout came from the United Kingdom. The mini roundabout is ideal for areas requiring a small footprint. The traffic characteristics ideal for a mini roundabout are an average daily traffic (ADT) of 15,000 or less, less than three percent truck volume and approach speeds of less than 35 MPH. Mini roundabouts can be considered for four-way intersections that have not met signal warrant requirements. The challenge with mini roundabouts compared to modern sized roundabouts is ensuring that drivers see them. Modern roundabouts have signs and raised landscaping in the center island that draws the driver’s attention. The central island of a mini roundabout has a low profile to allow for large trucks and buses to drive onto it. Considerations to keep in mind when designing a mini roundabout include:

• Lighting surrounding the intersection • Pedestrian crosswalk back minimum one car length of intersection • Slope of center island

Table 1 provides additional mini roundabout characteristics compared to a modern roundabout.

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Table 1: Mini Roundabout Characteristics

Category Modern Roundabout1 Mini Roundabout Inscribed Diameter 90’ – 150’ 45’ – 90’ Island Diameter 58’ – 110’ 13’ – 58’ Approach Speed 25 – 45 MPH <35 MPH Maximum Speed 25 MPH 15 MPH Capacity (ADT) 17,000 15,000 Signage On approach and on island On approach

Curb Height Varies. Traditionally has curb separation

Varies. Traditionally domed. 5% – 6% cross slope

Pedestrian/Bike Yes Yes Construction Cost Range $200,000 - $500,000 $25,000 - $400,000 Construction Median Cost $250,000 $125,000

Source: FHWA, TRB and personal interviews from two counties that have implemented mini roundabouts. 1 Assumes single lane roundabout Because modern roundabouts are larger there is a greater likelihood of additional costs of utilities, grading, center island landscaping and right of way. These costs can vary widely and can increase the modern roundabout total cost by an additional $1.5M to $2M depending on the number of travel lanes. 2.2 Peer Feedback Interviews were conducted with representatives from King County, Washington and Harford County, Maryland regarding mini roundabouts that they recently installed. Table 2 below shows the seven questions asked and their responses.

Table 2 Peer Feedback

Question King County, WA Harford County, MD

1. Why did you decided to build a mini roundabout?

To improve safety and get speeds down approaching the intersection

Safety concerns. Existing utility relocation was expensive.

2. What problems did the mini roundabout solve?

Got the speed down to 15-18 MPH. Congestion was reduced. Safety improved.

Issues of safety and traffic volumes. Pedestrians having issues getting around. Safer than

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traditional roundabouts.

3. What do you think of the mini roundabout since its been built?

They think that it is a wonderful tool.

The mini roundabout should be reserved for special cases where there is minimal right-of-way

4. What does the public think of the mini roundabout since its been built?

Haven’t gotten any public opposition. 100% crash reduction in White Center, 11 years and counting! Pedestrians feel almost too comfortable and sometimes cut through circle.

In the county, they’ve had quite a few roundabouts already. It really wasn’t too much of an issue for people to see a mini roundabout.

5. Do you plan to build more mini roundabouts?

Yes, building some right now.

Yes. 2 being built.

6. What did you save by building the mini roundabout? (e.g. capital dollars, ROW, time, etc.)

Quantified on a case by case basis. Typically, single lane roundabouts are built for $400-600k. Newest estimates for a mini roundabout are approximately $150k. But you could probably do them for $50-100k if you wanted.

This one was close to $100,000. You could probably get away with doing one cheaper than what they did.

7. How has the safety and traffic operations changed since you built the mini roundabout?

Crash reduction of 100% over the last 5 years!

With all the roundabouts, there are fewer accidents. Chance of fatality goes down significantly.

Source: Interviews were conducted for Harford County on August 18, 2017 and for King County on August 16, 2017

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Both counties provided positive comments regarding their experience with mini roundabouts. The operations and safety benefits were substantially positive for both counties. Both counties noted that the traffic queuing that was once a problem has all but gone away. The cost of a mini roundabout is far less than a traditional roundabout. As far as the public’s reaction, both counties have noted a positive experience among drivers after they drove through the intersection. Both counties have more mini roundabouts being planned and constructed. 3. CONCEPT ENGINEERING High level concept engineering was performed at the study intersections to better understand the mini roundabout design elements. 3.1 Mini Roundabout Design Elements Figures 1 and 2 shows how a mini roundabout would be incorporated into the two study intersections. Some of the key design elements are the roundabout fitting in the existing intersection, mountable center island, and mountable splitter islands.

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Figure 1: 133rd Street and 132nd Street/Hemlock Mini Roundabout Concept

The mini roundabout concept at 132nd Street/133rd Street/Hemlock utilizes a 100’ inscribed diameter, which is larger than the prescribed mini roundabout range, to fit the footprint of the existing intersection. The sidewalks and trails have been realigned to obtain a min. of 20’ from the entry where possible while staying within existing ROW. The left turn lanes have been removed on all legs allowing for a small splitter island. The central island is constructed of brick pavers with a mountable median for larger trucks and buses. The approximate construction cost to convert the 4-way stop intersection to a mini roundabout in the above configuration is $180,000 (2017 Dollars).

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Figure 2: 132nd Street and Foster Street Mini Roundabout Concept

The mini roundabout concept at 132nd Street/Foster Street utilizes a 70’ inscribed diameter to fit the footprint of the existing intersection. The sidewalks and trails have been realigned to obtain a min. of 20’ from the entry where possible while staying within existing ROW. The left turn lanes have been removed on all legs allowing for a small splitter island. The central island is constructed of brick pavers with a mountable median for larger trucks and buses. The approximate construction cost to convert the intersection to a mini roundabout in the above configuration is $80,000 (2017 Dollars). 3.2 Mini Roundabouts vs. Modern Roundabout Trade-Offs The main geometric distinctions between a mini roundabout and a modern single lane roundabout are the inscribed diameter and central island. The smaller inscribed diameter leads to a lower circulating speed and a lower capacity of 15,000 ADT (FHWA Technical Summary on Mini-Roundabouts) vs. 17,000 (NCHRP Report 672 - Roundabouts: An Information Guide) ADT for a modern roundabout. The mountable central island results

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in lower visibility of the roundabout resulting in use on lower speed roadways of 35mph vs. 45mph roadways for modern roundabouts. 4. TRAFFIC AND SAFETY A traffic analysis was conducted at the study intersections of 132nd Street/133rd Street/Hemlock and 132nd Street/Foster Street to evaluate the operational performance and level of service (LOS) of these intersections. Existing LOS for AM and PM peak hours were measured using a calibrated Synchro/SimTraffic model (version 9) based upon methodologies presented in the Highway Capacity Manual (HCM), Sixth Edition. For the mini roundabout analysis, an uncalibrated VISSIM model (version 9) was used. 4.1 Existing Conditions Existing traffic volumes from August 2017 were collected by the City of Overland Park and used to determine intersection LOS for the following identified peak hours.

• AM Peak Hour (7:30 – 8:30 AM) • PM Peak Hour (4:35 – 5:35 PM)

Both existing intersections evaluated are unsignalized (stop controlled), thus overall intersection LOS is determined by the worst turn movement. Table 3 provides the intersection LOS for AM and PM peak hours under existing conditions.

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Table 3: Existing Intersection Level of Service

Source: Synchro ver. 9

Results from Table 3 show that both intersections evaluated experience an unacceptable LOS with delays over 80 seconds per motorist. At Hemlock, the northbound and eastbound movements experience significant delays in the AM and the westbound movements experience the most delay in the PM. At Foster, the southbound movement experiences the most delay in the AM and PM. 4.2 Existing plus Apartments Conditions An Existing Plus Apartments traffic analysis was performed by using existing traffic volumes and projected generated trips because of a proposed residential development at the south end of 132nd Street/Foster Street. The no-build analysis assumes the City of Overland Park doesn’t implement the mini-roundabouts and maintains the existing road configuration. Table 4 provides the overall intersection LOS for AM and PM peak hours for future traffic volumes along the existing intersection stop control.

Intersection Stop ControlAM Number of

VehiclesAM LOS

(veh./sec)AM Overall

LOSPM Number of

VehiclesPM LOS

(veh./sec)PM Overall

LOS

132nd Street/133rd Street/Hemlock Southbound Left 186 B (13.6) 120 B (10)Southbound Thru 56 A (9.4) 80 B (11.8)Southbound Right 8 A (7.5) 10 B (11)Northbound Left 28 F (66.8) 69 B (13.2)Northbound Thru 56 F (>120) 154 C (19.6)Northbound Right 438 F (>120) 75 B (14.8)Eastbound Left 3 F (94.8) 11 B (11.1)Eastbound Thru 373 F (>120) 109 B (12.9)Eastbound Right 26 F (>120) 42 B (12)Westbound Left 21 A (5.5) 205 E (48.2)Westbound Thru 48 A (5.9) 229 F (88.8)Westbound Right 30 A (5.1) 248 F (85)ALL 1273 F (>120) 1352 E (45.3)132nd Street/Foster StreetEastbound Left 627 A (8.8) 94 B (12.8)Eastbound Thru 457 A (1.6) 271 A (0.7)Eastbound Right 0 A (0) 0 A (0)Westbound Left 0 A (0) 0 A (0)Westbound Thru 62 A (1.9) 503 A (2.6)Westbound Right 106 A (1.7) 19 A (1.8)Northbound Left 0 A (0) 0 A (0)Northbound Thru 0 A (0) 0 A (0)Northbound Right 0 A (0) 0 A (0)Southbound Left 6 F (>120) 92 F (>120)Southbound Thru 0 A (0) 0 A (0)Southbound Right 35 A (2.6) 378 E (66.4)ALL 1293 A (6.2) 1357 C (31.3)

Unsignalized

Unsignalized

F (>120)

F (>120)

F (88.8)

F (>120)

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Table 4: Existing Plus Apartments Intersection Level of Service

Source: Synchro ver. 9 Results from Table 4 paint a similar picture to the existing traffic scenario, with both intersections experiencing an unacceptable LOS, achieving delays over 80 seconds per motorist. Much like under existing conditions, the northbound and eastbound movements at Hemlock experience significant delays in the AM and the westbound movements experience the most delay in the PM. At Foster, the southbound movement experiences the most delay in the AM and PM.

4.3 Existing with Mini Roundabouts Table 5 shows the results for the existing conditions with mini roundabouts alternative.

Intersection Stop ControlAM Number of

Vehicles AM LOS

(veh./sec)AM Overall

LOSPM Number of Vehicles

PM LOS (veh./sec)

PM Overall LOS

132nd Street/133rd Street/Hemlock Southbound Left 189 C (15.5) 136 A (9.9)Southbound Thru 56 A (9.3) 80 B (13.2)Southbound Right 8 A (7.7) 10 B (10.4)Northbound Left 28 F (92) 69 B (12.5)Northbound Thru 56 F (>120) 154 C (20.5)Northbound Right 447 F (>120) 113 C (16.6)Eastbound Left 3 F (>120) 11 B (12.6)Eastbound Thru 376 F (>120) 125 B (13.7)Eastbound Right 26 F (>120) 42 B (13.4)Westbound Left 51 A (6.5) 220 F (59.2)Westbound Thru 63 A (6.8) 244 F (101.1)Westbound Right 37 A (5.3) 258 F (97.7)ALL 1340 F (>120) 1462 F (50.9)132nd Street/Foster StreetEastbound Left 627 A (9.1) 94 A (8.4)Eastbound Thru 457 A (1.5) 271 A (1.3)Eastbound Right 15 A (1.5) 70 A (0.9)Westbound Left 28 A (6.4) 54 A (5.1)Westbound Thru 62 A (2.2) 503 A (2.4)Westbound Right 106 A (1.9) 19 A (1.9)Northbound Left 52 F (>120) 40 D (41.3)Northbound Thru 30 F (>120) 10 E (57.5)Northbound Right 66 F (>120) 50 B (16)Southbound Left 6 F (>120) 92 F (>120)Southbound Thru 18 F (>120) 31 F (>120)Southbound Right 35 F (>120) 378 F (>120)ALL 1502 F (89.5) 1612 E (62.1)

Unsignalized F (>120) F (>120)

Unsignalized F (>120) F (101.1)

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Table 5: Existing Mini Roundabout Intersection Level of Service

Source: VISSIM ver. 9 In the AM, Hemlock Street at West 133rd/132nd Street performs at a LOS F. Vehicles travelling northbound on Hemlock are queuing because vehicles travelling eastbound on 133rd are preventing them from entering the mini roundabout. The queuing does clear during the model simulation. The two mini roundabouts in the PM perform at a reasonable LOS. Table 6 shows the results for the mini roundabouts plus apartments alternative.

Intersection Stop ControlAM Number of

VehiclesAM LOS

(veh./sec)AM Overall

LOSPM Number of

VehiclesPM LOS

(veh./sec)PM Overall

LOS

132nd Street/133rd Street/Hemlock Southbound Left 186 A (5.4) 120 A (8.4)Southbound Thru 56 A (7) 80 B (10.9)Southbound Right 8 B (10.9) 10 A (9.7)Northbound Left 28 F (>120) 69 A (5.1)Northbound Thru 56 F (>120) 154 A (4.5)Northbound Right 438 F (>120) 75 A (3.7)Eastbound Left 3 A (3.1) 11 A (6.1)Eastbound Thru 373 A (2.5) 109 A (6.6)Eastbound Right 26 A (2.5) 42 A (6.3)Westbound Left 21 A (1.9) 205 B (13.9)Westbound Thru 48 A (1) 229 B (13.6)Westbound Right 30 A (1.1) 248 B (12.9)ALL 1273 F (67.5) 1352 A (9.7)132nd Street/Foster StreetEastbound Left 627 D (31.7) 94 A (2.3)Eastbound Thru 457 D (31.3) 271 A (2.8)Eastbound Right 0 A (0) 0 A (0)Westbound Left 0 A (0) 0 A (0)Westbound Thru 62 B (13.5) 503 A (5.5)Westbound Right 106 B (14) 19 A (3.6)Northbound Left 0 A (0) 0 A (0)Northbound Thru 0 A (0) 0 A (0)Northbound Right 0 A (0) 0 A (0)Southbound Left 6 A (1.6) 92 E (36.8)Southbound Thru 0 A (0) 0 A (0)Southbound Right 35 A (0.8) 378 E (35.3)ALL 1293 D (28.2) 1357 C (15.3)

Roundabout F (67.5) A (9.7)

Roundabout D (28.2) C (15.3)

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Table 6: Existing Mini Roundabout Apartments Intersection Level of Service

Source: VISSIM ver. 9 When the southern leg of Foster Road is added to the mini roundabout, the LOS deteriorates, especially in the AM. The high volume of traffic travelling eastbound on 132nd street prevents vehicles from entering the mini roundabouts from the northbound direction at both intersections. In the PM, the queuing takes place in the southbound direction at Foster Road, contributing to the LOS E at that intersection. Table 7 shows the crash data for both study intersections from 2014 to 2016. Eleven total accidents were reported between both intersections with one of them sustaining injuries. Based on research, a roundabout may bring the number and severity of the crashes down as compared to the existing stop controlled conditions.

Intersection Stop ControlAM Number of

Vehicles AM LOS

(veh./sec)AM Overall

LOSPM Number of Vehicles

PM LOS (veh./sec)

PM Overall LOS

132nd Street/133rd Street/Hemlock Southbound Left 189 A (3.4) 136 B (13.9)Southbound Thru 56 A (2.4) 80 B (13.3)Southbound Right 8 A (3.1) 10 B (12.9)Northbound Left 28 F (>120) 69 A (6.3)Northbound Thru 56 F (>120) 154 A (5.6)Northbound Right 447 F (>120) 113 A (5.1)Eastbound Left 3 A (9.5) 11 B (10.6)Eastbound Thru 376 A (7.8) 125 A (7.9)Eastbound Right 26 A (6.9) 42 A (6.9)Westbound Left 51 A (1.6) 220 C (18.7)Westbound Thru 63 A (1.3) 244 C (18.5)Westbound Right 37 A (1.2) 258 C (17.7)ALL 1340 F (81.3) 1462 B (13.1)132nd Street/Foster StreetEastbound Left 627 F (56.4) 94 A (3.5)Eastbound Thru 457 F (55.8) 271 A (4.3)Eastbound Right 15 F (58) 70 A (3.8)Westbound Left 28 C (16.5) 54 A (7.2)Westbound Thru 62 C (18.9) 503 A (7.3)Westbound Right 106 C (16.9) 19 A (5.1)Northbound Left 52 F (>120) 40 A (8.2)Northbound Thru 30 F (>120) 10 A (8.6)Northbound Right 66 F (>120) 50 A (5.9)Southbound Left 6 A (2) 92 F (>120)Southbound Thru 18 A (1.7) 31 F (>120)Southbound Right 35 A (0.9) 378 F (>120)ALL 1502 F (>120) 1612 E (42.1)

Roundabout F (81.3) B (13.1)

Roundabout F (>120) E (42.1)

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Table 7: Crashes between January 1, 2014 through December 31, 2016

Intersection Total Accidents

Accident Type Injury

132nd/133rd and Hemlock 7 5 - Angle and 2 - Rear End 0 132nd and Foster 4 1 - Head On and 3 - Rear End 1

Source: OP Crash Data 5. CONCLUSIONS The City of Overland Park is exploring the concept of mini roundabouts as a low cost, low physical impact intersection solution while still achieving the operational and safety benefits of a modern roundabout. The following section provides the conclusions and recommendations from the study.

• Literature review o Roundabouts provide a safe and efficient option compared to stop

controlled intersections. o Mini roundabouts are generally less expensive than a modern roundabout

or a traffic signal. Much of the cost differential between a mini roundabout and modern roundabout is the amount of right of way and utility impacts.

o Based on two per reviews, mini roundabouts were primarily used for safety and cost benefits.

• Concept engineering

o Mini roundabouts can be implemented at the two study intersections with no ROW and utility impacts. The mini roundabout can be constructed with only changes to the median and adding the central island.

• Traffic analysis and safety

o Table 8 shows the AM, PM and ADT of the two study intersections as well

as the two peer review intersections. As discussed above, the capacity of a mini roundabout is estimated to be around 15,000 vehicles per day. Both study intersections are currently approaching this capacity.

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Table 8 Existing Traffic Comparison

Intersection Intersection Type AM PM ADT1

133rd and 132nd Street/Hemlock 4-Way Stop 1,273 1,352 13,520

133rd and Foster 2-Way Stop 1,293 1,357 13,570 King County, WA Mini Roundabout ~100 ~100 ~1,000

Harford County, MD Mini Roundabout 679 1,158 11,741 1 ADT for the two OP intersections was estimated using a 10% k factor.

o Both intersections currently operate at LOS F in the AM and PM peak hours as stop controlled intersections.

o When both study intersection are modeled with mini roundabouts with existing traffic volumes (and a new south leg at 133rd and Foster), LOS problems still exist but to a lesser extent than the existing stop controlled intersections.

In conclusion, the mini roundabout does provide safety benefits over the existing stop controlled intersections and cost benefits over the modern roundabout. However, some movements are expected to have operational problems with existing traffic demand that may get worse with future traffic demand. Recommendations from the study include:

• Understand future traffic demand • Analyze a mini roundabout with a bypass lane to improve traffic operations while

minimizing right of way and utility impacts • Analyze a modern roundabout with increased capacity • Perform a traffic signal warrant • Mini roundabouts provide many benefits and are increasingly growing in

popularity around the country. The City may still want to consider mini roundabouts as a good solution in other locations.