Final Report

# 

**STATE-OF-THE-ART REPORT ON:**

ROUNDABOUTS DESIGN, MODELING

AND SIMULATION

Dr. Mohamed A. Aty, PE

Department of Civil & Environmental Engineering

University of Central Florida

Orlando, FL 32816

407-823-5657, Fax: 407-823-3315

<mabdel@mail.ucf.edu>

and

Dr. Yasser Hosni, PE

Department of Industrial Engineering

University of Central Florida

March 2001

# Executive Summary

With the increased success of roundabout use in Europe and Australia,
there is a renewed interest of their use in the US. Several States,
including Florida, are now considering the use of roundabouts to solve
traffic problems. A large number of diverse factors are involved in
designing a roundabout. Interactions between analytical, statistical,
geometrical, static, as well as dynamic traffic factors make the design
of roundabouts a difficult problem. There are design guidelines, however
there are no formal studies to assess the effectiveness use of
roundabout in the US. On the other hand, when interactions between
design factors are so complex, simulation techniques are used to support
the design function.

This research investigated the state-of-the-art in roundabout design and
analysis. The research team also investigated the use of a computer
based simulation package for the design and analysis of roundabouts in
the US. The Visual Simulation Environment (VSE) simulation tool was
acquired and tested. Numerous traffic factors, and standards were found
to be important in the simulation model. Three main criteria should be
considered: safety, delays, and capacity. These criteria can be used to
study the feasibility of using roundabouts, determine optimum design
parameters, compare traffic scenarios, or compare a roundabout to an
intersection, among other design functions. Our research pointed also to
the significance of driver behavior. An essential element in the
simulation of roundabouts is the gap acceptance process, as gap
acceptance at roundabouts is likely to be different from traditional gap
and lag times used for acceptance and rejections.

Although several computer programs such as SICRA, ARCADY and RODEL were
identified, there is a need for simulation models that are more tailored
to the US characteristics. All these programs are developed and
validated in Europe or Australia, except the HCM software. As pointed
above, roundabout analysis is dependent on gap acceptance and drivers'
behavior, therefore there is a need for a US-based simulation model that
takes into consideration US driving conditions and drivers' behavior. As
more roundabouts are built in the US, data will become available to
validate a US model.

**TABLE OF CONTENTS**

Executive Summary

List of figures

List of tables

Introduction [1](#introduction)

GEOMETRIC DESIGN ELEMENTS [7](#geometric-design-elements)

Inscribed Circle [9](#inscribed-circle)

Circulatory Roadway [9](#circulatory-roadway)

Central Island [9](#central-island)

Truck Apron [9](#truck-apron)

Splitter Island [10](#splitter-island)

Bypass Lane [10](#bypass-lane)

Pedestrian Crossing [10](#pedestrian-crossing)

Approach Width [10](#approach-width)

Departure Width [10](#departure-width)

Entry Width [10](#entry-width)

Exit Width [11](#exit-width)

Flare [11](#flare)

Entry Angle [11](#entry-angle)

Entry Radius [11](#entry-radius)

Exit Radius [11](#exit-radius)

Traffic operations [12](#traffic-operations)

Capacity [12](#capacity)

Empirical (British) Method [13](#empirical-british-method)

Analytical (Australian) Method [14](#analytical-australian-method)

Comparison between Roundabout Capacity Models
[14](#comparison-between-roundabout-capacity-models)

Delay [16](#delay)

Safety [17](#safety)

Advantages of Roundabouts [19](#advantages-of-roundabouts)

Less Serious Accidents [19](#less-serious-accidents)

Construction, Operating, and Maintenance Costs
[20](#construction-operating-and-maintenance-costs)

Self Regulating [20](#self-regulating)

Environmental benefits [21](#environmental-benefits)

Disadvantages of Roundabouts [21](#disadvantages-of-roundabouts)

Flat Area [21](#flat-area)

Signal Coordination [21](#signal-coordination)

Unbalanced Flow [22](#unbalanced-flow)

Pedestrians / Bicyclists Safety [22](#pedestrians-bicyclists-safety)

MODELING AND SIMULATION [22](#modeling-and-simulation)

Compute Programs [23](#compute-programs)

SIDRA [24](#sidra)

RODEL [26](#rodel)

ARCADY [26](#arcady)

KREISEL [27](#kreisel)

GIRABASE [27](#girabase)

HCM Software [27](#hcm-software)

summary and conclusions [28](#summary-and-conclusions)

biblography [30](#biblography)

Appendix [31](#appendix)

#  

# List of figures

Figure 1 : Traffic circles "A" and modern roundabouts "B"
[2](#__RefHeading___Toc509223504)

Figure 2. Basic geometric elements of roundabout (FL roundabout design
guide, 1996) [4](#__RefHeading___Toc509223505)

Figure 3. Geometric factors of roundabout approach (Bared *et al*, 1997)
[4](#__RefHeading___Toc509223506)

Figure 4. Minimum configuration for a simple roundabout
[5](#__RefHeading___Toc509223507)

Figure 5. Design elements of roundabouts (Bared *et al*, 1997)
[8](#__RefHeading___Toc509223508)

Figure 6. Entry capacity and circulating flow parameters (Polus and
Shmueli, 1997) [12](#__RefHeading___Toc509223509)

Figure 7. International comparison of entry capacities for single-lane
roundabouts [15](#__RefHeading___Toc509223510)

Figure 8. Roundabout with right-turn bypass lane
[16](#__RefHeading___Toc509223511)

Figure 9. Average delay versus reserve capacity (Brilon and Vandehey,
1998) [17](#__RefHeading___Toc509223512)

Figure 10. Potential conflict points between an intersection and a
roundabout [18](#__RefHeading___Toc509223513)

Figure 11. Examples for accident models for roundabout and signalized
intersections [19](#__RefHeading___Toc509223514)

# List of tables

Table 1. Design Elements Stated by Three Guidelines (Bared *et al*,
1997) [6](#__RefHeading___Toc509223603)

Table 2. Entry Capacity Equations for Roundabouts (Brilon and Vandehey,
1998) [15](#__RefHeading___Toc509223604)

# Introduction

The modern roundabout is a type of circular intersection that has been
successfully implemented in Europe and Australia over the past few
decades. Despite the approximately 35,000 roundabouts in operation
around the world, there are fewer than 50 that exist in the United
States. Until recently, roundabouts have been slow to gain support in
the US. The lack of acceptance can generally be attributed to the
negative experience with traffic circles or rotaries built in the
earlier half of the twentieth century. Severe safety and operational
problems caused these traffic circles to fall out of favor by the
1950\'s. However, substantial progress has been achieved in the
subsequent design of circular intersections.

Modern roundabout should not be confused with the traffic circles of the
past. Modern roundabout have been used successfully in many cities
throughout the world, including several in the US. They have recently
been built in California, Colorado, Florida, Maryland, Nevada, and
Vermont. Two states, Florida and Maryland, have published guidelines for
the design and justification of modern roundabouts. Modern roundabouts
(Figure 1) are distinguished from traffic circles by

1.  Roundabouts follow the \"yield-at-entry\" rule in which approaching
    vehicles must wait for a gap in the circulating flow before entering
    the circle, whereas traffic circles require circulating vehicles to
    grant the right of way to entering vehicles.

```{=html}
<!-- -->
```
1.  Roundabouts involve low speeds for entering and circulating traffic,
    as governed by small diameters and deflected entrances. In contrast,
    traffic circles emphasize high-speed merging and weaving, made
    possible by larger diameters and tangential entrances.

2.  Parking is not allowed on the circulating roadway

3.  No pedestrian activities take place on the central island.

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  ![](media/image1.wmf){width="2.911111111111111in"
  height="2.113888888888889in"}

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[]{#__RefHeading___Toc509223504 .anchor}Figure 1 : Traffic circles "A"
and modern roundabouts "B"

> (Public Roads, Autumn 1995)

There are a large number of factors that should be considered in the
design of the roundabout. In the preliminary study for this project, the
following were identified as factors affecting the design and
performance of the roundabout. Dimensional/ geometric factors affecting
roundabout operations:

-   Number of legs

-   Roundabout diameter (D)

-   Entry radius (r)

-   Flare length (*l'*)

-   Entry width (*e*)

-   Approach width (*v*)

-   Entry angle (**)

-   Number of lanes

-   Separator island and its design

The aforementioned dimensions are illustrated in Figures 2, 3 and 4.

Traffic flow factors include:

-   Entering flow (ADT or pcu/hr)

```{=html}
<!-- -->
```
-   Circulating flow (ADT or pcu/hr)

-   Design speed

-   Traffic mix

Other factors which would affect the design of the roundabout include:

-   Location (urban, suburban, or rural)

-   Traffic standards

-   Traffic rules

-   Lighting

Combinations of these factors, and any other factors affect the
performance of a roundabout. Because of the infinite number of
combinations, countries have developed guidelines for roundabout design.

British, French and Australian guidelines are shown in Table 1.

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[]{#__RefHeading___Toc509223505 .anchor}Figure 2. Basic geometric
elements of roundabout (FL roundabout design guide, 1996)

  -----------------------------------------------------------------------
  ![](media/image3.jpeg){width="2.4402777777777778in"
  height="2.473611111111111in"}

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[]{#__RefHeading___Toc509223506 .anchor}Figure 3. Geometric factors of
roundabout approach (Bared *et al*, 1997)

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  ![](media/image4.jpeg){width="5.995833333333334in"
  height="7.232638888888889in"}

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[]{#__RefHeading___Toc509223507 .anchor}Figure 4. Minimum configuration
for a simple roundabout

> (FL roundabout design guide, 1996)

[]{#__RefHeading___Toc509223603 .anchor}Table 1. Design Elements Stated
by Three Guidelines (Bared *et al*, 1997)

+---------------------+---------------+--------------+----------------+
| DESCRIPTION         | BRITISH       | AUSTRALIAN   | FRENCH         |
+---------------------+---------------+--------------+----------------+
| Central Island      | Min. 4m       | Min. 5m,     | Min. 7m        |
| diameter (at the    |               |              |                |
| non-mountable       |               | Recommend    |                |
| curbs)              |               | 10m          |                |
|                     |               |              |                |
|                     |               | Typical      |                |
|                     |               | 20-30m       |                |
+---------------------+---------------+--------------+----------------+
| Width of            | Max. 15m      | \            | Min. 6.5 -     |
| circulatory         |               | -\-\-\-\-\-\ | 8.5m           |
| travel-way (curb to |               | -\-\-\-\-\-\ |                |
| curb)               |               | -\-\-\-\-\-- | Max. 9m        |
+---------------------+---------------+--------------+----------------+
| Inscribed circle    | Min. 15m      | \            | \-\-\-\-\      |
| diameter            |               | -\-\-\-\-\-\ | -\-\-\-\-\-\-\ |
|                     | Max. 100m     | -\-\-\-\-\-\ | -\-\-\-\-\-\-- |
|                     |               | -\-\-\-\-\-- |                |
+---------------------+---------------+--------------+----------------+
| Cross-Section       | Adverse and   | Adverse      | Adverse        |
| (X-tion) of         | crowded       | X-section    | X-section      |
| circulatory         | X-tion        | Min. 2.5 -   | recommend 1-2% |
| travel-way          | recommend     | 3%           |                |
|                     | 2-2.5%        |              |                |
+---------------------+---------------+--------------+----------------+
| Entry width (Curb   | Min. 4m       | Min. 5m      | Recommend      |
| to Curb)            |               |              |                |
|                     | Max. 15m      |              | 5m for 1-In    |
|                     |               |              | approach       |
|                     |               |              |                |
|                     |               |              | 8m for 2-In    |
|                     |               |              | approach       |
+---------------------+---------------+--------------+----------------+
| Entry Radius        | Min. 6m       | \            | Recommend      |
|                     |               | -\-\-\-\-\-\ | 10-15m entry   |
|                     | Recommend 20m | -\-\-\-\-\-\ | radius\<=      |
|                     |               | -\-\-\-\-\-- | inscribed      |
|                     |               |              | radius         |
+---------------------+---------------+--------------+----------------+
| Exit width (curb to | Recommend     | Min. 5m      | Recommend 5-6m |
| curb)               | 7-7.5m        |              | for 1-In, 8m   |
|                     |               |              | for 2-In       |
+---------------------+---------------+--------------+----------------+
| Exit Radius         | Min.20m,      | \            | Min. 15m, Max. |
|                     |               | -\-\-\-\-\-\ | 30m            |
|                     | desirable 40m | -\-\-\-\-\-\ |                |
|                     |               | -\-\-\-\-\-- | Exit rad. \>   |
|                     |               |              | central Isl.   |
|                     |               |              | radius         |
+---------------------+---------------+--------------+----------------+
| Length of separator | 20-50m        | Comfortable  | = to radius of |
| island              |               | deceleration | inscribed      |
|                     |               | length (high | circle         |
|                     |               | speed)       |                |
+---------------------+---------------+--------------+----------------+
| Lighting            | Required      | Required     | 1.  Required   |
|                     |               |              |     if         |
|                     |               |              |     approach   |
|                     |               |              |     is already |
|                     |               |              |     lighted    |
|                     |               |              |                |
|                     |               |              | 2.  Otherwise  |
|                     |               |              |     not        |
|                     |               |              |     required   |
|                     |               |              |     in rural   |
|                     |               |              |     areas      |
+---------------------+---------------+--------------+----------------+

While the guidelines are useful, the diversity in the values between
countries, and within each factor, as well as the fuzziness of the terms
used limit its use only as guidelines. In addition the guidelines are
particular to specific country, and it is not inclusive to all factors.

There is a need for an efficient tool that would enable traffic analysts
to evaluate different combinations of design and traffic factors and
propose efficient designs in a timely manner. When interactions between
design factors are so complex, such as the case of roundabout design;
simulation techniques proved to be the most efficient tools to support
the design function.

# GEOMETRIC DESIGN ELEMENTS 

There is no uniform design guidance in the U.S. for modern roundabouts.
However, the Federal Highway Administration is planning to develop
guidelines, and information on roundabouts will also be introduced in
the next edition of AASHTO\'s Policy on Geometric Design of Highways and
Streets. The design practices currently used in the US are generally
based on either the British or the Australian guidelines.

The basic principle of roundabout design is to restrict the operating
speed within the intersection by deflecting the paths of entering and
circulating vehicles. Safety and capacity benefits can be fully achieved
only if vehicles are physically unable to traverse the roundabout at
speeds higher than approximately 40 km/h. The major elements of a
![](media/image5.png){width="6.055511811023622in"
height="6.555511811023622in"}roundabout are shown in Figure 5. 5and are
described as follows:

[]{#__RefHeading___Toc509223508 .anchor}Figure 5. Design elements of
roundabouts (Bared *et al*, 1997)

## Inscribed Circle

The diameter of the inscribed circle may range between 15 m and 100 m. A
minimum diameter of 37 m is required for roundabouts on the State
highway system, because smaller circles do not adequately accommodate
truck movements. However, the safety advantages of a roundabout may
begin to diminish when the diameter of the inscribed circle exceeds 75
m.

## Circulatory Roadway

The width of the circulatory roadway depends mainly on the number of
entry lanes and the radius of vehicle paths. The roadway must be at
least as wide as the maximum entry width, and lane lines within the
circle should not delineated. The pavement may be either crowned or
sloped to one side, depending on the need to facilitate drainage or
minimize adverse crossfalls for vehicle paths.

## Central Island

The central island is usually delineated by a raised curb, and its size
is determined by the width of the circulatory roadway and the diameter
of the inscribed circle.

## Truck Apron

A truck apron may be needed on smaller roundabouts to accommodate the
wheel path of oversized vehicles. The apron is usually designed as a
mountable portion of the central island.

## Splitter Island

This splitter island is placed within the leg of a roundabout to
separate entering and exiting traffic. It is usually designed with
raised curb to deflect entering traffic and to provide a refuge for
pedestrian crossings.

## Bypass Lane

A bypass lane may be warranted for heavy right turn volumes.

## Pedestrian Crossing

The location of pedestrian crossing is generally recommended to be one
to three vehicle lengths behind the yield line. Bringing crossings
closer to the circle would reduce roundabout capacity, while placing
them further away would expose pedestrians to higher speeds.

## Approach Width

This approach width refers to the half of the roadway that is
approaching the roundabout.

## Departure Width

This departure width refers to the half of the roadway that is departing
the roundabout.

## Entry Width

The entry width is the perpendicular distance from the right curb line
of the entry to the intersection of the left edge line and the inscribed
circle.

## Exit Width

The exit width is the perpendicular distance from the right curb line of
the exit to the intersection of the left edge line and the inscribed
circle.

## Flare

A flare may be used to increase the capacity of a roundabout by
providing additional lanes at the entry. Because flared entries tend to
increase the potential for accidents, they should be used only when
required by traffic volumes.

## Entry Angle

To provide the optimum deflection for entering vehicles, the angle of
entry should be approximately 30 degrees. Smaller angles reduce
visibility to the driver\'s left, while larger angles cause excessive
braking on entry and a resulting decrease in capacity.

## Entry Radius

The entry radius is the minimum radius of curvature measured along the
right curb at entry. The practical entry radius is approximately 20 m.
Smaller radii may decrease capacity, while larger radii may cause
inadequate entry deflection.

## Exit Radius

The exit radius is the minimum radius of curvature measured along the
right curb at exit. The desirable exit radius is approximately 40 m.

# Traffic operations

## Capacity

Roundabout capacity is defined as the sum of all entering approach
capacities. Capacity of each entry is defined as the maximum number of
vehicles that can enter the roundabout within 1 hour; this is defined
for a given volume of circulating vehicles. This is similar in concept
to the analysis method of the Highway Capacity Manual HCM "Chapter 10"
for unsignalized intersection capacity, whereby the capacity of each
minor traffic stream is defined separately, depending in the critical
gap and the conflicting traffic-stream volume. Linear regression
equations have been developed to describe the relationship between the
entry capacity (Ve) of an approach and the circulating traffic volume
(Vc). Error: Reference source not found6 presents these parameters.

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[]{#__RefHeading___Toc509223509 .anchor}Figure 6. Entry capacity and
circulating flow parameters (Polus and Shmueli, 1997)

Generally, there are two approaches to calculating the capacity of a
roundabout. The British method involves an empirical formula based on
measurements at saturated roundabouts, whereas the Australian method
uses an analysis based on gap acceptance. A draft update of the Highway
Capacity Manual (HCM) includes a procedure for determining the capacity
of single-lane roundabouts using the gap acceptance approach. For
analyzing multi-lane roundabouts, the draft HCM suggests the use of
software programs, but no specific program is mentioned. It is
recognized that there are advantages to using empirical models to
develop relationships between geometric design characteristics and
roundabout performance. However, given the current lack of field data in
the United States, the draft HCM recommends using the analytical
approach. Although both approaches are currently acceptable, the
fundamental differences between the empirical and analytical methods may
sometimes produce inconsistent results. The two methods are described as
follows:

## Empirical (British) Method 

In the British method, the capacity formula is based on the relationship
between entry capacity and various geometric parameters. For example,
the capacity of each approach to a roundabout decreases linearly as the
entry angle increases. Other parameters include entry width, approach
width, entry radius, and inscribed circle diameter. Two computer
software packages commonly used to calculate capacities, queues, and
delays in accordance with the British formula are ARCADY (Assessment of
Roundabout CApacity and DelaY) and RODEL (ROundabout DELay). Statistical
tests have been performed to confirm the suitability of the geometric
parameters used to predict capacity, and the output of both computer
programs have been verified through direct field observations.

## Analytical (Australian) Method 

In the Australian method, the capacity of a roundabout is calculated
using a traditional gap acceptance approach that is similar to the
process described in the HCM for analyzing two-way stop-controlled
intersections. It is assumed that drivers need a minimum \"critical
gap\" in the circulating flow before entering the roundabout. As the
available gaps become larger, more than one driver can enter with
subsequent headways equal to the \"follow-up time\". The capacity
formula calculates the capacity of each approach as a function of the
circulating flow, the critical gap, and the follow-up time. SIDRA
(Signalized and unsignalized Intersection Design and Research Aid) is
the computer software package commonly used for predicting the
performance of roundabouts by applying the gap-acceptance methodology.

## Comparison between Roundabout Capacity Models

Given that no capacity models are yet developed in the United States,
equations from foreign sources may temporarily be used to conduct
capacity analysis. Error: Reference source not found7 shows models
developed in England, Australia, Switzerland, and Germany. English and
Australian models include the outside diameter "D" (see Error: Reference
source not found6). The German and Swiss models do not depend on the
diameter and therefore, they can be adopted only for general planning
rather than for detailed designs.

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[]{#__RefHeading___Toc509223510 .anchor}Figure 7. International
comparison of entry capacities for single-lane roundabouts

(Brilon and Vandehey, 1998)

Brilon and Vandehey (1998) found that entry capacity is significantly
affected by human behavior, particularly personal attitudes and
experience. Because all these behavior elements are variable, capacity
at roundabouts is generally expected to be much more variable than for
signalized intersections. Table 2 summarizes modeling effort done by
Brilon (1998, Germany).

[]{#__RefHeading___Toc509223604 .anchor}Table 2. Entry Capacity
Equations for Roundabouts (Brilon and Vandehey, 1998)

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  height="2.4277777777777776in"}

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Based on applications in Germany, compact single-lane roundabouts have
many advantages for intersection with traffic volumes of up to 25,000
vpd. However, this amount can be increased by using a right-hand
"bypass" or "slip" lane for high-volume, right turn flow (see Error:
Reference source not found8).

  ---------------------------------------------------- -----------------------------------------------------
  ![](media/image9.png){width="1.8944444444444444in"   ![](media/image10.png){width="3.9118055555555555in"
  height="2.165277777777778in"}                        height="2.1868055555555554in"}

  ---------------------------------------------------- -----------------------------------------------------

[]{#__RefHeading___Toc509223511 .anchor}Figure 8. Roundabout with
right-turn bypass lane

(Public Roads, Autumn 1995)

## 

## Delay

Roundabout delay is defined separately for each entry approach. The
delay for any entry approach is composed of two distinct components:
queuing and geometric delay. Queuing delay occurs when drivers are
waiting for an appropriate gap in the circulating traffic. Geometric
delay results from vehicles slowing down as they traverse the roundabout
(i.e., driving through circulating lane).

To avoid long queues and delays, traffic demands must not exceed the
design capacity for all entry approaches, as is the case at any
intersection. Error: Reference source not found9 shows average delay
versus reserve capacity. Reserve capacity is an indication for how busy
the entry approach. Based on this figure if the demand flow of a given
approach entry is 100 pcph below the design capacity, average delay
should remain below 35 seconds per vehicle.

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  height="2.6847222222222222in"}

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[]{#__RefHeading___Toc509223512 .anchor}Figure 9. Average delay versus
reserve capacity (Brilon and Vandehey, 1998)

When comparing a roundabout's operation with that of a traffic signal,
it is important to recognize that outside the intersection's peak hours
(i.e., traffic demands are lower), roundabouts result less delay to
motorists, whereas a signal will always result more delay, even under
extremely low flow conditions.

## Safety 

Reduced speeds at roundabouts have been shown to be the primary cause of
improving safety. Another factor is the reduced number of conflict
points as compared to conventional intersection.

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  height="2.098611111111111in"}

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[]{#__RefHeading___Toc509223513 .anchor}Figure 10. Potential conflict
points between an intersection and a roundabout

(Bared *et al*, 1997)

Accident predication models for roundabouts have been developed in terms
of entering traffic, circulating traffic, and geometric features such as
entry path curvature, entry width, circulating width, and central
diameter. Accident models are classified by accident types for a given
entry approach. Bared *et a* (1997) presented the following accident
model for roundabouts.

$$A = \text{kQ}^{a}(\text{or}\text{ Q}_{e}^{\alpha}Q_{c}^{\beta})\text{exp}(\sum_{}^{}{b_{i}X_{i})}$$

![](media/image13.png){width="4.83125in" height="2.227777777777778in"}

Error: Reference source not found11 provides examples for these accident
models. This figure confirms that roundabouts experience fewer and lower
severity than stop and signalized intersections. The most safety
sensitive design elements of roundabouts are entry width and circulating
width. Widening of both entry and circulating widths increases accident
frequency. However, capacity of roundabout does increase as entry and
circulating widths increases. Keep in mind, that capacity often
conflicts with safety.

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  height="2.7402777777777776in"}

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[]{#__RefHeading___Toc509223514 .anchor}Figure 11. Examples for accident
models for roundabout and signalized intersections

(Bared *et al*, 1997)

# Advantages of Roundabouts

## Less Serious Accidents 

Head-on and angle collisions are virtually non-existent because of the
circular rather than opposing flow of traffic. The angles of traffic
interaction and slower speed through the interchange reduce the severity
of accidents. Roundabouts in the USA and other countries have achieved a
50 to 90 percent reduction in collisions compared to intersections using
2- or 4-way stop control or traffic signals
(<http://www.islandnet.com/ITE_BC/No95_Roundabout.html>).

## Construction, Operating, and Maintenance Costs

A simple signalized intersection costs about \$3,000 (US) per year for
electricity, maintenance of loops, controller, signal heads, timing
plans, etc. In addition, signal heads and controllers have to be
replaced and completely rebuilt on a regular basis. Larger signalized
intersections are more expensive to maintain. The only maintenance costs
for a roundabout are for landscape maintenance and occasional sign
replacement.

Small roundabouts only cost several thousand dollars. Larger roundabouts
can cost as much or more than a set of traffic signals. Even if the
construction cost of a roundabout is higher than traffic signals, a life
cycle economic analysis including construction, operation, maintenance
and collision cost reduction of each type of control will usually show
that a roundabout has a higher benefit/cost ratio than signalized
intersection.

## Self Regulating

Traffic flows change with time and development. To provide optimum
operation, traffic signals need to be retimed regularly. As traffic
volumes increase, especially cross-traffic volumes, additional
intersection lanes need to be added so the intersection capacity can
approach that of the mid-block segment. In most cases the whole road is
widened. In contrast, the capacity of a roundabout can approach the
mid-block capacity of the intersecting roads. Although as the
cross-traffic volumes increase, short approach lanes and/or an
additional circulating lane may be added. The resulting roadwork and
right-of-way requirements are much less than for the signal controlled
intersection. Generally a well-designed roundabout closely matching
approach and mid-block capacity, rarely needs altering, except where the
road is widened and the number of approach lanes increased.

## Environmental benefits

Brilon (1998) mentioned that German and other countries indicate that
roundabouts account for a reduction in noise levels. Roundabout also can
be expected to result in a lower pollutant output as the result of fewer
vehicle stops and starts.

# Disadvantages of Roundabouts

## Flat Area

Roundabouts should be considered only in areas that can accommodate an
acceptable outside diameter and other appropriate geometric design
elements. To provide adequate sight distance for approaching drivers to
perceive the layout of the intersection, the roundabout should be
preferably located either on level terrain or at the bottom of a sag
vertical curve. The topography should also allow the circle of the
roundabout to be constructed on a flat plateau to provide visibility
within the intersection.

## Signal Coordination

Roundabouts are not suitable in areas with a coordinated traffic signal
system, because such systems break down when the progression of platoons
is disrupted by the unregulated movement of a roundabout. Conversely, a
roundabout should not be constructed at a location where the flow of
vehicles leaving the intersection would be obstructed by queues from
downstream traffic controls.

## Unbalanced Flow

Roundabouts may not be effective at intersections where entry flows are
unbalanced. When the volume on the major road is much heavier than that
on the minor road, the equal treatment of approaches may cause undue
delay to the major road. Also, if the major road carries a heavy stream
of through-traffic, the lack of adequate gaps in the dominant flow may
prevent the minor flow from entering the roundabout.

## Pedestrians / Bicyclists Safety

Additional assessment is warranted prior to constructing roundabouts in
areas where pedestrian or bicycle activity is expected. With the absence
of conventional crossing controls, many pedestrians do not perceive
roundabouts to be safe. Despite this perception, accident records
indicate that with the use of proper design elements, a pedestrian is at
least as safe at a roundabout as at a conventional intersection.
However, the safety record for bicyclists appears to be more
problematic.

# MODELING AND SIMULATION

The theory of gap-acceptance leads to complex assumptions regarding
driver behavior. Various simplifications need to be made in order to
obtain less complicated model. Although simulation models have many
advantages, it should be noted that the need for data is great. Since
simulation models are dependent on driver behavior, the criticism
directed at gap-acceptance models is also valid.

Simulation techniques involving complex computer programs have been
developed in the last decade, which require considerable computing
power. These are used in a number of countries to model behavior at
non-signalized intersections, but only some have been adapted to
roundabouts. The earlier role of simulation models of entry capacity,
delay, and accident risk is changing from an instrument of scientific
research towards a practical tool for the traffic engineer.

Simulation models have been developed or investigated in Australia,
France, Germany, England and Switzerland. The development of a
simulation model (INSECT) in Australia has indicated that fixed gap
times are not applicable, and there are differences of gap-acceptance
characteristics between sign controlled intersections and roundabouts,
where gaps acceptance depends on waiting time. The model attempts to
simulate the movements of individual vehicles every second. It contains
five sub-models: drivers, vehicle generation, lane selection, standard
conflict resolution, and roundabout conflict resolution. The latter
considers also the closest approach on the right. Gap-acceptance methods
are used to resolve the conflicts. Small roundabouts are not modeled
very well. Results, surveyed and simulated queue delays, confirms that
for most cases the model predictions are reasonably accurate. Further
development in the field of crash prediction is possible.

## Compute Programs

Since roundabout design is fairly new, there are very few programs
developed that are used for analysis of roundabouts. Modifying the
results of present day intersection analysis programs form many of these
programs. Some of the more popular programs are RODEL, ARCADY, SIDRA,
KREISEL, GIRABASE, and HCM (Highway Capacity Manual). Of these programs,
SIDRA is the most commonly used.

## SIDRA

The SIDRA (Signalized & unsignalized Intersection Design and Research
Aid) package has been developed by ARRB Transport Research in Australia,
as an aid for design and evaluation of the following intersection types:

-   Signalized intersections

-   Roundabouts

-   Two-way stop control

-   All-way stop control

-   Yield sign control

Recent Australian research shows that if there is more than one entry
lane, the traffic flow differs between the lanes. The lane with the
greatest flow is called the dominant stream and the other lanes are
termed the sub-dominant streams.

The gap-acceptance parameters are calculated in the following order:

-   The follow up time in the dominant stream is estimated as a function
    of the circulating flow and the inscribed circle diameter;

-   The follow up time in the sub-dominant stream is calculated as a
    function of the ratio of flows between the lanes considered and the
    dominant-stream follow up time;

-   The critical gap is calculated as a function of the follow up time,
    the major flow, the number of effective circulating lanes and the
    entry lane width.

All capacity estimates are based on gap acceptance modeling. SIDRA
computes the capacity of each approach lane separately. This method
allows for capacity losses due to lane under-utilization and allocated
the largest degree of saturation in any lane movement (Kerenyi, 1998).

SIDRA requires site specific data covering traffic volumes by movement,
number of entry and circulating lanes, central island diameter, and
circulating roadway width. It uses several parameters for which
reasonable default values are offered.

One parameter of particular importance is the practical capacity of
roundabouts. The default value of 85% of the possible capacity (i.e. v/c
= 0.85). The SIDRA documentation points out that roundabout operation at
near capacity levels is less predictable than signal operation. This is
because signal control is more positive, and therefore less dependent on
drivers' behavior. Therefore, more caution is urged in dealing with
roundabouts that operate above the practical capacity. The concept of
geometric delay is added to the queuing delay. Geometric delay is the
delay experienced by drivers within the roundabout due to a negotiation
speed that is slower that the approach speed. SIDRA offers the option to
include or exclude the geometric delay from computations. Technically, a
delay that includes the geometric delay provides a more realistic
assessment of roundabout performance (FDOT, 1996).

## RODEL

RODEL is an interactive program intended for the evaluation and design
of roundabouts. This program was developed in the Highways Department of
Staffordshire County Council in England. RODEL is based on an empirical
model developed by Kimber at the Transport and Road Research Lab (TRRL)
in the UK. The empirical model was chosen over the gap acceptance model
because it directly related capacity to detailed geometric parameters.
RODEL is an interactive program in which simultaneous display of both
input and output data is shown in a single screen. There are two main
modes of operation. In mode 1, the user specifies a target parameter for
average delay, maximum delay, maximum queue, and maximum v/c ratio.
RODEL generates several sets of entry geometrics for each approach based
on the given input. Depending on site specifics and constraints, the
generated geometrics can be used for design purposes. Mode 2 focuses
more on performance evaluation using specified values of the geometric
and traffic characteristics.

## ARCADY

ARCADY is a British roundabout analysis program which has the same
theoretical background as RODEL. This program also incorporates Kimber's
model which is based on the rule of circulating vehicles having priority
over entry vehicles. Kimber used the idea of entry geometry affecting
the capacity and related the equation to several site-specific
parameters. The model also assumes a linear relationship between the
circulating flow and the maximum entry flow. The ARCADY input data
requirements are similar to RODEL since both programs follow the same
methodology. The input parameters include entry width, inscribed circle
diameter, flare length, approach road width, entry radius, and entry
angle. Like RODEL, ARCADY deals in the concept of confidence level. The
main difference is that the confidence level may be specified for RODEL,
but is embedded in the ARCADY model at 50 percent.

## KREISEL

Developed in Germany, it offers many user-specified options to implement
the full range of procedures found in the literature from Europe and
Australia. KREISEL gives the average capacity from a number of different
procedures. It provides means to compare these procedures.

## GIRABASE

Is a French method. Capacity, delay, and queuing projections based on
regression. Sensitive to geometric parameters. Gives average values.

## HCM Software

US HCM method. Limited to capacity estimation based on entering and
circulating volume. Optional gap acceptance parameter values provide
both a liberal and conservative estimate of capacity. The data used to
calibrate the models were recorded in the US. The two curves given
reflect the uncertainty from the results. The upper bound average
capacities are anticipated at most roundabouts. The lower bound results
reflect the operation that might be expected until roundabouts become
more common.

# summary and conclusions

Modern roundabouts are circular intersections that have been
successfully implemented in Europe and Australia over the past few
decades. Despite the approximately 35,000 roundabouts in operation
around the world, there are fewer than 50 that exist in the United
States. Modern roundabouts are distinguished from traffic circles by;
(1) the \"yield-at-entry\" rule in which approaching vehicles must wait
for a gap in the circulating flow before entering the circle, (2)
parking is not allowed on the circulating roadway, and (3) no pedestrian
activities take place on the central island.

Roundabout capacity is defined as the sum of all entering approach
capacities. Capacity of each entry is defined as the maximum number of
vehicles that can enter the roundabout within 1 hour; this is defined
for a given volume of circulating vehicles. Linear regression equations
have been developed to describe the relationship between the entry
capacity (Ve) of an approach and the circulating traffic volume (Vc).

Because roundabouts have only begun to appear in the U.S., there is a
lack of empirical data regarding the volume at which a roundabout begins
to break down. Until further data is available, roundabouts on the State
highway system should be considered only at intersections where volumes
generally do not exceed 5000 vehicles per hour. Regardless of whether
the proposal involves a new facility or an operational improvement, the
design of a roundabout should be based on estimated traffic 20 years
after the completion of construction.

Our investigation showed many advantages to roundabouts, including
safety and delay benefits. It is therefore suggested that roundabouts be
considered as alternatives to intersections that experience or expected
to experience high crash rates or delay levels. Developing a simulation
tool for roundabouts is recommended to evaluate existing roundabouts or
comparing roundabouts to intersections.

There is a need for an efficient tool that would enable traffic analysts
to evaluate different combinations of design and traffic factors and
propose efficient designs in a timely manner. When interactions between
design factors are so complex, such as the case of roundabout design;
simulation techniques proved to be the most efficient tools to support
the design function. The simulation program will need to include a model
of driver behavioral patterns, including the gap acceptance process. The
definition of delay is critical during the validation of the program. If
delays are taken as those incurred by vehicles on the approaches to the
roundabout, then delays from queues observed will need to be compared to
the simulated delays.

# biblography

Bared, J., Prosser, W., and Esse, C., (1997) "State-of-the-art design of
roundabouts", *Transportation Research Record* 1579.

Brilon, W., Vandehey, M., (1998) \"The state of the art in Germany\",
*ITE journal*

Florida roundabout guide, Florida Department of Transportation, 1996.

Kerenyi L (1998) "A Comparison of a Traffic Signal Controlled Junction
and a Roundabout Solution at the Sluppen Bridge Junction in Trondheim",
Master's thesis, Norwegian University of Science and Technology.

Polus, A., and Shmueli, S., (1997) "Analysis and evaluation of the
capacity of roundabouts", *Transportation Research Record* 1572

Public Roads (Autumn 1995),
<http://www.tfhrc.gov/pubrds/fall95/p95a41.htm>

<http://www.islandnet.com/ITE_BC/No95_Roundabout.html>

<http://roundabouts.kittelson.com/crossref.html>

# 

# 

# 

# 

# 

# 

# 

# Appendix 

**ROUNDABOUTS IN THE U.S.**

Status: Existing

  -------------------------------------------------------------------------------------------
  **State**   **County**     **City**           **Intersection**                **Type**
  ----------- -------------- ------------------ ------------------------------- -------------
              N/A            (unincorporated)   inv.cgi?site_id=140             

  CA          Alameda        Berkeley           Marin Ave./Los Angeles Ave./Del 
                                                Norte St./Arlington Ave.        

  CA          Humboldt       Arcata             West End @ Spear                Single-Lane

  CA          Los Angeles    Long Beach         Los Alamitos Circle (Hwy. 1/Hwy Multi-Lane
                                                19/Los Coyotes Diagonal)        

  CA          Santa Barbara  Santa Barbara      Alameda Padre Serra/Montecito   Single Lane
                                                St./Salinas St./Sycamore Canyon 
                                                Rd.                             

  CO          N/A            Avon               Avon Rd./Beaver Creek Blvd.     Multi-Lane

  CO          N/A            Avon               Avon Rd./Benchmark Rd.          Multi-Lane

  CO          N/A            Avon               Avon Rd./I-70 EB Ramps          Multi-Lane

  CO          N/A            Avon               Avon Rd./I-70 WB Ramps          Multi-Lane

  CO          N/A            Avon               Avon Rd./US 6                   Multi-Lane

  CO          N/A            Nederland          Hwy 72/Hwy 119/2nd St./Bridge   Single Lane
                                                St.                             

  CO          N/A            Vail               Chamonix Rd./I-70 EB            Multi-Lane
                                                Ramps/South Frontage Rd.        

  CO          N/A            Vail               Chamonix Rd./I-70 WB            Multi-Lane
                                                Ramps/North Frontage Rd.        

  CO          N/A            Vail               Vail Road/I-70 EB Ramps/South   Multi-Lane
                                                Frontage Rd.                    

  CO          N/A            Vail               Vail Road/I-70 WB Ramps/North   Multi-Lane
                                                Frontage Rd./Spraddle Cr. Rd.   

  DC          N/A            Washington         Chevy Chase Circle (Conn.       
                                                Ave./Western Ave.)              

  DC          N/A            Washington         Dupont Circle (Mass Ave./Conn.  
                                                Ave./New Hampshire Ave.19th     
                                                St./P St.)                      

  DC          N/A            Washington         Grant Circle (New Hampshire     
                                                Ave./Illinois Ave./NW 5th St.)  

  DC          N/A            Washington         Logan Circle (Rhode Isl.        
                                                Ave./Vermont Ave./13th St./P    
                                                St.)                            

  DC          N/A            Washington         Scott Circle (Mass. Ave./Rhode  
                                                Isl. Ave./16th St./N St.)       

  DC          N/A            Washington         Sheridan Circle (Mass Ave./23rd 
                                                St./R St.)                      

  DC          N/A            Washington         Sherman Circle (Kansas          
                                                Ave./Illinois Ave.)             

  DC          N/A            Washington         Tenley Circle (Conn.            
                                                Ave./Nebraska Ave.)             

  DC          N/A            Washington         Thomas Circle (Mass             
                                                Ave./Vermont Ave./14th St./M    
                                                St.)                            

  DC          N/A            Washington         Ward Circle (Mass.              
                                                Ave./Nebraska Ave.)             

  DC          N/A            Washington         Washington Circle (Penn.        
                                                Ave./New Hampshire Ave./23rd    
                                                St./K St.)                      

  DC          N/A            Washington         Westmoreland Circle (Mass.      
                                                Ave./Dalecarlia Pkwy/Western    
                                                Ave.)                           

  FL          Alachua        Gainesville        SE 7th Street/SE 4th Avenue     Single Lane

  FL          Broward        Hollywood          Hollywood Blvd./26th Ave.       Multi-Lane

  FL          Broward        Hollywood          Hollywood Blvd./Rainbow Dr.     Multi-Lane

  FL          Broward        Hollywood          Hollywood Blvd./S. Federal Hwy. Multi-Lane
                                                (US 1)/Harrison St./Tyler St.   

  FL          Collier        Naples             7th St. N./11th Ave. N.         Single Lane

  FL          Collier        Naples             7th St. N./12th Ave. N.         Single Lane

  FL          Collier        Naples             7th St. N./3rd Ave. N.          Single Lane

  FL          Collier        Naples             7th St. N./7th Ave. N.          Single Lane

  FL          Collier        Naples             8th St. S./12th Ave. S.         Single Lane

  FL          Hillsborough   Tampa              North Blvd./Country Club        Single Lane

  FL          Lake           Lady Lake          ()                              Multi-Lane

  FL          Lake           Lady Lake          ()                              Multi-Lane

  FL          Lake           Tavares            Main St./Disston Ave./Lake Dora Single Lane
                                                Dr.                             

  FL          Leon           Tallahassee        Killarney Way/Shamrock Drive    Single Lane

  FL          Manatee        Bradenton Beach    SR 789/Bridge Street            Single Lane

  FL          Martin         Stuart             Federal Hwy (US 1)/SR 76/SR A1A Single Lane

  FL          Martin         Stuart             N. Colorado Ave./E. Osceola St. Single Lane

  FL          N/A            (unincorporated)   inv.cgi?site_id=138             

  FL          Okaloosa       Fort Walton Beach  Hollywood Blvd./Doolittle Blvd. Single Lane

  FL          Palm Beach     Boca Raton         SW 18th St./Juana Rd. (SW 12th  Single Lane
                                                Ave.)                           

  FL          Palm Beach     West Boca Raton    Lakes at Boca Raton/Cain Blvd.  Single Lane

  FL          Sarasota       Sarasota           South Gate Circle (Tuttle       Multi-Lane
                                                Ave./Siesta Dr.)                

  FL          Sarasota       Sarasota           St. Armands Circle (SR          Multi-Lane
                                                780/Blvd. of the                
                                                Presidents/John Ringling Blvd.) 

  MD          Anne Arundel   Lothian            MD 2/MD 408/MD 422              Single Lane

  MD          Baltimore      Towson             MD 45/MD 146/Joppa              Multi-Lane
                                                Rd./Allegheny Ave.              

  MD          Carroll        Taneytown          MD 140/MD 832                   Multi-Lane

  MD          Cecil          Leeds              MD 213/Leeds Road/Elk Mill Road Single Lane

  MD          Harford        Bel Air            Tollgate Rd. & Marketplace Dr.  Single-Lane

  MD          Howard         (unincorporated)   Baneker Rd.                     

  MD          Howard         (unincorporated)   MD 103/MD 100 EB Ramps          Single Lane

  MD          Howard         (unincorporated)   MD 103/MD 100 WB Ramps          Single Lane

  MD          Howard         (unincorporated)   Trotter Rd.                     

  MD          Howard         Lisbon             MD 94/MD 144                    Single Lane

  MD          Montgomery     Gaithersburg       Longdraft Rd./Kentlands         Multi-Lane

  MD          Prince         (unincorporated)   Ft. Washington Rd.              
              George\'s                                                         

  MD          Washington     Cearfoss           MD 63/MD 58/MD 494              Single Lane

  ME          N/A            Gorham             Rte. 202/Rte. 4/Rte. 237        

  MS          Hinds          Jackson            MS 475/Airport Rd./Old Brandon  Single Lane

  NV          N/A            Las Vegas          Lake South/Crystal Water Way    Single Lane

  NV          N/A            Las Vegas          Michael/Harmony Way             Single Lane

  NV          N/A            Summerlin          North Roundabout (Village       Multi-Lane
                                                Center Circle/Town Center       
                                                Drive/Library Hill Drive?)      

  NV          N/A            Summerlin          South Roundabout (Village       Multi-Lane
                                                Center Circle/Hill Center       
                                                Drive/Meadow Hills Drive?)      

  OR          Multnomah      Portland           NE 39th Ave./Glisan St.         Multi-Lane

  OR          Washington     Beaverton          SW Teal Blvd./155th             Single Lane
                                                Ave./Nutcracker Ct.             

  SC          N/A            Hilton Head        Whooping Crane/Main Street      Single Lane

  TX          N/A            Addison            Mildred St./Quorum Dr.          Multi-Lane

  VT          N/A            Montpelier         Keck Circle (Main St./Spring    Single Lane
                                                St.)                            

  WA          Kitsap         Port Orchard       Mile Hill Dr. (Hwy 166)/Bethel  Single-Lane
                                                Avenue                          
  -------------------------------------------------------------------------------------------

Status: Planned

  -----------------------------------------------------------------------------------------
  **State**   **County**   **City**           **Intersection**                **Type**
  ----------- ------------ ------------------ ------------------------------- -------------
  CA          Humboldt     Arcata             Samoa @ Buttermilk              Single-Lane

  CA          Humboldt     Arcata             Samoa @ Crescent                Single-Lane

  CA          Humboldt     Arcata             Samoa @ Union                   Single-Lane

  CA          Placer       Truckee            Donner Pass Rd./I-80 Ramps      

  FL          Palm Beach   Lake Worth         Lake Worth Ave. (SR 802)/South  Multi-Lane
                                              A Street                        

  KS          N/A                             Rice Rd./I-70 EB Ramps          

  KS          N/A                             Rice Rd./I-70 WB Ramps          

  MD          Anne Arundel (unincorporated)   Arundel Beach Road/Leelynn      Single Lane
                                              Drive                           

  MD          Anne Arundel Annapolis          Gateway Circle (West St./Taylor Multi-Lane
                                              Ave./Spa Rd.)                   

  MD          Anne Arundel Glen Burnie        Quarterfield Road (MD 174)/I-97 Multi-Lane
                                              SB Ramps                        

  MD          Baltimore    (unincorporated)   Charles St./Bellona Ave.        Single Lane

  MD          Baltimore    (unincorporated)   MD 372/Hilltop Rd.              

  MD          Caroline     Federalsburg       MD 307/MD 318                   Single Lane

  MD          Cecil        (unincorporated)   MD 291/US 301 NB Ramps          Single Lane

  MD          Cecil        (unincorporated)   MD 291/US 301 SB Ramps          Single Lane

  MD          Frederick    Brunswick          MD 17/A St./B St./Maryland Ave. Single Lane

  MD          Harford      Abingdon           Tollgate Pkwy. & Singer Rd.     Single-Lane

  MD          Howard       (unincorporated)   Hopkins-Gorman Rd./US 29 SB     Multi-Lane
                                              Ramps                           

  MD          Howard       (unincorporated)   MD 104/MD 100 WB Ramps          Multi-Lane

  MD          Howard       (unincorporated)   MD 216/US 29 NB Ramps           Multi-Lane

  MD          Howard       (unincorporated)   MD 216/US 29 SB Ramps           Multi-Lane

  MD          Howard       (unincorporated)   Snowden River Pkwy./MD 100 WB   Single Lane
                                              Ramps                           

  MD          Howard       Lisbon             MD 94/Old Frederick Rd.         

  MD          Prince       Mt. Rainier        US 1/34th St.                   Multi-Lane
              George\'s                                                       

  MD          Prince       Ritchie            Ritchie-Marlboro Rd./I-95 NB    Multi-Lane
              George\'s                       Ramps                           

  MD          Prince       Ritchie            Ritchie-Marlboro Rd./I-95 SB    Multi-Lane
              George\'s                       Ramps                           

  NJ          N/A          Southampton        Red Lion Circle                 

  NJ          N/A          Wall               Brielle Circle                  

  VT          N/A          Bennington         Rte. 67A                        

  VT          N/A          Brattleboro        Rte. 9/Rte. 5                   

  VT          N/A          Manchester         Rte. 7A/Equinox                 

  VT          N/A          Manchester         Rte. 7A/Grand Union             Single Lane

  VT          N/A          Richmond           Rte. 2/Rte. 117/I-89            

  VT          N/A          Stow               Rte. 108                        
  -----------------------------------------------------------------------------------------

Status: Proposed

  -------------------------------------------------------------------------------------------
  **State**   **County**   **City**           **Intersection**                  **Type**
  ----------- ------------ ------------------ --------------------------------- -------------
  CA          Alameda      Berkeley           Gilman St./I-80 Ramps             

  CA          Humboldt     Arcata             11^th^ @ D                        Single-Lane

  CA          Humboldt     Arcata             Alliance @ Foster                 Single-Lane

  CA          Humboldt     Arcata             Guintoli @ Heindon                Single-Lane

  CA          Humboldt     Arcata             US101NB @ 14^th^                  Single-Lane

  CA          Humboldt     Arcata             US101NB @ Sunset & LK Wood        Single-Lane

  CA          Humboldt     Arcata             US101NB @ Guintoli                Single-Lane

  CA          Humboldt     Arcata             US101SB @ Sunset                  Single-Lane

  CA          Humboldt     Arcata             US101SB @ Guintoli                Single-Lane

  CA          Los Angeles  Castaic            NorthLake Blvd./D St.             Single Lane

  CA          Los Angeles  Long Beach         Lakewood Blvd. (Hwy 19)/Outer     Multi-Lane
                                              Circle Dr.                        

  CA          N/A          Calabasas          Lost Hills Road/Agoura Rd         Multi-Lane

  CA          N/A          Calabasas          Lost Hills Road/US 101 NB Ramps   Multi-Lane

  CA          N/A          Carlsbad           Lego Dr./Armada Dr.               Multi-Lane

  CA          N/A          Fresno             Fresno St./N. Fresno              Multi-Lane
                                              St./Divisadero St.                

  CA          Nevada       Grass Valley       Hwy 49/McKnight Rd.               

  CA          Orange       (unincorporated)   Conroy-Windermere                 Multi-Lane
                                              Rd./Apopka-Vineland Rd.           

  CA          Santa        Santa Barbara      Milpas St./US 101 WB              Multi-Lane
              Barbara                         Ramps/Carpinteria St.             

  CA          Sonoma       Sonoma             Hwy 12/Napa Rd.                   

  MD          Anne Arundel Glen Burnie        Quarterfield Road (MD 174)/I-97   Multi-Lane
                                              NB Ramps                          

  MD          Harford      (unincorporated)   MD 165/MD 23                      Single Lane

  MD          Harford      (unincorporated)   MD 165/MD 24                      Single Lane

  MD          Washington   Ringgold           MD 64/MD 418                      Single Lane

  MD          Worcester    Ocean City         US 113/MD 589                     
  -------------------------------------------------------------------------------------------

Status: Removed

  ------------------------------------------------------------------------------------
  **State**   **County**   **City**     **Intersection**                  **Type**
  ----------- ------------ ------------ --------------------------------- ------------
  FL          Palm Beach   West Palm    S. Quadrille Blvd. (El Campeon    Single Lane
                           Beach        Blvd.)/Fern St.                   

  FL          Volusia      Daytona      Seabreeze Circle(Seabreeze        Multi-Lane
                           Beach        Bridge/Mason Ave./Ballough Dr.)   
  ------------------------------------------------------------------------------------