Congestion and safety 

at smaller but critical 

intersections using the 

modern roundabout (MRB) 

design principles are 

common problems today. 

The mini-roundabout was 

developed and has been 

deployed at hundreds of 

intersections across the 

United States to address 

such problems!

Small Business Innovation Research

SBIR SuccessSTORY

Mini-Roundabout

June 2022

©2021 ZKxKZ, LLC/Vortex Roundabouts. 

Figure 1. Photograph. Mini-roundabout bird’s eye view.

The Short History of Roundabouts

The history of the roundabout is 

relatively recent and short. Its 

origins are based in Europe at 

the beginning of the 20th century, 

and it has only been implemented 

in the United States since the 

early 1990s. Originally designed 

to be an island for pedestrians, the 

MRB—as it was later coined—has 

proven to have safety and 

economic benefits in its evolution 

of use and design. 

A roundabout is essentially a 

circular intersection. It guides 

drivers in a counterclockwise route 

around a circular center. Drivers 

are forced to slow down and are 

required to yield to vehicles 

already in the roundabout. Modern 

implementations can operate with 

no lighted signals or street signs in 

the roundabout, which helps with 

the continuous flow of traffic. 

However, when traffic demand 

exceeds a variable traffic volume

limit, a signal can be used to 

alternate the right-of-way access. 

Roundabouts are typically installed 

to improve safety and traffic flow 

by forcing vehicles to reduce their 

speed as they approach the 

intersection. Compared with an 

all-way stop-control (AWSC) 

intersection, roundabouts can 

double the capacity to alleviate 

congestion. Because of this

feature, roundabouts are suitable 

for intersections that have a high 

crash rate or overwhelming 

traffic delays.
SBIR SuccessSTORY June 2022 

2 

A Modern Solution to a 

Safety Problem

What are mini-roundabouts, 

and why are they an advantage? 

Mini-roundabouts serve as 

small-scale versions of the MRB

traffic control system that directs 

vehicles circularly through an 

intersection. Regular MRBs have 

nontraversable central islands, 

and their footprint typically 

requires an inscribed circular 

diameter of approximately 100 ft 

or larger. To enable large vehicles 

to pass through the roundabouts, 

truck aprons may be deployed on 

the edge of central islands, on 

shoulder corners, or on both. 

There are also many heavily 

traveled two-lane minor arterial 

roads on which the typical traffic 

control device is either a two-way 

stop-control (TWSC) or AWSC. 

The main problem at TWSC 

intersections is safety: During 

peak hours, vehicles from the 

minor approaches have difficulty 

finding a safe gap to enter the 

intersection. It is even more 

dangerous for pedestrians and 

bicyclists trying to cross a major 

road. At AWSC intersections, 

which are used where two minor 

arterial roads meet, the main 

problem is congestion. Congestion 

at such locations can block 

traffic on many roads, thereby 

feeding traffic to the two minor 

arterial roads.

Frank Blackmore, a U.K. traffic 

engineer who also invented the 

MRB concept, conceived the 

mini-roundabout in 1969. 

Blackmore invented the 

mini-roundabout to solve 

congestion and safety problems 

at smaller, but critical, 

intersections by using the MRB

design principles. In the United 

States, there are currently 

hundreds of mini-roundabouts 

deployed at intersections to 

address these problems. To 

implement the MRB design 

principle at small intersections 

that serve predominately passenger 

cars (with less than 3 percent of 

the traffic being large vehicles),

one logical compromise is to make 

the central island traversable. This 

design allows for occasional use 

by large vehicles that cannot 

navigate tight turns with a small 

radius, while making its edge 

high enough to discourage small 

vehicles from mounting the central 

island. A traversable central 

island is a distinctive feature of 

the mini-roundabout design, 

enabling it to be installed at 

smaller intersections where 

traditional MRBs cannot fit. 

Given the success and benefits 

of mini-roundabouts, the Federal 

Highway Administration (FHWA) 

wanted to investigate whether

there were opportunities to 

improve their design, functionality, 

and processes. With investment 

from FHWA through phase I, II, 

and IIB Small Business Innovation 

Research (SBIR) awards, 

ZKxKZ, LLC, developed a 

design that provides low-cost, 

easily installed mini-roundabouts 

made from recycled plastic. 

This low-cost, recycled 

technology is effective in reducing 

carbon footprints and is 

economically responsible! 

Source: FHWA.

Figure 2. Photograph. Mini-roundabout street-level view.
SBIR SuccessSTORY June 2022

3 

Low-Cost Innovation Using 

Recycled Materials

The conventional methods of 

constructing roundabouts involve 

cutting the pavement and filling it 

with reinforced concrete. However, 

the modular mini-roundabouts that

ZKxKZ developed can be installed 

and anchored directly onto existing 

pavement that is in good condition. 

According to ZKxKZ’s website, 

“An MRB differs from more 

familiar large traffic circles in 

one significant way. Large trucks 

and buses making turns in a 

small-diameter MRB must drive 

over its central circle and splitter 

islands to navigate the turn. 

ZKxKZ has developed a low-cost 

recycled plastic MRB system 

designed to significantly reduce 

the time required for installation. 

The modular components of the 

system allow a damaged section 

to be replaced in minutes with a 

socket wrench.”(1)

ZKxKZ uses a polyethylene-based 

composite to take a completely 

different approach to 

mini-roundabouts—and potentially 

other infrastructure installations

as well. The material, which is 

used for railroad ties, is known to 

be both strong and durable while 

offering the opportunity to design 

and precut pieces for assembly 

at the installation site. Using 

computer-aided design, ZKxKZ 

engineers take measurements from 

a geometric design for an 

installation site and translate them 

into a modular mini-roundabout 

design, which is made up of 

hundreds of parts that fit together 

like a jigsaw puzzle. Using this 

approach, precut boards can be 

delivered onsite, ready to be 

installed. To complete the 

installation, the precut plastic 

boards are lined up on the 

pavement according to the 

plan’s geometric design. The 

installer then drills through each 

piece’s precut holes and into the 

pavement, fills the holes with 

cement, and secures the boards 

by using anchors. This process 

simplifies the labor and, more 

importantly, does not require 

the complete closure of the 

intersection, thereby minimizing 

the effect on the traveling public. 

Federal Funding Fosters New 

Infrastructure Improvements

Through the FHWA’s SBIR award 

investments, ZKxKZ collaborated 

with both Georgia Department of 

Transportation (GDOT) and 

Virginia DOT (VDOT) for initial 

sites in Jackson, GA, and 

Annandale, VA. Because the 

mini-roundabouts are easy to 

install, modify, or remove, these 

sites also provided a convenient 

method for testing and evaluating 

the effects at intersections. For 

example, the Jackson, GA, site 

required postinstallation design 

changes due to the entry speeds 

into the roundabout being deemed 

higher than desired. Small 

modifications to the center islands 

and splitter island shapes were 

implemented to change 

driver behavior. 

The major benefits of these 

recycled plastic mini-roundabouts 

are obvious: They can fit into 

existing intersection rights-of-way, 

they are inexpensive because they 

are smaller, and they use recycled 

material. But the benefits do not 

stop there! As the system has 

undergone development and 

improvement, it has shown its 

potential to be used in other road 

features. ZKxKZ currently has 10 

commercial installations, including 

one site in Silver Spring, MD. 

“[A] low-cost recycled plastic MRB system designed 

to greatly reduce the time required for installation... 

allow a damaged section to be replaced in minutes 

with a socket wrench.” 

—ZKxKZ, LLC
SBIR SuccessSTORY June 2022 

 4 

The system is a spinoff for a 

modular roadway system where 

the road did not have a sidewalk. It 

was adopted for use as a lane 

divider for safety enhancements to 

segregate the lane for pedestrians, 

along with the creation of a bike 

lane. The technology’s simple 

installation techniques and 

adaptable design characteristics 

have made it an effective solution 

with the potential to address a 

variety of other traffic issues as 

development is furthered. 

The success of these installations 

and the potential for other 

future infrastructure-related 

improvements, such as channeling 

curbs and bike lane dividers, led 

FHWA to invest further into the 

development of the system through 

the SBIR phase IIB award. Some 

of those developments include 

load transfer mechanisms to 

distribute vehicle impact loads to 

neighboring boards and anchors. 

To help redistribute impact loads, 

the boards, which are held down 

with anchors, now include dog 

bone-shaped flexible connectors 

to connect the plastic boards. 

When the external plastic boards 

are hit by vehicles, the impact 

force is partially resisted by the 

anchors holding down the boards 

and partially transferred to internal 

boards and their attached anchors 

through the “dog bone” connectors 

to reduce the potential of localized 

material failures. 

This innovative SBIR-funded 

technology has led VDOT to create 

and install more mini-roundabouts 

since the completion of phase II in 

Richmond, VA, with three more 

sites being planned. The success 

of these installations has also led 

to the Department of Defense 

adding $750,000 to the U.S. DOT 

contract for defense-specific 

systems development, furthering 

the SBIR program’s mission to 

help small businesses participate 

in Federal research and 

development, while also fostering 

the commercialization potential 

of this novel technology. 

References 

1. ZKxKZ, LLC. 2022.

“Mini-Roundabouts”

(web page).

http://zkxkz.com/index.php

/mini-roundabouts/, last

accessed May 18, 2022.

HRTM-10/06-22(WEB)E

FHWA-HRT-22-080

https://doi.org/10.21949/1521909

CONTACT: 

TFHRC.webmaster@dot.gov

Source: ZKxKZ, LLC.

Figure 3. Photograph. Mini-roundabout.