**Table of Contents**

**List of
Exhibits**....................................................................................iii

**List of
Tables**......................................................................................iv

[**1.** **Introduction** 1](#introduction)

[1.1 Using This Manual 1](#using-this-manual)

[1.2 Definition of Ramp Meters 1](#definition-of-ramp-meters)

[1.3 Purpose of Ramp Meters 1](#purpose-of-ramp-meters)

[1.4 Benefits of Ramp Meters 1](#benefits-of-ramp-meters)

[1.4.1 Temporal Shift of Demand 2](#temporal-shift-of-demand)

[1.4.2 Spatial Shift of Demand 3](#spatial-shift-of-demand)

[1.4.3 Modal Shift 3](#modal-shift)

[1.4.4 Collision Reduction 3](#collision-reduction)

[1.5 Drawbacks of Ramp Meters 4](#drawbacks-of-ramp-meters)

[1.6 Application of Recommendations 4](#application-of-recommendations)

[**2.** **Ramp Meter Warrants** 5](#ramp-meter-warrants)

[2.1 Purpose of Warrant Process 5](#purpose-of-warrant-process)

[2.2 Geographic Scope of Study 5](#geographic-scope-of-study)

[2.3 Data Requirements 5](#data-requirements)

[2.4 Individual Warrants 5](#individual-warrants)

[2.4.1 Warrant One -- Recurring Congestion Warrant^7^
6](#warrant-one-recurring-congestion-warrant7)

[2.4.2 Warrant Two -- Collision History Pattern^7^
6](#warrant-two-collision-history-pattern7)

[2.4.3 Warrant Three -- Freeway Level of Service^7^
6](#warrant-three-freeway-level-of-service7)

[2.4.4 Warrant Four -- Modal Shift^7^ 6](#warrant-four-modal-shift7)

[2.4.5 Warrant Five -- Redistribution of Access^7^
6](#warrant-five-redistribution-of-access7)

[2.4.6 Warrant Six -- Sporadic Congestion Warrant^7^
7](#warrant-six-sporadic-congestion-warrant7)

[2.4.7 Warrant Seven: Total Volume Warrant^9^
7](#warrant-seven-total-volume-warrant9)

[2.4.8 Warrant Eight: Right Lane plus Ramp Volume Warrant^9^
7](#warrant-eight-right-lane-plus-ramp-volume-warrant9)

[2.4.9 Warrant Nine: Geometric Warrant^9^
7](#warrant-nine-geometric-warrant9)

[2.5 Overall Ramp Metering Warrant 8](#overall-ramp-metering-warrant)

[2.6 Warrant Analysis Example 8](#warrant-analysis-example)

[**3.** **Ramp Meter Design** 11](#ramp-meter-design)

[3.1 Introduction 11](#introduction-1)

[3.2 Design Volume 11](#design-volume)

[3.3 Choosing the Number of Lanes to Meter
11](#choosing-the-number-of-lanes-to-meter)

[3.4 Freeway Entrance Types 12](#freeway-entrance-types)

[3.4.1 Taper Type Entrances 12](#taper-type-entrances)

[3.4.2 Parallel Type Entrances 14](#parallel-type-entrances)

[3.4.3 Design Guidelines Choosing Entrance Types
15](#design-guidelines-choosing-entrance-types)

[3.5 Design Guidelines for Placement of Stop Bars
15](#design-guidelines-for-placement-of-stop-bars)

[3.6 Design Guidelines for Queue Storage
16](#design-guidelines-for-queue-storage)

[3.7 Design Guidelines for the Removal of HOV Preferential Lanes
17](#design-guidelines-for-the-removal-of-hov-preferential-lanes)

[3.8 Design Guidelines for the Installation of HOV Preferential Lanes
for Ramps
17](#design-guidelines-for-the-installation-of-hov-preferential-lanes-for-ramps)

[3.9 Design Guidelines for Ramp Meter Enforcement Areas
18](#design-guidelines-for-ramp-meter-enforcement-areas)

[3.10 Single Lane Metered Ramp Design
20](#single-lane-metered-ramp-design)

[3.11 Dual Lane Metered Ramps 23](#dual-lane-metered-ramps)

[3.12 Ramp Meter Retrofit Applications
25](#ramp-meter-retrofit-applications)

[3.12.1 One-Lane Ramp Meter to Two-Lane Ramp Meter Conversion
25](#one-lane-ramp-meter-to-two-lane-ramp-meter-conversion)

[3.12.2 One-Lane + HOV Conversion to Two-Lane Ramp Meter
28](#one-lane-hov-conversion-to-two-lane-ramp-meter)

[3.13 Ramp Meter Hardware 31](#ramp-meter-hardware)

[3.13.1 Signals 31](#signals)

[3.13.2 Beacons 34](#beacons)

[3.13.3 Mainline Detectors 35](#mainline-detectors)

[3.13.4 Ramp Detectors 37](#ramp-detectors)

[3.13.5 Cabinet Assembly 41](#cabinet-assembly)

[3.14 Ramp Meter Pavement Marking 47](#ramp-meter-pavement-marking)

[3.15 Ramp Meter Signing 49](#ramp-meter-signing)

[3.16 Typical Conduit and Junction Box Layout
49](#typical-conduit-and-junction-box-layout)

[**4.** **Ramp Meter Operation** 51](#ramp-meter-operation)

[4.1 Ramp Meter Stand-Alone Local Operation
51](#ramp-meter-stand-alone-local-operation)

[4.2 Ramp Meters as an Element of the Freeway Management System
52](#ramp-meters-as-an-element-of-the-freeway-management-system)

[4.3 Communications with ADOT Traffic Operations Center
52](#communications-with-adot-traffic-operations-center)

[4.3.1 Ramp Meter Message Formats 53](#ramp-meter-message-formats)

[4.4 Integration with ADOT Traffic Operations Center
54](#integration-with-adot-traffic-operations-center)

[4.5 Ramp Metering Rate Selection 54](#ramp-metering-rate-selection)

[4.5.1 Arrival Discharge Chart 54](#arrival-discharge-chart)

[4.5.2 Computer Simulation 58](#computer-simulation)

[4.6 Ramp Metering Modes 58](#ramp-metering-modes)

[4.7 Ramp Metering Rates 59](#ramp-metering-rates)

[4.7.1 Ramp Meter as a Stand-Alone Strategy
60](#ramp-meter-as-a-stand-alone-strategy)

[4.7.2 Default Metering Rates 60](#default-metering-rates)

[4.7.3 Recommended Speeds 61](#recommended-speeds)

[4.7.4 Impact of Incidents 61](#impact-of-incidents)

[4.8 Ramp Meter Equity 62](#ramp-meter-equity)

[4.9 Enforcement of Ramp Meters 63](#enforcement-of-ramp-meters)

[**5.** **Ramp Meter Maintenance** 64](#ramp-meter-maintenance)

[5.1 Personnel 64](#personnel)

[5.2 Training 64](#training)

[5.3 Commonly Reported Malfunctions 65](#commonly-reported-malfunctions)

[5.4 Preventative Maintenance 65](#preventative-maintenance)

[5.5 Unscheduled Maintenance 66](#unscheduled-maintenance)

[5.6 Detection Maintenance 66](#detection-maintenance)

[5.7 Maintenance Documentation 67](#maintenance-documentation)

[5.8 Maintenance Evaluation 67](#maintenance-evaluation)

[**Acronyms** 68](#acronyms)

[**Glossary** 69](#glossary)

[**References** 71](#references)

List of Exhibits

Exhibit 2.1: Ramp Meter Warrant
Flowchart.........................................\......10

Exhibit 3.1: Tapered and Parallel Freeway Entrance
Types..........................13

Exhibit 3.2: Typical Ramp Meter Enforcement
Area....................................20

Exhibit 3.3: Single Lane Metered
Ramp...................................................22

Exhibit 3.4: Dual Lane Metered
Ramp...................................................\...26

Exhibit 3.5: One Lane to Two Lane Meter
Conversion.................................27

Exhibit 3.6: One Lane + HOV to Two Lane Meter
Conversion.......................30

Exhibit 3.7: Typical Ramp Meter Signal
Pole.............................................31

Exhibit 3.8: Ramp Meter Signal
Pole.......................................................33

Exhibit 3.9: Typical Flashing
Beacon.......................................................34

Exhibit 3.10: Flasher
Assembly............................................................\...36

Exhibit 3.11: Typical 341 Cabinet
Assembly..............................................41

Exhibit 3.12: 341 Controller Cabinet Foundation
Details..............................43

Exhibit 3.13: Model 179
Controller..........................................................44

Exhibit 3.14: Input File
Layout................................................................46

Exhibit 3.15: Ramp Meter Stop Bar
Striping..............................................48

Exhibit 3.16: Typical Ramp Meter
Sign.....................................................49

Exhibit 3.17: Typical Conduit and Junction Box
Layout................................50

Exhibit 4.1: Arrival Discharge Calculation Worksheet
Template.....................56

Exhibit 4.2: Arrival Discharge Calculation Worksheet
Example......................57

**List of Tables**

Table 1.1: Ramp Meter
Benefits............................................................\...2

Table 2.1: Total Volume Warrant
Criteria................................................\....7

Table 3.1: Recommended Number of
Lanes.............................................11

Table 3.2: Acceleration
Length...............................................................14

#  **Introduction**

## 1.1 Using This Manual {#using-this-manual .unnumbered}

This manual is intended to provide guidelines covering the design,
operation and maintenance of ramp meters on ADOT freeways for ADOT
design engineers, design consultants, operators, and maintenance
personnel, as well as city and county personnel working on ADOT
freeways. It is a supplement to, but does not supersede the ADOT Roadway
Design Guidelines (Publication \# 31-089), ADOT Standard Plans, ADOT
Standard Specifications, ADOT FMS Design Guidelines, Roadway Design
Memoranda, and other current design policies. This guidelines document
is not a textbook or a substitute for engineering knowledge, skill,
experience or judgment. It is not intended that any standard of conduct
or duty toward the public shall be created or imposed by this guideline.
Special situations may call for variations as conditions and experience
warrant.

## 1.2 Definition of Ramp Meters {#definition-of-ramp-meters .unnumbered}

Ramp meters are traffic control signals that control the flow of traffic
entering a freeway facility. ^7^

##  Purpose of Ramp Meters

Ramp metering is an effective traffic management strategy to maintain an
efficient freeway system and to protect the investment made in
constructing freeways by keeping them operating at or near capacity.^5^

The primary purpose of ramp metering is to mitigate recurring congestion
and associated collisions by spreading out queues of vehicles wishing to
enter the freeway over time. By spreading out queues, it also provides
for a safer merging of vehicles.

###  {#section .unnumbered}

## 1.4 Benefits of Ramp Meters {#benefits-of-ramp-meters .unnumbered}

Ramp meters are an operational strategy to reduce congestion and
increase safety on ADOT's freeway system. Typical benefits of ramp
meters include:

1.  Travel time savings

2.  Improved travel time reliability

3.  Reduction in number of collisions

4.  Increase in freeway throughput

The magnitude of the benefits varies widely depending on the nature of
the deployment and the operational policies for the ramp meter
installation. The prevailing Level of Service (LOS) of the mainline is
also a key factor in ramp meter effectiveness.

The Highway Capacity Manual indicates that at LOS A, the density is low
enough to allow smooth merging with virtually no impedance in the
traffic stream. Therefore, ramp meter usage during the free flow
conditions of LOS A does not offer benefits, as there are no flow
improvements to be made. At LOS B, the ability of vehicles to maneuver
within the traffic stream is slightly restricted, and ramp metering can
be slightly beneficial in improving merging operations by spreading the
queues out over time. At LOS C and D, the ability of vehicles to
maneuver within the traffic stream is noticeably restricted, which means
that there is greater opportunity for ramp metering to improve the
traffic flow. LOS E describes operation at capacity, with virtually no
usable gaps in the traffic stream, and ramp metering loses its
effectiveness. LOS F describes breakdowns in vehicular flow, resulting
in queues. The benefits of ramp meters are greatest on facilities where
the ability to maneuver is restricted, but not impossible. In this
context, that can be considered equivalent to Level of Service (LOS) C,
or D, as defined in the Highway Capacity Manual.^11^ At LOS A and B,
there is typically not enough volume for ramp metering to be beneficial,
while at LOS E and F, congestion is too severe to be mitigated by ramp
metering alone.

Table 1.1 summarizes the average benefits derived from ramp meter
implementation and also shows the range of benefits cited in a number of
published studies.

**Table 1.1: Ramp Meter Benefits^6^**

  ------------------------------ -------------------- --------------------
  **Measure of Effectiveness**   **Average            **Range of
                                 Improvement**        Improvement**

  Travel Time                    22%                  7% to 91%

  Reduced Collisions             29%                  5% to 50%

  Increased Throughput           38%                  0% to 86%

  Improved Travel Time           Not Quantified       Not Quantified
  Reliability                                         
  ------------------------------ -------------------- --------------------

The following sections explain how ramp meters achieve these benefits.

### 1.4.1 Temporal Shift of Demand {#temporal-shift-of-demand .unnumbered}

A temporal shift in demand is a shift of travel demand in time. For
example, motorists may shift a trip made for convenience such as a
shopping trip to off-peak hours. Delays imposed at freeway entrances by
ramp meters have the effect of deferring the time of arrival to
downstream bottlenecks and to the merge area. The temporal shifts caused
by the use of ramp meters delay the onset of congestion, by helping to
reduce the likelihood that demand exceeds capacity at critical
bottlenecks. This strategy can be deployed as a point treatment to ease
congestion in a busy merge area or on a systemwide basis using multiple
meters to limit the volume at a bottleneck many miles downstream.

Excessive demand at entrance ramps is also caused by common work hours.
For example, many workers leave work at 5 PM, creating a five to fifteen
minute surge in traffic that exceeds the capacity of the facility. Often
times, this results in congestion and breakdown of the facility. Ramp
metering can cause a temporal shift in demand when discretionary trips
are avoided during the peak periods. In some major cities, commuter
trips are also shifted to outside the peak period, when freeway users
elect to defer their trips outside the peak periods by working flextime,
exercising or dining near work.

### 1.4.2 Spatial Shift of Demand  {#spatial-shift-of-demand .unnumbered}

Spatial demand shift occurs when freeway users elect to use alternative
routes. The most common shift is to a downstream ramp that is less
congested, thus reducing the variability in ramp usage. For example,
before metering is implemented the upstream ramp may have a volume of
1,200 vph and the downstream ramp may have a volume of 300 vph. After an
appropriate metering plan is implemented, each ramp is likely to have a
volume much closer to 750 vph. In addition, metering will have a
tendency to divert short trips from the freeway to arterials. When the
meter is on, the delay motorists incur at the ramp meter is matched or
exceeded by travel time savings on the freeway itself. The level of
benefit is related to trip length. Motorists with long trips will find
that the wait at the meter is worthwhile. Others with shorter trips,
typically three or fewer miles in length, often find that completing the
trip entirely on surface streets is faster. A careful balance must be
struck between freeway congestion management using ramp meters and
surface street traffic impacts that may affect the livability of
communities located near the alternate routes.

### 1.4.3 Modal Shift {#modal-shift .unnumbered}

Theoretically, it is feasible to shift demand from the single-occupant
vehicle (SOV) to transit or other high occupancy vehicles (HOV) when
preferential treatment is given to these types of vehicles. In ramp
metering, preferential HOV treatment is achieved through the use of
special HOV bypass lanes to avoid queues at metered ramp sites. In order
for these programs to be effective, adequate transit and ridesharing
opportunities must be available. In addition, adequate enforcement of
HOV bypass facilities must be provided to avoid SOV usage of these
facilities.

### 1.4.4 Collision Reduction {#collision-reduction .unnumbered}

Ramp metering tends to reduce the number and severity of rear-end
collisions on the mainline, because the acceleration and deceleration
patterns of stop-and-go driving are reduced. In addition, the frequency
of sideswipe collisions in the merge area are reduced, because of
reduced side friction and the availability of gaps to allow the merging
of a single vehicle rather than a platoon of vehicles.

## 1.5 Drawbacks of Ramp Meters {#drawbacks-of-ramp-meters .unnumbered}

Some of the potential drawbacks of ramp meters are listed below:

1.  Ramp meters encourage motorists on short trips to divert to surface
    streets, potentially increasing congestion on surface streets.

2.  Ramp queues may impact the operation of adjacent surface streets.

3.  Ramp meters may be perceived as ineffective because the delays they
    impose to motorists are easily perceived, while the delays they
    eliminate or reduce are harder to observe.

4.  Ramp meters may result in an increase in low-speed rear-end
    collisions on the on-ramp due to ramp meter signalization.

##  {#section-1 .unnumbered}

## 1.6 Application of Recommendations {#application-of-recommendations .unnumbered}

The design advice and typical designs presented in this guidelines
document should not be directly applied to ramp meter retrofit projects
without giving consideration to customizing the geometric design
features to meet site and traffic conditions of the ramp and mainline
including:

1.  Roadway Geometry

2.  Design Volume

3.  Design Speeds

4.  Collision Patterns

5.  HOV Volumes

It is also important to consider conducting overall interchange traffic
flow analysis such as highway capacity and specific traffic signal
operation analysis, including phasing and timing splits as they relate
to traffic queues on the on-ramps.

These guidelines do not cover every aspect of every ramp meter
application that may arise on ADOT freeways. Sound engineering judgment
is required for implementation of the design guidelines in this
document. All ramp meter retrofit designs should be reviewed by ADOT
Traffic Engineering on a case-by-case basis.

When feasible, it is desirable to exceed the minimums presented.

# **Ramp Meter Warrants**

This chapter presents a systematic methodology for determining whether
ramp metering is warranted. The installation of ramp control signals
should be preceded by an engineering study of the physical and traffic
conditions on the highway facilities likely to be affected.

##  {#section-2 .unnumbered}

## 2.1 Purpose of Warrant Process {#purpose-of-warrant-process .unnumbered}

The purpose of the warrant process is to have a common, formal procedure
in place that can be applied in a variety of candidate ramp metering
cases to determine whether ramp meter deployment is appropriate. A
number of individual warrants are considered, some of which are
subjective and qualitative, while others are more objective and
quantifiable. The overall warrant process incorporates these individual
warrants in a process that balances both the qualitative and
quantitative conditions of a candidate ramp meter location.

The warrant process can be applied to ramps that are being considered
for ramp metering, as well as for existing metered ramps that are being
considered for modification or removal of existing metering.

## 2.2 Geographic Scope of Study {#geographic-scope-of-study .unnumbered}

The study should include the ramps, ramp connections, and surface
streets that would be affected by the ramp control, as well as the
freeway section concerned.

## 2.3 Data Requirements {#data-requirements .unnumbered}

The following traffic data should be collected:

1.  Current traffic volumes, for both the mainline and ramp

2.  Future traffic volumes for design year, for both the mainline and
    ramp

3.  Collision data, for both the mainline and ramp

4.  Freeway and ramp operating speeds

Either current or future volumes can be used in the warranting process,
depending on the availability of data and the nature of the application
being considered. Current volumes should be collected at a maximum of
fifteen-minute time increments.

## Individual Warrants

The following are the individual warrants that are used to determine if
ramp metering is warranted for a particular ramp. The results of these
individual warrants are analyzed by the overall warrant process to
determine if ramp metering is warranted at a particular ramp location.

### 2.4.1 Warrant One -- Recurring Congestion Warrant^7^ {#warrant-one-recurring-congestion-warrant7 .unnumbered}

Does the freeway operate at speeds less than 50 mph for a duration of at
least 30 minutes for 200 or more calendar days per year?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.2 Warrant Two -- Collision History Pattern^7^ {#warrant-two-collision-history-pattern7 .unnumbered}

Is there a high frequency of crashes (collision rate along the freeway
exceeds mean collision rate in the subject metropolitan area) near the
freeway entrances because of inadequate merge area and congestion?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.3 Warrant Three -- Freeway Level of Service^7^ {#warrant-three-freeway-level-of-service7 .unnumbered}

Will the ramp meter or system of ramp meters contribute to maintaining a
specific level of service (LOS) identified in the region's
transportation system management (TSM) plan?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.4 Warrant Four -- Modal Shift^7^ {#warrant-four-modal-shift7 .unnumbered}

Will the ramp meter or system of ramp meters contribute to maintaining a
higher level of vehicle occupancy through the use of HOV preferential
treatments as identified in the region's transportation system
management (TSM) plan?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.5 Warrant Five -- Redistribution of Access^7^ {#warrant-five-redistribution-of-access7 .unnumbered}

Will the ramp meter or system of ramp meters contribute to balancing
demand and capacity at a system of adjacent ramps entering the same
facility?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.6 Warrant Six -- Sporadic Congestion Warrant^7^ {#warrant-six-sporadic-congestion-warrant7 .unnumbered}

Does the ramp meter or system of ramp meters mitigate predictable
sporadic congestion on isolated sections of freeway because of short
peak period loads from special events or from severe peak loads of
recreational traffic?

**\_\_\_\_ Yes \_\_\_\_ No**

##  {#section-3 .unnumbered}

### 2.4.7 Warrant Seven: Total Volume Warrant^9^ {#warrant-seven-total-volume-warrant9 .unnumbered}

**Table 2.1: Total Volume Warrant Criteria**

+-----------------------------------+-----------------------------------+
| **Number of Mainline Lanes in One | **Criteria Volume**               |
| Direction including Auxiliary     |                                   |
| Lanes that Continue at least 1/3  | **Ramp Plus Mainline Volume       |
| Mile downstream from Ramp Gore**  | Downstream of Gore (total vph)**  |
+-----------------------------------+-----------------------------------+
| 2                                 | 2,650                             |
+-----------------------------------+-----------------------------------+
| 3                                 | 4,250                             |
+-----------------------------------+-----------------------------------+
| 4                                 | 5,850                             |
+-----------------------------------+-----------------------------------+
| 5                                 | 7,450                             |
+-----------------------------------+-----------------------------------+
| 6                                 | 9,050                             |
+-----------------------------------+-----------------------------------+

This warrant is met when the criteria in Table 2.1 is satisfied. Is the
ramp plus mainline volume greater than the tabulated criteria for the
design hour?

**\_\_\_\_ Yes \_\_\_\_ No**

### 2.4.8 Warrant Eight: Right Lane plus Ramp Volume Warrant^9^ {#warrant-eight-right-lane-plus-ramp-volume-warrant9 .unnumbered}

Ramp metering is warranted when the volume of the ramp plus the mainline
right lane exceeds 2,100 vph. Is the criteria defined above met, during
the design hour?

\_\_\_\_ Yes \_\_\_\_ No

### 2.4.9 Warrant Nine: Geometric Warrant^9^ {#warrant-nine-geometric-warrant9 .unnumbered}

Do the existing or proposed ramp geometry permit safe and effective ramp
metering?

\_\_\_\_ Yes \_\_\_\_ No

At some locations, steep inclines on a ramp may warrant against
implementing ramp metering at that location. Available lane widths may
also be inadequate for metering.

## 2.5 Overall Ramp Metering Warrant {#overall-ramp-metering-warrant .unnumbered}

Follow the steps below to determine whether ramp metering is warranted.

1.  Are any of Warrants One, Two, Three, Four, Five, or Six satisfied?
    If yes to any, go to Step 2. If no to all, STOP -- ramp metering is
    not warranted.

2.  Are either Warrants Seven or Eight satisfied? If yes to either, go
    to Step 3. If no to both, STOP -- ramp metering is not warranted.

3.  An exception to the two previous criteria is that ramp metering may
    be warranted solely due to current or anticipated high collision
    rates at a location. Therefore, in some cases at the discretion of
    ADOT, if Warrant 2 is satisfied, ramp metering can be warranted even
    if Warrants Seven and Eight are both not satisfied.

4.  Is Warrant Nine satisfied? If yes, ramp metering is warranted. If
    no, STOP -- ramp metering is not warranted.

Exhibit 2.1 illustrates the warrant analysis procedure in flowchart
format.

##  {#section-4 .unnumbered}

## 2.6 Warrant Analysis Example {#warrant-analysis-example .unnumbered}

The following example shows how the warrant analysis process can be
followed for a hypothetical ramp meter warrant case.

In this example, assume that the following conditions exist at a
candidate ramp meter site:

-   Four lanes of mainline traffic

-   Total mainline peak hour volume of 6400 vph

-   Right Lane plus ramp volume of 1700 vph

-   Statistically above-average collision rates at ramp entrance

-   No existing HOV or transit facilities

-   Agency desires to improve LOS

-   Even distribution of demand and capacity at adjacent on-ramps

-   No significant special event or sporadic congestion

-   Mainline speed is maintained at 50 mph throughout the day for the
    majority of days

-   Adequate geometry for safe and effective ramp metering

Based on the above example conditions, the following results can be
observed for the individual and overall warrants. We can see from the
warrant analysis that ramp metering is warranted in this case.

**Individual Warrants**

**Overall Warrant Step One:** Are any of Warrants

One, Two, Three, Four, Five, or Six satisfied?

**YES,** Continue

**Overall Warrant Step Two:** Are either Warrants

Seven or Eight satisfied? **YES,** Continue

Exhibit 2.1 Ramp Meter Warrant Flowchart

# **Ramp Meter Design**

## 3.1 Introduction {#introduction-1 .unnumbered}

This chapter discusses ramp meter design. The initial sections focus on
selecting the design hour volumes and selecting the number or lanes that
should be metered based on volume criteria. Later sections in this
chapter discuss design guidelines applicable to all ramp meters.
Finally, specific details for specific ramp configurations, such as one
lane, two lane and retrofit applications are discussed.

##  {#section-5 .unnumbered}

## 3.2 Design Volume {#design-volume .unnumbered}

This section lists the design volume criteria for new ramp meter
installations and retrofit applications.

1.  Geometric design of new facilities should be based on future
    peak-hour traffic volumes 20 years after completion of the
    construction.^4^

2.  Geometric design of operational improvements such as ramp meter
    conversions (e.g., one-lane ramp meter to two-lane ramp meter)
    should be based on future volumes, if such projected volumes are
    available, and if right-of-way and geometric constraints allow. At a
    minimum, ramp meter conversions should be based on current volumes.
    ^4^

## 3.3 Choosing the Number of Lanes to Meter {#choosing-the-number-of-lanes-to-meter .unnumbered}

The future peak hour volume should be used to determine the number of
lanes that a ramp meter requires for basic operation. Queue storage
capacity is another determining factor for the number of lanes to be
provided, as discussed later in this Chapter. Table 3.1 provides
guidance on the number of lanes to meter based on design hour volume.

**Table 3.1: Recommended Number of Lanes^8^**

  ----------------------------------- -----------------------------------
  **Ramp Volume (RV, vph)**           **Ramp Treatment**

  180 \< RV \< 500                    Single Lane Ramp Meter

  500 \< RV \< 900                    Consider Two Lane Ramp Meter for
                                      Queue Storage

  900 \< RV \< 1,350                  Two Lane Meter

  RV \> 1,350                         Two Lane Meter; and consider adding
                                      an additional freeway lane and
                                      recheck warrants
  ----------------------------------- -----------------------------------

In addition to peak hour volumes, roadway lane geometry should be a
factor in the number of metered lanes. In some cases, dual left or right
turn lanes from the surface to the ramp may suggest the use of dual lane
metering.

## 3.4 Freeway Entrance Types {#freeway-entrance-types .unnumbered}

Two common types of entrance ramp treatments are provided to allow
drivers entering a highway to accelerate until the desired highway speed
is reached. The taper type provides for a direct entry onto the freeway
at a flat angle. The parallel type of entrance provides an acceleration
lane to meet the highway operating speed. See Exhibit 3.1.

The following discussion does not cover all of the freeway entrance
types that may be encountered during ramp meter design, but rather is
meant as a general guide. Situations such as auxiliary lanes, add lanes,
freeway-to-freeway ramps, horizontal and vertical curves of the
mainline, and various other situation are not discussed here, but can be
referenced in various other ADOT design documents.

### 3.4.1 Taper Type Entrances {#taper-type-entrances .unnumbered}

A taper type entrance will operate smoothly at all volumes up to and
including the design capacity of the merging area. By relatively minor
speed adjustments, the entering driver can see and use any available gap
in the through-traffic stream. The entrance is merged onto the freeway
with a long uniform taper. The desired taper rate is 50:1 to 70:1
between the outer edge of the acceleration lane and the edge of the
through traffic lane. The gap acceptance length should also be
considered in a taper type of design.

The geometrics of the ramp should be such that the motorists can attain
a speed that is within 15 miles per hour of the operating speed by the
time they reach the point where the left edge of the ramp joins the
traveled way of the freeway. This point is known as the point of
convergence and is often assumed to be the point where the right stripe
of the ramp is offset 12 feet from the right stripe of the mainline.

Ramp length for a taper type entrance should be based on the longer of
the:

1.  Gap Acceptance Length (L~g~)

2.  Acceleration Length (L~a~)

#### 3.4.1.1 Gap Acceptance Length  {#gap-acceptance-length .unnumbered}

The gap acceptance length is the distance from the nose of the ramp to
the point of convergence. Typical ramp nose widths are 2 feet to 10
feet. (See Exhibit 3.1) Minimum gap acceptance length should be in the
range of 300 to 500 feet depending on nose width.

![](media/image1.png){width="7.477777777777778in"
height="9.622222222222222in"}

#### 3.4.1.2 Acceleration Distance {#acceleration-distance .unnumbered}

The distance needed for acceleration in advance of the point of
convergence is determined by the difference between the operating speed
on the ramp and the operating speed of the highway. For a ramp meter,
the acceleration length will begin at the stop bar and end at the point
of convergence. Table 3.2 shows recommended acceleration lengths from
the stop bar to the point of convergence for various design speeds for
grades up to 2%.

**Table 3.2: Acceleration Length^1^**

  ----------------------- ----------------------- -----------------------
  **Highway Design Speed  **Speed Reached V~a~    **Acceleration Length
  V (mph)**               (mph)**                 L~a~ (feet)**

  50                      39                      720

  55                      43                      960

  60                      47                      1,200\*

  65                      50                      1,410\*

  70                      53                      1,620\*

  75                      55                      1,790\*
  ----------------------- ----------------------- -----------------------

\* Increase taper from 50:1 to 70:1 when feasible.

When truck volumes of three or more axle trucks exceed 5% on entrance
ramps to freeways with sustained grades exceeding 3% a minimum of 500
feet of additional acceleration area should be provided beyond the ramp
convergence point.

### 3.4.2 Parallel Type Entrances {#parallel-type-entrances .unnumbered}

A parallel type of entrance design provides for an additional lane to
enable a vehicle to accelerate to freeway speed before merging. The
driving maneuver to enter the freeway is similar to a lane change to the
left. Parallel entrances provide operational and safety benefits because
more time is provided for merging vehicles to find a gap.

A taper is provided at the end of the added lane. A taper length of 300
feet is suitable for design speeds up to 70 miles per hour.^1^ The
length of a parallel acceleration lane is measured from the point where
the left edge of the traveled way of the ramp joins the traveled way of
the freeway to the beginning of the downstream taper.

A horizontal curve with a radius of 1,000 feet and a length of 200 feet
should be provided in advance of the lane, if possible.^1^ If the curve
radius is too short, undesirable merging operations will result from
motorists driving directly onto the freeway without using the
acceleration lane.

Recommendations for ramp entrances using the parallel end treatment are
summarized below.

1.  Provide an acceleration length based on the design speed. (See Table
    3.2)

2.  Provide an acceleration length not less than 1,200 feet when it is
    anticipated that the merge will frequently carry volumes approaching
    capacity.

3.  Provide a 200-foot-long horizontal curve with a 1,000-foot radius
    upstream of the acceleration lane.

4.  Provide a tapered end treatment a minimum of 300 feet long, to
    terminate the acceleration lane. The taper should be preceded by a
    full width lane length of at least twice the length of the taper.

### 3.4.3 Design Guidelines Choosing Entrance Types {#design-guidelines-choosing-entrance-types .unnumbered}

ADOT's established design criteria for selecting tapered versus parallel
entrance types are summarized below.^13^

1.  All new or reconstructed entrance ramps in the urban and "urban
    fringe" areas of metropolitan Phoenix and Tucson shall be
    constructed as parallel type entrance ramps.

2.  Entrance ramps in other urban areas such as Yuma and Flagstaff
    should be evaluated on a case-by-case basis for parallel or tapered
    type entrance design.

## 3.5 Design Guidelines for Placement of Stop Bars {#design-guidelines-for-placement-of-stop-bars .unnumbered}

This section summarizes design policies for the placement of ramp stop
bars. Another term sometimes used for the stop bar is limit-line.

1.  The stop bar location should be determined based by the selected
    transition taper, and the required acceleration length.

2.  The stop bar should be located a minimum of 75 feet upstream from
    the point where the ramp gore is 23 feet wide.

3.  Use a single 18-inch-wide white line for the stop bar.

4.  Do not use staggered stop bars on multi-lane ramps.

## 3.6 Design Guidelines for Queue Storage {#design-guidelines-for-queue-storage .unnumbered}

##  {#section-6 .unnumbered}

This section provides design guidelines for selecting appropriate queue
storage lengths for ramp meters.

1.  The necessary storage is highly impacted by the operation of the
    interchange traffic signal depending on the overall traffic turning
    movements. If the cycle length is too long, the queues on on-ramps
    are likely to be longer too. Therefore, ramp meter queue storage
    should be coordinated with entire interchange traffic signalization.

2.  Adequate storage lengths for queues should be provided for all ramp
    meter installations.

3.  A two-lane storage area should be considered for ramps having a peak
    hour volume between 500 and 900 vph. A two-lane storage area should
    be provided for all ramps with peak hour volume greater than 900
    vph.

4.  To minimize the impact on local street operations, ramp meter
    storage should be contained on the ramp whenever possible.

5.  The storage length that can be provided on the ramp itself may be
    limited by downstream weaving and merging distance requirements and
    right-of way constraints.

6.  If the storage area cannot be provided on the ramp by widening or
    lengthening, improvements to the local street system near the ramp
    should be considered to provide the required storage.

7.  The current peak period of 5 or 15-minute arrival rates and
    anticipated or current ramp meter discharge rates should be used to
    calculate the required storage length.

8.  A vehicle spacing of 30 feet from front of vehicle to front of
    vehicle is recommended for designing storage on metered ramps.

9.  Additional spacing should be provided at locations where there are a
    significant percentage of long vehicles such as trucks, buses, or
    recreational vehicles.

The metering rate and demand are major factors in determining the
required queue storage length. Metering rates are discussed under the
Ramp Meter Operation chapter of this document.

## 3.7 Design Guidelines for the Removal of HOV Preferential Lanes {#design-guidelines-for-the-removal-of-hov-preferential-lanes .unnumbered}

The following points should be considered regarding the removal of HOV
preferential bypass lanes.

1.  The removal of HOV preferential treatments should be considered as a
    part of every ramp meter modification project, especially if
    violation rates are greater than 50%.

2.  HOV preferential lanes should be removed if pavement delineation and
    signing cannot provide adequate guidance to direct SOVs to safely
    enter or merge into the SOV lane.

3.  HOV lanes should be removed if roadway geometrics could cause an SOV
    to become inadvertently trapped in the HOV lanes. A common example
    would be dual left turn lanes entering a freeway ramp.

4.  HOV lanes should be removed if HOV and SOV utilization is unbalanced
    and the storage area of both lanes is needed for general-purpose
    ramp queue storage.

5.  HOV lanes should be removed if a direct access HOV drop ramp is
    available within 1.25 miles of the proposed HOV lane.^4^ An HOV drop
    ramp, is a dedicated freeway ramp serving a freeway HOV lane,
    without the need to merge across multiple general purpose lanes to
    enter the freeway HOV lane.

6.  HOV lanes should be removed if high collision rates due to the
    existing ramp metering are shown to be significant.

7.  All lane drops should be designed in accordance with existing ADOT
    standards.

## 3.8 Design Guidelines for the Installation of HOV Preferential Lanes for Ramps {#design-guidelines-for-the-installation-of-hov-preferential-lanes-for-ramps .unnumbered}

The following points should be considered regarding the installation of
HOV preferential bypass lanes.

1.  HOV preferential ramp meter lanes should be considered only in
    locations with mainline HOV lanes or transit facilities.

2.  HOV preferential ramp meter lanes should only be considered for
    locations that have concurrence from DPS to provide adequate
    enforcement.

3.  The HOV preferential lane should be located on the right side, if
    present.

4.  Specific HOV lane treatments must be tailored to the unique
    conditions at each ramp location.

5.  HOV preferential lanes should not be installed when pavement
    delineation and signing cannot provide adequate guidance to direct
    SOVs to safely enter or merge into the SOV lane.

6.  HOV lanes should not be installed when roadway geometrics could
    cause an SOV to become inadvertently trapped in the HOV lanes. A
    common example would be dual left turn lanes entering a freeway
    ramp.

7.  HOV lanes should not be installed when the storage area of both
    lanes is needed for general-purpose ramp queue storage.

8.  HOV lanes should not be installed when a direct access HOV drop ramp
    is available within 1.25 miles of the proposed HOV lane. An HOV drop
    ramp, is a dedicated freeway ramp serving a freeway HOV lane,
    without the need to merge across multiple general-purpose lanes to
    enter the freeway HOV lane.

9.  When HOV lanes are initially implemented, they should be implemented
    with the understanding that the HOV lane may be used as a second
    metered lane in the future.

## 3.9 Design Guidelines for Ramp Meter Enforcement Areas {#design-guidelines-for-ramp-meter-enforcement-areas .unnumbered}

The following guidelines provide design recommendations for ramp meter
enforcement areas. Enforcement area details should be reviewed by DPS
during the site design process.

1.  The enforcement area is not required for a single lane meter, since
    the probability of violation is low; however:

2.  Provision for a future enforcement area should be considered for all
    new ramp meter installations, if geometric constraints allow.

3.  Paved enforcement areas for two-lane ramp meters should be
    considered when possible.

4.  An enforcement area should be considered on ramps having HOV
    preferential treatments.

5.  When all lanes of the ramp are metered, the enforcement area should
    begin as close to the ramp meter stop bar as practical, without
    creating a geometric situation that would allow vehicles to queue up
    in the enforcement area.

6.  Where unmetered HOV bypass facilities exist, the enforcement area
    should begin 150 to 175 feet downstream of the ramp meter stop bar.

7.  Enforcement areas should be 15 feet wide, when feasible.

8.  Enforcement areas should begin with a 30 foot long taper when
    possible.

9.  Enforcement areas should be 75 to 100 feet long.

10. Enforcement areas should taper back into the shoulder with a taper
    in the range of 10:1 to 15:1, to allow enforcement vehicles to
    safely merge into traffic.

11. Enforcement area dimensions may be customized to fit site
    conditions.

Figure 3.2 illustrates a typical enforcement area.

The decision of whether or not to implement an enforcement area is
dependent upon the specific ramp meter site. Coordinate all enforcement
area implementation with the ADOT Project Manager.

## ![](media/image2.png){width="7.397916666666666in" height="9.625in"} {#section-7 .unnumbered}

## 3.10 Single Lane Metered Ramp Design {#single-lane-metered-ramp-design .unnumbered}

This section presents recommended guidelines for single lane metered
ramps.

Single lane entrance ramps may be designed for volumes of up to 900 vph.

###  {#section-8 .unnumbered}

This section summarizes the recommended horizontal alignment features
for one lane metered ramps. Exhibit 3.3 depicts a typical one lane
metered ramp.

1.  Recommended pavement widths for single lane entrance ramps are as
    follows.

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  One Lane Metered  12 Feet           2 Feet            8 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

2.  Recommended minimum pavement widths for single lane entrance ramps
    at locations that may be a future two lane ramp are as follows.

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  One Lane Metered  12 Feet           8 Feet            8 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

3.  Additional pavement width should be provided when the radius of the
    ramp is less than 300 feet.

4.  When paved shoulders are provided on ramps, they should have a
    uniform width.

5.  Ramps should have a lateral clearance to any barrier or fixed object
    on the right outside edge of the traveled way of at least six feet,
    as measured from the edge of traveled way to closest portion of the
    barrier or fixed object. Eight to ten feet is preferred.

6.  Ramps should have a lateral clearance to any barrier or fixed object
    on the left outside edge of the traveled way of at least four feet,
    as measured from the edge of traveled way to closest portion of the
    barrier or fixed object.

7.  The lateral clearance to any barrier or fixed object must never be
    less than two feet.^1^

8.  Ramps should be designed without barrier curbs.

## ![](media/image3.png){width="7.416666666666667in" height="9.625in"} {#section-9 .unnumbered}

## 3.11 Dual Lane Metered Ramps {#dual-lane-metered-ramps .unnumbered}

##  {#section-10 .unnumbered}

The following volume and storage criteria apply to dual lane metered
ramps:

1.  Dual lane metered ramps should be considered when volumes reach 500
    to 600 vph and a single lane will provide insufficient storage.

2.  Dual lane ramp meters are highly recommended when the ramp volume
    exceeds 900 vph.

3.  When ramp volumes reach 1,350 vehicles per hour, an additional
    freeway lane should be considered downstream of the ramp meter.

4\. Dual lane entrance ramps may be designed for volumes of up to 1,800
vph.

5.  Consider upgrading to a two-lane ramp meter when insufficient
    storage space is provided by a single lane ramp meter, or when
    drivers queue up two cars across in a single lane at the stop bar.

The guidelines below describe the recommended features for dual lane
entrance ramps.

1.  Acceleration distance requirements for dual lane ramp meters are
    generally the same as single lane ramp meters.

2.  When upgrades exceed 2 percent and the volume of 3 axle trucks
    entering the freeway exceeds 5%, a dual lane acceleration area
    should be considered, to allow passenger cars to pass heavy
    vehicles.

3.  As with a single lane ramp, when truck volumes of 3 or more axle
    trucks exceed five percent on entrance ramps to freeways with
    sustained grades exceeding 3% a minimum of 500 feet of additional
    acceleration area should be provided beyond the ramp convergence
    point.

4.  When ramp volumes exceed 1,350 vph, a 1,000 foot auxiliary lane or
    add lane should be provided beyond the ramp convergence point.

5.  Recommended minimum pavement widths for dual lane entrance ramps
    [without]{.underline} right-of-way constraints are as follows:

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  Two Lane Metered  24 Feet           2 Feet            2 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

6.  Recommended minimum pavement widths for dual lane entrance ramps
    [with]{.underline} right-of-way constraints or on structures are as
    follows:

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  Two Lane Metered  22 Feet           2 Feet            2 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

> If minimum pavement widths cannot be satisfied, ADOT Roadway
> Engineering must approve the design on an individual basis.

7.  On loop ramps having a radius of 300 feet or less, consider widening
    the right lane to accommodate design vehicle off-tracking, where the
    curvature of the horizontal curvature of the ramp causes the rear
    wheels of the vehicle to track outside the lane striping.

8.  The multi-lane segment should transition to a single lane width
    between the ramp meter limit line and the point where the 6 foot
    separation point between the left edge of the ramp and the right
    edge of the mainline traveled way.

9.  Lane drop transitions should be accomplished with a taper of 50:1.

10. A lesser taper may be warranted by specific site conditions. As an
    example loop ramps will normally not allow traffic to reach speeds
    to warrant a 50:1 taper.

11. When the design speed of the ramp is 50 mph or less, the lane drop
    should be accomplished with a taper in the range of 30:1 to 50:1.

12. The lane drop taper must never be less than 15:1 regardless of site
    conditions.^1^

13. Before the start of the taper, there should be an adequate tangent
    distance to accommodate high ramp speeds when the ramp meter is not
    in operation.

14. When paved shoulders are provided on ramps, they should have a
    uniform width.

15. Ramps should have a lateral clearance to any barrier or fixed object
    on the right outside edge of the traveled way of at least six feet,
    as measured from the edge of traveled way to closest portion of the
    barrier or fixed object. Eight to ten feet is preferred.

16. Ramps should have a lateral clearance to any barrier or fixed object
    on the left outside edge of the traveled way of at least four feet,
    as measured from the edge of traveled way to closest portion of the
    barrier or fixed object.

17. The lateral clearance to any barrier or fixed object must never be
    less than two feet, as measured from the edge of traveled way to
    closest portion of the barrier or fixed object.

18. Ramps should be designed without barrier curbs.

Exhibit 3.4 illustrates a typical dual lane metered ramp.

## 3.12 Ramp Meter Retrofit Applications {#ramp-meter-retrofit-applications .unnumbered}

Ramp meter retrofit applications are special cases of one and two lane
ramp meter designs. Generally, existing conditions will require some
deviation from the ideal design criteria described above. The minimum
design criteria presented in this guideline should be met for all
applications including the retrofit application, where practical.

##  {#section-11 .unnumbered}

Geometric design for ramp meter retrofit applications should be based on
current peak-hour traffic volume. If traffic data less than two years
old is not available at the time of the design, data should be collected
before proceeding with the design.

### 3.12.1 One-Lane Ramp Meter to Two-Lane Ramp Meter Conversion {#one-lane-ramp-meter-to-two-lane-ramp-meter-conversion .unnumbered}

This section describes some design criteria for conversion of ramp
meters from one lane to two lane configurations. The work to convert a
ramp meter from one lane to two lanes is often minor striping, signing
and electrical work. See Exhibit 3.5.

1.  Recommended minimum pavement widths for dual lane entrance ramps
    [without]{.underline} right-of-way constraints are as follows.

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  Two Lane Metered  24 Feet           4 Feet            8 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

![](media/image4.png){width="7.481944444444444in"
height="9.627777777777778in"}

![](media/image5.png){width="7.444444444444445in" height="9.625in"}

2.  Recommended minimum pavement widths for dual lane entrance ramps
    [with]{.underline} right-of-way constraints or on structures are as
    follows.

  ----------------- ----------------- ----------------- -----------------
  **Description**   **Traveled Way**  **Inside          **Outside
                                      Shoulder**        Shoulder**

  Two Lane Metered  22 Feet           2 Feet            2 Feet
  Ramp                                                  
  ----------------- ----------------- ----------------- -----------------

3.  Avoid placing shoulder striping in gutters or other drainage areas.

4.  Never use tapers less than 30:1 for ramps having design speeds
    greater than 50 mph.

5.  Never use tapers less than 15:1 for ramps having design speeds less
    than or equal to 50 mph.

### 3.12.2 One-Lane + HOV Conversion to Two-Lane Ramp Meter {#one-lane-hov-conversion-to-two-lane-ramp-meter .unnumbered}

Conversion of a one lane + HOV ramp meter to a two lane ramp meter
should be subject to the following guidelines:

1.  Continued operation of existing HOV bypass lanes should be
    considered near transit centers that generate a significant transit
    usage (such as Park and Ride facilities).

2.  Removal of HOV preferential lanes should be considered if a history
    of inadequate enforcement that cannot be corrected exists.

3.  Removal of HOV preferential bypasses should be considered when
    adequate pavement delineation and signing cannot provide adequate
    guidance to direct SOVs to safely enter or merge into the SOV lane.

4.  Removal of HOV preferential bypasses should be considered when
    roadway geometrics could cause an SOV to become inadvertently
    trapped in the HOV lanes. A common example would be dual left turn
    lanes entering a freeway ramp.

5.  Removal of HOV preferential bypasses should be considered when HOV
    and SOV utilization is unbalanced and the storage area of two lanes
    is needed for general purpose ramp queue storage.

6.  Removal of HOV preferential bypasses should be considered when a
    direct access HOV drop ramp is available within 1.25 miles of the
    proposed HOV lane.

7.  Removal of unmetered HOV preferential bypasses should be considered
    if a collision pattern suggests that high speed unmetered HOV
    vehicles are not safely merging with the low-speed metered vehicles.

The conversion process to convert a single lane plus HOV bypass ramp to
a dual lane metered ramp involves the steps listed below. Exhibit 3.6
shows an example of a conversion.

The following is an appropriate conversion process:

1.  Remove HOV preferential signing.

2.  Remove HOV pavement markings.

3.  Modify stop bar and striping as needed for site conditions.

4.  Add advance warning sign and beacon "Ramp Metered When Flashing" for
    newly metered lane.

5.  Add "One Vehicle Per Green Sign."

6.  Add "Stop Here on Red Sign."

7.  Add "Merge Warning Sign" as needed.

8.  "All Vehicles Must Stop" signs should be placed when converting a
    non-metered HOV bypass to metered operation.

9.  Add ramp meter head and pole for newly metered lane.

10. Upgrade detection as required to match that of two-lane ramp meter.

    ![](media/image6.png){width="7.458333333333333in" height="9.625in"}

## 3.13 Ramp Meter Hardware {#ramp-meter-hardware .unnumbered}

The following sections provide guidance in the selection and placement
of ramp meter hardware, including signals, poles, detectors, and
controller cabinets.

### 3.13.1 Signals {#signals .unnumbered}

Exhibit 3.7: Typical Ramp Meter Signal Pole

![](media/image7.jpeg){width="2.9506944444444443in"
height="4.405555555555556in"}

1.  For a single lane ramp meter, use a Type A pole (per ADOT Standard
    Drawings) on the left side of the ramp, aligned with the stop bar.

2.  For a dual lane metered ramp, use two Type A poles with one pole on
    each side of the ramp, aligned with the stop bar.

3.  Use a breakaway base on the Type A pole unless it is located behind
    barrier or outside the clear zone.

4.  Some sites may require special wall mounting details of ramp meter
    heads, due to space limitations for the installation of separate
    Type A poles.

5.  Type A poles are to be equipped with (See Exhibit 3.8):

    a.  Red & Green 12" LED Signal Head mounted at 10 foot elevation
        facing the ramp traffic 300 ft back from the stop bar.

    b.  A 2" Red LED enforcement indication mounted at 10 foot
        elevation, facing the downstream enforcement area.

    c.  A 30" x 36" "Stop Here on Red (RT) or (LT) R-10-6 Sign using
        black letters on a white background, mounted directly below 12"
        signal head.

    d.  Red & Green 8" LED Signal Head mounted at 4 foot 6" elevation,
        facing vehicles stopped at the stop bar.

    e.  A 2 5/8" by 18" sticky back "One Vehicle Per Green" sign with
        black text on a white background mounted on the signal
        backplate, below the green 8" head.

    f.  A backplate for each signal head.

    g.  A visor for each signal head. Use a tunnel visor with louvers
        when required to shield the view of the ramp meter heads from
        the freeway mainline.

6.  Mast arm poles may be used for two lane metered ramps, when needed
    due to site constraints that restrict the use of Type A poles.

7.  Mast arm poles should be located 40' downstream of the stop bar.

8.  Mast arm poles must be located outside the clear zone or protected
    with barrier.

9.  Mast arm poles are to be equipped with:

    a.  Red & Green 12" LED Signal Heads for each lane.

    b.  The bottom of the lowest signal head or sign mounted on the mast
        arm must be a minimum of 17' above the pavement surface.

    c.  A 2" Red LED enforcement indication mounted on the back of each
        head., facing the downstream enforcement area.

    d.  A 48" x 20" "1 Car Per Green Each Lane" Sign using black letters
        on a white background.

    e.  A backplate and visor for each signal head.

    f.  Use a tunnel visor with louvers when required to shield the view
        of the ramp meter heads from the freeway mainline.

10. Use LED indications for all new ramp heads.

11. Wire each lane's head(s) with a separate five conductor #14 AWG
    cable from the head to the controller.

    ![](media/image8.png){width="7.444444444444445in" height="9.625in"}

### 3.13.2 Beacons {#beacons .unnumbered}

Exhibit 3.9: Typical Flashing Beacon

1.  ![](media/image9.jpeg){width="2.9479166666666665in"
    height="4.336805555555555in"}ADOT's current policy is to use a Type
    A pole on the left side of the ramp, aligned with the advance queue
    detector (AQD).

2.  For a dual lane ramp, use two Type A poles with one pole on each
    side of the ramp, aligned with the AQD detector.

3.  In special situations where stopping sight distance is limited,
    consider alternative placements of the beacon to enhance the safety
    of the ramp meter operation.

4.  In frontage road situations, it may not be feasible to place the
    right side beacon in a position in the optimum position.

5.  In frontage road situations, site-specific situations may require
    placement of the beacon in the gore area between the ramp and
    frontage road, placement of the beacon on a mast arm pole or
    omission of the beacon.

6.  MUTCD stopping sight distance criteria must be used in analyzing
    each situation.

7.  Use a breakaway base on the Type A pole unless it is located behind
    barrier or outside the clear zone.

8.  Some sites may require special wall mounting details of beacons due
    to space limitations for the installation of separate Type A poles.

9.  Type A poles are to be equipped with a flasher assembly (See Exhibit
    3.10).

10. Yellow 12" LED Signal Head mounted at 10 foot elevation facing
    traffic entering the ramp.

11. A 36" x 36" "Ramp Metered When Flashing" W3-4 Sign using black
    letters on a yellow background, with a bottom elevation of 6'6".

12. A backplate and a visor for the flasher head.

13. Use LED indications for all new flasher heads.

14. Wire each lane's flasher head with a separate five conductor #14 AWG
    cable from the head to the controller.

### 3.13.3 Mainline Detectors {#mainline-detectors .unnumbered}

This section provides guidelines on the deployment of mainline
detection.

1.  The freeway mainline detection is for traffic responsive ramp meter
    operation and traffic monitoring purposes.

2.  Any detection technology that can provide accurate volume, occupancy
    and speed information is suitable as a mainline detection
    technology.

3.  Inductive loop detectors are the most common mainline detection
    technology.

4.  Non-intrusive passive acoustic detectors have been used on some of
    the more recent freeway management system installation and retrofit
    projects.

5.  Use of non-intrusive detection should be considered at sites where
    mainline lanes are being shifted from their original position or
    will be shifted in the foreseeable future.

6.  When feasible, use of preformed loops is preferred over the use saw
    cut loops.

7.  Place the mainline detection zones between 10 and 400 feet upstream
    of the nose of the gore.

    ![](media/image10.png){width="7.430555555555555in"
    height="9.63888888888889in"}

8.  The position of the detection zone should be adjusted within the
    range to allow uniform spacing among detector stations.

9.  Typical mainline detector station is 1/3 mile.

10. Never place mainline detector stations less than ¼ mile or greater
    than ½ mile apart.

11. Avoid placing detector stations in lane taper or heavy merging and
    weaving areas.

12. Do not place loops on bridge decks less than 2,000 feet in length.
    For bridge decks over 2,000 feet in length, detection may be
    provided as described in the FMS Design Guidelines.

13. When installing loops avoid lateral pavement joints.

14. Separate upstream and downstream loops by 18 feet leading edge to
    leading edge to form a speed trap of consistent length.

15. When loops are used, use six by six foot squared loops.

16. When lanes are 12 feet wide or wider, offset the loops by two feet
    from the center of the lane towards the shoulder for the outside
    lane.

17. Center loops in any lane that is less than 12 feet wide or that is
    not adjacent to a shoulder.

18. Use a separate lead-in cable for each loop.

19. Identify each mainline loop as 1D, 1U, 2U, etc. Where 1 or 2
    indicates the lane number counting from the right and U or D
    indicate upstream or downstream in the direction of traffic.

### 3.13.4 Ramp Detectors {#ramp-detectors .unnumbered}

The following detectors are to be provided on metered ramps. The
detectors are listed in order as a vehicle would typically encounter
them while traveling down the ramp:^9^

1.  Advance Queue Detector (AQD)

2.  HOV Interrupt (If installed)

3.  Demand (also known as input)

4.  Passage (also known as output)

#### 3.13.4.1 Queue Detector {#queue-detector .unnumbered}

1.  This detector is also known as the Advance Queue Detector (AQD).

2.  The purpose of this detector is to cause the ramp meter to cycle at
    a faster rate when the queue is sufficiently long that a probability
    of queue spillback onto the surface street exists.

3.  For one lane ramps, a 6' wide by 20' long loop ramp is placed at the
    AQD distance. (See #8 below.)

4.  For newly metered two lane ramps a 6' long by 20' wide loop is
    placed across both lanes of the ramp at the AQD distance.

5.  When the width of the traveled way on a two lane metered ramp
    exceeds twenty-eight feet, the width of the AQD loop should be
    increased to 6 foot long by 24 foot wide, to reduce the possibility
    that queued vehicles will not stop on the detector.

6.  When retrofitting a one lane metered ramp with an HOV bypass lane,
    the existing 6 foot wide x 20 foot long loop in the metered lane
    should be supplemented with a 6 x 6 loop in the lane to be converted
    into a metered lane or a new 6 foot long x 20 foot wide loop may be
    cut.

7.  The AQD distance is measured from the trailing edge of the AQD loop
    to the edge of pavement of the cross street.

8.  The AQD distance is derived using a formula based on the design hour
    volume and distance X, which is the length of the ramp between the
    edge of pavement of the cross street and the stop bar.

9.  The following table provides the AQD calculation formula for a
    single lane ramp based on the design hour volume and computes AQD
    for a typical ramp with the distance X=900 feet between the ramp
    stop bar and cross road edge of pavement.

10. Maximum AQD is 300 feet.

11. An AQD calculation formula should be used for ramps that are less
    than 1,200 feet long. For ramps 1,200 feet or greater in length use
    AQD~max~= 300 feet.

12. AQD Calculation Formula

  ------------------- --------------- ------------------ -----------------
  **Design Hour       **AQD Formula** **Formula Result   **Recommended
  Volume (DHV)**                      (based on X=900    AQD~Typ~ (based
                                      ft)**              on X=900 ft)**

  DHV \>1,080         AQD=.39X        351                300 feet

  1080\>DHV\>900      AQD=.34X        306                300 feet

  900\>DHV\>720       AQD=.28X        252                252 feet

  DHV\<720            AQD=.25X        225                225 feet
  ------------------- --------------- ------------------ -----------------

13. For ramps with an X distance of less than 400 feet between the ramp
    stop bar and the edge of the crossroad pavement, an AQD~min~ = 100
    feet may apply.

14. A single lead in is provided from the AQD loop to the controller.

15. When two AQD loops are installed in a retrofit installation, the
    loops should be connected in parallel to a single lead-in.

#### 3.13.4.2 HOV Interrupt {#hov-interrupt .unnumbered}

1.  The purpose of this detector is to provide gaps in the metered
    traffic for vehicles bypassing the queue in the HOV bypass lane.

2.  This detector is only used when a ramp is equipped with an HOV lane.

3.  This detector should be disconnected when a metered One Lane + HOV
    Bypass ramp is converted to a two lane metered ramp.

4.  When the HOV bypass interrupt detector is required, install it in
    the HOV lane 350 feet upstream of the ramp stop bar.

5.  The HOV interrupt loop shall be a single six by six loop with a
    dedicated lead in cable to the controller.

#### 3.13.4.3 Demand Detectors {#demand-detectors .unnumbered}

1.  These detectors are also known as input detectors.

2.  The purpose of these detectors is to sense the presence of vehicle
    demand at the stop bar. This presence is used by the controller
    firmware to determine the signal operation.

3.  These detectors consist of two six by six foot loops centered in
    each metered lane.

4.  Place the leading edge of the loop nearest the stop bar 3 feet
    upstream of the stop bar.

5.  Separate the leading edges of the two loops in each lane by 16 feet.

6.  Connect the two demand detectors in a single lane in parallel and
    provide one detector lead-in cable for each lane's demand detectors.

#### 3.13.4.4 Passage Detector {#passage-detector .unnumbered}

1.  This detector is also known as the output detector.

2.  The purpose of this detector is to terminate the green interval
    after a vehicle clears the stop bar. Upon passage of a vehicle over
    this detector, a new metering cycle starts.

3.  The trailing edge of this detector should be located 6 feet
    downstream of the stop bar.

4.  Use a six by six loop for passage detection in each lane.

5.  For lanes 12 feet or wider, the detector may be centered in the
    lane.

6.  For narrow lanes, offset the detector away from the center of the
    ramp, so that the edge of each loop is 2 foot from the right or the
    left shoulder.

7.  Each passage detector needs a dedicated lead-in cable to the
    controller.

#### 3.13.4.5 Off-Ramp Detectors {#off-ramp-detectors .unnumbered}

1.  This detector does not affect the operation of the ramp meter.

2.  The purpose of this detector is to provide traffic volume and
    occupancy data for the freeway management system. This information
    can then be used for long term planning purposes.

3.  Freeway to freeway connectors should be equipped with off-ramp
    detectors.

4.  This detector consists of one six by six loop per off ramp lane.

5.  This detector is installed downstream of the ramp gore and upstream
    of any area of the ramp that has been widened to accommodate turning
    movements or provide storage.

6.  Each off-ramp detector has a dedicated lead in cable to the closest
    controller cabinet.

### 3.13.5 Cabinet Assembly {#cabinet-assembly .unnumbered}

########  {#section-12 .unnumbered}

This section provides guidelines and information about the ramp meter
cabinet and controller assembly. The first set of guidelines focuses on
the controller location requirements. The remainder of the guidelines
deal with the cabinet equipment.

Exhibit 3.11: Typical 341 Cabinet Assembly

![](media/image11.jpeg){width="2.8333333333333335in" height="4.125in"}

1.  The specific location of a ramp controller cabinet should be
    determined for each specific site.

2.  The preferred location of the controller cabinet is on the right
    side of the ramp.

3.  Safety should be a factor in placing the cabinet.

4.  The cabinet must be placed outside the clear zone, per AASHTO
    Guidelines. This is typically 30 feet from the edge of the mainline
    traveled way or 20 feet from the edge of the ramp traveled way.

5.  When clear zone requirements cannot be met, the cabinet must be
    protected by a barrier such as guardrail or concrete barrier.

6.  The cabinet location should provide a safe work environment for
    people servicing the cabinet.

7.  The cabinet must be placed at least 5 feet away from the barrier to
    allow for deflection of guardrail upon impact and room to work near
    the cabinet.

8.  A maintenance pad should be provided adjacent to the front and rear
    doors of the cabinet.

9.  The slope adjacent to the cabinet base should be 2:1 or flatter.

10. The cabinet should be located a minimum of 20 feet upstream of the
    stop bar, so that the ramp signal heads are visible from the front
    door of the cabinet.

11. The cabinet should be located no further than 540 feet from the
    furthest 6 x 6 loop and no further than 700 feet from the furthest 6
    by 20 foot loop.

#### 3.13.5.1 Foundation Details {#foundation-details .unnumbered}

Typical controller cabinet foundation details are shown in Exhibit 3.12.

Reinforcing steel in cabinet foundations does not serve a structural
purpose and its omission on future ramp metering projects should be
considered.

#### Model 179 Controller

The Model 179 controller unit is used for detector data processing and
ramp metering by ADOT. The Model 179 controller is based on an MC6809
microprocessor. (See Exhibit 3.13) Controller memory resides on a
separate PROM module card. The Model 179 is designed to operate in the
hostile environmental conditions found in Arizona.

####  {#section-13 .unnumbered}

#### 3.13.5.3 Ramp Control Firmware {#ramp-control-firmware .unnumbered}

####  {#section-14 .unnumbered}

Custom ramp control firmware that resides on a Model 412 PROM Module
currently controls all ADOT ramp meters. The firmware was developed for
ADOT by Bi Trans Systems. All firmware functions (except holiday
scheduling) can be controlled using the 179 controller's keyboard and
convenient hexi-decimal memory map.

####  {#section-15 .unnumbered}

#### 3.13.5.4 Non-Volatile Random Access Memory (NVRAM) {#non-volatile-random-access-memory-nvram .unnumbered}

The 179 controller is equipped with NVRAM and battery backup to ensure
that ramp timing parameters are not lost during a power outage. A
battery back-up is also provided to allow the clock and downtime
accumulator to continue to function for an extended period in the event
of a power outage.

![](media/image12.png){width="7.430555555555555in"
height="9.63888888888889in"}

Exhibit 3.13: Model 179 Controller

![](media/image13.jpeg){width="5.9319444444444445in" height="3.2625in"}

#### 3.13.5.6 Communications Port  {#communications-port .unnumbered}

The Model 179 is equipped with an internal slot for installation of a
modem. Some of the controllers installed on FMS Phase I and Phase II
used telephone modems located in this slot. For the newer phases of the
FMS an RS-232 connection is made to the C2 connector to connect a
separate fiber-optic data transceiver. Future ramp metering projects
using fiber-optic communications may use fiber-optic data transceivers
that mount internally in the modem slot of the 179 controller. These
products have recently become available from fiber-optic equipment
manufacturers and have been used in Texas.

The 179 hardware is capable of data transmission at rates from 300 bps
to 19,200 bps. ADOT ramp meters using copper communications lines
communicate at 1200 and 2400 bps. More recent installations using
fiber-optic transceivers operate at a data rate of 9,600 bps.

####  {#section-16 .unnumbered}

#### 3.13.5.7 Inputs and Outputs  {#inputs-and-outputs .unnumbered}

The 179 controller uses a large square military style connector, known
as the C1 connector to handle controller input and outputs. The hardware
supports up to 44 inputs and 56 outputs. (See Exhibit 3.14)

Inputs are used to connect detectors and AC isolators that monitor the
status of controller outputs, which control the beacon and the ramp
meter indications. DC isolators can also be used in detector slots, to
assert a constant call on a detector input. A position in the input file
corresponds to each controller input. The controller cabinet is provided
with two input files. The upper input file is known as the I File and
the lower input file is known as the J File. Each controller input file
features 14 slots that each have an upper and lower input. The table
below shows the common inputs used in the ADOT ramp metering system. The
controller also has inputs to monitor gate positions and special
function outputs, which are not used in the current ADOT ramp metering
system.

Modification of the input file to combine both Queue detectors into slot
three should also be performed.

The controller outputs come from the C1 connector at a logic voltage
level, which is not suitable for switching 120 VAC lamp loads. Model 200
load switches are used to convert logic level voltages into 120 VAC to
power the beacon and a meter on sign, which is typically not used with
ADOT ramp meters.

**Exhibit 3.14: Input File Layout**

  ------- ---------- ---------- ---------- ---------- ------------ ------------ ----------- ------------ ------ --------- --------- --------- --------- ----------
  Input   Slot 1     Slot 2     Slot 3     Slot 4     Slot 5       Slot 6       Slot 7      Slot 8       Slot 9 Slot 10   Slot 11   Slot 12   Slot 13   Slot 14
  File                                                                                                                                                  

  I       Lane 1     Lane 2 Up  Lane 3     Lane 4     Lane 5       Lane 6       Left/Lane 7 Right/Lane 8 Not    Not Used  Not Used  Not Used  Not Used  Not Used
          Upstream   Detector   Upstream   Upstream   Upstream     Upstream     Upstream/   Upstream/    Used                                           
          Detector              Detector   Detector   Detector     Detector     Exit        Exit                                                        
                                                                                Detector    Detector                                                    

          Lane 1     Lane 2     Lane 3     Lane 4     Lane 5       Lane 6       Left/Lane 7 Right/Lane 8 Not    Not Used  Not Used  Not Used  Not Used  Not Used
          Down       Down       Down       Down       Downstream   Downstream   Down        Down Stream/ Used                                           
          Stream     Stream     Stream     Stream     Detector     Detector     Stream/     Exit                                                        
          Detector   Detector   Detector   Detector                             Exit        Detector                                                    
                                                                                Detector                                                                

  J       Left Lane  Left Queue Right Ramp Not Used   Not Used     Not Used     Not Used    Not Used     Not    Left Lane Right     Beacon    Gate Up   Special
          Ramp Input Detector   Output                                                                   Used   Red       Lane Red  Monitor   Monitor   Function
          Detector              Detector                                                                        Monitor   Monitor   Input     Input     Monitor
                                                                                                                                              (Not      Input (Not
                                                                                                                                              Used)     Used)

          Left Lane  Right Ramp Right Ramp Not Used   Not Used     Not Used     Not Used    Not Used     Not    Left Lane Right     Sign      Gate Down Special
          Ramp       Input      Queue                                                                    Used   Green     Lane      Monitor   Monitor   Function
          Output     Detector   Detector                                                                        Monitor   Green     (Not      Input     Monitor
          Detector                                                                                                        Monitor   Used)     (Not      Input (Not
                                                                                                                                              Used)     Used)
  ------- ---------- ---------- ---------- ---------- ------------ ------------ ----------- ------------ ------ --------- --------- --------- --------- ----------

#### Power Distribution Assembly

The power distribution assembly (PDA) #4 houses four switch packs. The
switch packs are assigned to the following functions:

+-----------------------------------+-----------------------------------+
| **Description**                   | **Function**                      |
+-----------------------------------+-----------------------------------+
| Switch Pack \# 1                  | Left Lane Red                     |
|                                   |                                   |
|                                   | Beacon                            |
|                                   |                                   |
|                                   | Left Lane Green                   |
+-----------------------------------+-----------------------------------+
| Switch Pack #2                    | Right Lane Red                    |
|                                   |                                   |
|                                   | Right Lane Green                  |
+-----------------------------------+-----------------------------------+
| Switch Pack \# 3                  | Gate & Sign Control Functions     |
|                                   |                                   |
|                                   | (Not used in Arizona)             |
+-----------------------------------+-----------------------------------+
| Switch Pack \# 4                  | Special Function Outputs (Not     |
|                                   | Used in Arizona)                  |
+-----------------------------------+-----------------------------------+

The power distribution assembly is also equipped with a set of circuit
breakers to protect circuits controlling:

1.  Controller Equipment

2.  Ramp Indications

3.  Ground Fault Circuit Interrupter Protected Convenience Outlets

4.  CCTV Equipment

A Model 204 solid state flasher is provided to flash the beacon. In
addition, a flash transfer relay and Model 208 conflict monitor are
provided. The model 34X cabinets are also equipped with a slide-out
drawer to store documents and hold a notebook computer while working on
the cabinet.

## 3.14 Ramp Meter Pavement Marking {#ramp-meter-pavement-marking .unnumbered}

1.  Use spayed alkylid thermoplastic 0.060" thick for ramp meter
    striping.

2.  Use alkylid thermoplastic 0.090" thick for the stop bar.

3.  The stop bar should be 18" wide and run from edge line to edge line.

4.  The right edge line of the ramp should be a 6" wide solid white
    line.

5.  When the right edge of the ramp is in a frontage road gore area, a
    12" white right edge line should be used.

6.  The center line of a two lane metered ramp should be a 6" wide white
    solid line in areas where lane changing is to be discouraged,
    typically within 250 feet upstream of the stop bar. The remainder of
    center line to the cross street should be a 6" white broken lane
    line.

7.  The center line for a ramp with an HOV bypass lane should be a 6"
    wide white solid line in areas where lane changing is to be
    discouraged, typically a minimum of 250 feet upstream of the stop
    bar. This white solid line may be extended further upstream, based
    on the geometry of the on-ramp near the cross street. The remainder
    of center line to the cross street should be a 6" white broken lane
    line.

8.  The center line of the ramp should end at the ramp meter stop bar.

9.  The left edge line of the ramp should be a 6" solid yellow line from
    the cross street to the ramp meter stop bar.

10. The left edge of the ramp between the ramp meter stop bar and the
    freeway gore should be a 12" solid white gore line.

11. Striping should not be located in gutters. If geometric constraints
    require striping to be placed in gutter, this should be reviewed on
    a case-by-case basis with ADOT Traffic Engineering.

![](media/image14.jpeg){width="4.017361111111111in"
height="2.545138888888889in"}

Exhibit 3.15: Ramp Meter Stop Bar Pavement Markings (HOV Bypass)

## 3.15 Ramp Meter Signing  {#ramp-meter-signing .unnumbered}

Exhibit 3.16: Typical Ramp Meter Sign

![](media/image15.jpeg){width="2.7958333333333334in"
height="4.09375in"}This section describes ramp meter signing design
guidelines. A typical ramp meter sign is shown in Exhibit 3.16.

1.  Ramp meter signing includes the following signs:

    a.  Ramp Metered When Flashing (W3-4)

    b.  One Vehicle per Green (R10-13)

    c.  One Car per Green Each Lane (R89-1)

    d.  Stop Here on Red (R10-6a)

    e.  Right Lane Ends (W4-2R)

    f.  Merging Traffic (W4-1)

    g.  All Vehicles Stop On Red (use for newly metered ramp lanes)

2.  All ramp meter signs should be installed in accordance with the
    MUTCD. In some retrofit situations, geometric constraints may not
    allow this. Any deviation from the MUTCD must be reviewed by ADOT
    Traffic Engineering on a case-by-case basis.

3.  Ramp meter signing should be coordinated with the ramp guide signs
    and appropriate regulatory signs (e.g. Do Not Enter or Wrong Way)

4.  When an HOV bypass is installed appropriate HOV Lane signage must be
    installed:

    a.  Carpools Buses & Motorcycles Only (R-91)

    b.  Right Lane Do Not Stop (R-88) signs should be placed in the
        non-metered lane upstream of the meter.

    c.  Advance HOV signs should be installed on local streets when they
        are striped for mandatory turns into HOV facilities.

## Typical Conduit and Junction Box Layout

Exhibit 3.17 illustrates the typical location of junction boxes and
routing of conduit for a ramp meter site.

![](media/image16.png){width="7.472222222222222in" height="9.625in"}

# **4. Ramp Meter Operation** {#ramp-meter-operation .unnumbered}

The operation of the ADOT ramp meters, which are located in the Phoenix
area, is the responsibility of the Traffic Operations Center (TOC).

## 4.1 Ramp Meter Stand-Alone Local Operation {#ramp-meter-stand-alone-local-operation .unnumbered}

The following is an overview of the stand-alone local operation of an
ADOT ramp meter site when metering is active.

1.  If the ramp meter signals are not operating, then they go through
    "startup" procedures to begin operation. On a single lane ramp,
    startup consists of the meter going from a darkened state to a green
    signal. For startup on dual lane ramps, the left meter gives a green
    signal, while the right meter remains dark. Once the left meter
    gives a red signal, the right meter gives a green signal.

2.  Once the ramp meter signals are in operation, if there are no
    vehicles activating the demand loops, the signal heads give a red
    signal until the maximum red time is reached.

3.  When a vehicle approaches the on-ramp stop bar and passes over the
    demand loop detector, a green signal is displayed.

4.  The vehicle then crosses the ramp meter stop bar and travels over
    the passage detector as it continues down the ramp toward the
    mainline.

5.  As the vehicle passes over the passage detector, the display turns
    red, and the cycle timer is reset. If the maximum green time elapses
    prior to the vehicle passing over the passage detector, then the
    signal will go red, and the cycle timer is reset.

6.  The signal remains red until another call is placed by the demand
    detector, or until the maximum red time is reached, at which point
    the signal displays a green.

The minimum times for green and red signal indications is
user-preselectable, and are typically set at 1.5 seconds red and 1.5
seconds green. The actual meter rates are ideally determined based on
right lane mainline volumes, as discussed later in this chapter.

If the controller recognizes a failure of the demand or passage loops,
then it switches the signal operation into cycled timing.

## 4.2 Ramp Meters as an Element of the Freeway Management System {#ramp-meters-as-an-element-of-the-freeway-management-system .unnumbered}

The following section describes how ramp meters interrelate with the
freeway management system.

1.  Ramp meters in freeway management system-equipped areas are an
    element of the ADOT freeway management system.

2.  In areas where the freeway management system is not yet deployed,
    ramp meters may be used as a stand-alone congestion mitigation
    strategy.

3.  The ramp metering subsystem of the ADOT FMS supports some commands
    to alter the ramp meter rate from the TOC.

## 4.3 Communications with ADOT Traffic Operations Center {#communications-with-adot-traffic-operations-center .unnumbered}

##  {#section-17 .unnumbered}

This section provides a brief overview of how ramp meters communicate
with the ADOT TOC.

1.  Controllers are polled for ramp meter information every 60 seconds
    by the ADOT FMS. The meters return status information in response to
    each poll. Detector information is separately polled in 20-second
    poling cycles.

2.  Ramp meter timing parameters may be downloaded to each 179
    controller from the TOC.

3.  Most ramp meter timing parameters can be uploaded from each 179
    controller to check what timing parameters are currently in the 179
    controller's local database.

4.  Ramp meters are connected to the node buildings over twisted-pair or
    fiber-optic cables. In the node building, the ramp meter data is
    combined with other data and then sent to the TOC over single-mode
    fiber-optic cable.

5.  Multiple 179 controllers are multi-dropped on to the same low-speed
    1,200; 2,400; or 9,600 bps data circuit.

6.  Up to 8 controllers may share a 1,200 or 2,400 bps copper pair data
    circuit.

7.  Up to 30 controllers may share a 9,600 bps fiber-optic data circuit.

8.  Low-speed data from ramp meters is concentrated in node buildings at
    various field locations, using Sun node processors.

9.  SUN node processors communicate with the TOC using a Fiberlign DS-0,
    10-Base-T Ethernet, and SONET OC-12. These processors are used
    regardless of whether twisted-pair or fiber-optic cable is used to
    communicate between the devices and the node buildings.

### 4.3.1 Ramp Meter Message Formats {#ramp-meter-message-formats .unnumbered}

Four message formats are used to control and monitor the ramp meter and
set and modify its operating parameters.  These formats are used to
communicate from the FMS to the ramp meter field controllers. These
formats are:

1.  Format 1 Command

2.  Format 1 Feedback

3.  Format 2 Command

4.  Format 2 Feedback

These four message formats work as follows:

1.  Format 1 Command is used to poll the ramp meter during normal
    operations at regular intervals.

2.  When the ramp controller receives the Format 1 Command, it responds
    with Format 1 Feedback, which includes:

    a.  Number of violations by lane

    b.  Meter status

3.  Format 2 Command is used to read the ramp meter\'s operating
    parameters.

4.  Format 2 Feedback is used by the Controller to send the ramp
    meter\'s operating parameters.

5.  Format 2 Command and Format 2 Feedback are sent on an \"as-needed\"
    basis whenever the ramp meter configuration parameters are to be
    read or modified.   At such times, the Format 2 commands are sent in
    addition to, not in place of, the Format 1 commands.

## 4.4 Integration with ADOT Traffic Operations Center {#integration-with-adot-traffic-operations-center .unnumbered}

The FMS database in the TOC should be updated each time a new ramp is to
be connected to the freeway management system.

1.  To define a ramp meter in the TOC databases the following
    information must be known:

    a.  Physical location (route, direction & cross street)

    b.  Coordinates (latitude & longitude) of cabinet

    c.  Node Processor Number Assigned

    d.  Communications Circuit \# Assigned Primary & Secondary

    e.  Drop \# programmed into the controller memory

    f.  Data rate for the assigned channel

    g.  Detector mapping to physical locations on the roadway

    h.  Adjacent link lengths to upstream and downstream detector/ramp
        meter stations

2.  Although a secondary communication circuit is used in the FMS
    database, the use of secondary communications circuits 01 and 02 has
    been discontinued in current deployments of the FMS due to the high
    level of reliability of the fiber-optic communications.

3.  This information must be programmed into the device database for the
    FMS to recognize the new equipment.

4.  In some cases, ramp metering is further integrated into the TOC to
    operate ramp meters not individually but as a group. The purpose of
    operating ramp meters as a group is to reduce traffic flow to
    downstream bottlenecks, which may be permanent (e.g. a lane drop) or
    temporary (an incident).

5.  The exact format and architecture of the FMS database is documented
    in the Freeway Management System Database Table Reference Manual,
    available from the TOC.

## 4.5 Ramp Metering Rate Selection {#ramp-metering-rate-selection .unnumbered}

### 4.5.1 Arrival Discharge Chart  {#arrival-discharge-chart .unnumbered}

Ramp metering rates can be selected at an individual ramp using a simple
Arrival and Discharge Chart. Exhibit 4.1 shows an arrival discharge
calculation worksheet template, and Exhibit 4.2 is a sample of a
completed worksheet. The chart uses arrival and discharge rates in
vehicles per hour for each six minute or 1/10 hour time interval. The
area of each square in the plot represents 10 vehicles.

The instructions for using the chart are as follows:

1.  Plot arrival rates for each six minute time period in bar graph
    style for the duration of the study period. The arrival times should
    be obtained from traffic counts. The study period should be selected
    to coincide with the relevant peak demand.

2.  On the same chart plot the discharge rate in the same fashion.

3.  Beginning with time zero, move to a point where the arrival rate
    exceeds the discharge rate. This is the starting point where delay
    begins. Vehicles arriving before the starting point experience no
    delay because there is no existing queue and the discharge rate is
    greater than the arrival rate.

4.  For each time interval of the chart to the right of the starting
    point where the queue begins, calculate the area under the arrival
    rate curve by reading the number from the right axis and record on
    Line A.

5.  Repeat for Discharge Rate and Enter on Line B.

6.  Calculate Delta for Each Time Interval. This is the cumulative
    difference of the areas under lines A and B.

7.  Delta continues to increase as long as the arrival rate exceeds the
    discharge rate. At the point where the discharge rate exceeds the
    arrival rate, delta begins to decrease representing dissipation of
    the queue and there is no further delay.

8.  Determine the Maximum Delta and the Sum of the Deltas. Use the
    information to compute the following:

    a.  Maximum Queue, vehicles (Maximum delta \* area of each square)

    b.  Maximum Queue Length, feet (Maximum queue \* headway)

    c.  Total Delay, vehicle-hours (Sum of the Deltas)

    d.  Total Vehicles Delayed, vehicles (Discharge rate \* time)

    e.  Average Delay (Total delay/total vehicles)

9.  The number of vehicles in the queue at the end of any six minute
    period is equal to the number of arrivals minus the total number
    discharged up to that period.

10. The maximum queue occurs at the end of the six-minute time period,
    which has the greatest difference between the arrival and discharge
    rates.

    ![](media/image17.png){width="7.555555555555555in"
    height="9.63888888888889in"}

    ![](media/image18.png){width="7.555555555555555in"
    height="9.63888888888889in"}

### 4.5.2 Computer Simulation {#computer-simulation .unnumbered}

The use of a model is recommended to develop corridor specific ramp
meter timing plans when a corridor is to be newly metered. (For example,
parts of Loop 101.)

In practice, these calculations are best performed with a computer
simulation model. FREQ12 is a frequently used model for the optimization
of ramp meter rates. FREQ12 can also be used to simulate various ramp
metering scenarios for comparison in terms of user selected measures of
effectiveness such as vehicle or person hours of delay.

The FREQ is a Windows-based program with an interactive graphical user
interface. To simplify operation, the model includes comprehensive input
checking, carefully selected default values, on-screen graphic
representation of the simulation results, and user-selected output
options including traffic performance contour maps. The two models
contained within the FREQ12 system are: FREQ12PE, an entry control
macroscopic model for analyzing ramp metering; and FREQ12PL, an on
freeway priority macroscopic model for analyzing HOV facilities. The
FREQ system of models has received extensive testing over many years and
has been applied to freeway corridors in numerous urban areas throughout
the United States and abroad.

CORSIM is another computer simulation tool that can be utilized. CORSIM
is a microscopic model well-suited for predicting queue lengths and
other operational measures of effectiveness.

## 4.6 Ramp Metering Modes {#ramp-metering-modes .unnumbered}

ADOT ramp meters can run in the following modes:

  ----------------------------------- -----------------------------------
  **Mode**                            **Description**

  1\. Manual                          The user specifies the current
                                      operation of the meter from the
                                      front panel of the controller

  2\. Central Override Mode           Communication with the FMS central
                                      must be present for this mode to
                                      function. The FMS specifies whether
                                      the meter should run with rate 0 to
                                      7.

  3\. Locally Traffic Responsive      The metering rate is selected by
                                      monitoring the volume and/or speed
                                      of traffic flow in the mainline
                                      lanes adjacent to the ramp meter.
                                      The meter selects a range of
                                      operating rates permitted by the
                                      user.

  4\. Time of Day/Day of Week         The times and days when the meter
                                      will operate are constrained by the
                                      user. The meter can be set to
                                      operate either at one of the rates
                                      permitted by the user or in locally
                                      traffic responsive mode.

  5\. Fixed Time                      The meter operates at a set rate at
                                      the times specified by the user and
                                      the days specified by the user.
  ----------------------------------- -----------------------------------

ADOT operates the majority of ramp meters under Time of Day mode. These
ramp meters operate during set time periods during morning and/or
afternoon peak time periods. Of these ramps, some operate with a fixed
cycle rates, while others are locally traffic responsive.

## 4.7 Ramp Metering Rates {#ramp-metering-rates .unnumbered}

Standard ramp meter practice is that the metering rate is determined by
the expected mainline volume and by a decision on how much volume can be
allowed in on the particular ramp. Metering rates can be determined by
analyzing historical volume data for the location. More responsive
metering rates can be established by use of information from upstream
and/or downstream detectors in the mainline, so that ramp metering rates
are computed in real time to respond to current demand levels and
mainline conditions.

Caltrans research suggests the effective operating rate for a ramp meter
ranges between 240 and 900 vehicles per hour per lane. Nine hundred
vehicles per hour in a single lane equates to four-second ramp meter
cycles. In Arizona, three second ramp meter cycles are used to achieve
1,200 vehicle per hour metering rates.

At the other end of the ramp metering rate spectrum, 240 vehicles per
hour equates to a ramp meter cycle of 15 seconds. These cycles typically
consist of two seconds of green and thirteen seconds of red. Longer
cycles tend to lead to high violation rates, poor public perception and
demonstrate a reduced ability to control traffic.

ADOT ramp control firmware supports eight different ramp metering rates.
Rate 0 specifies that the meter is to be off. Rate 7 specifies that the
meter is to display a constant green indication. A constant green
indication is not normally used in Arizona. Rates 1 through 6 can be
user-specified to provide ramp metering with cycles in the range of 3
seconds to 255 seconds. Cycle lengths longer than 15 seconds are not
recommended.

Queue override ramp metering changes the rate plan selected based on the
presence of vehicles on a Queue Detector. The purpose of this feature is
to meter at a faster rate until the queue dissipates.

1.  Until a central ramp control strategy can be implemented, operation
    of the meters in a locally traffic responsive mode using a fixed
    time of day schedule is recommended.

2.  The parameter recommended for selecting the rate plan should be
    right lane mainline detector volume.

3.  Begin metering at rate plan #1 (least restrictive) when the right
    lane volume reaches 1,800 vph.

4.  Gradually increase to rate plan #6 (most restrictive) as the right
    lane volume builds to 2,200 vph.

5.  If right lane volume is not available, move one lane over to the
    left and use that lane's detector information until detector data
    becomes available.

### 4.7.1 Ramp Meter as a Stand-Alone Strategy {#ramp-meter-as-a-stand-alone-strategy .unnumbered}

####  {#section-18 .unnumbered}

Ramp metering is typically implemented along a stretch of freeway at
multiple adjacent on-ramps. However, in addition to improving flow along
a stretch of freeway, ramp metering can also be introduced at individual
locations in order to improve flow condition at that specific location
alone.

Ramp meters can be effective in breaking up platoons to ease merging in
areas where other FMS features are not yet present.

Stand-alone ramp meters can also mitigate localized bottleneck
locations.

### 4.7.2 Default Metering Rates {#default-metering-rates .unnumbered}

The Department has selected a metering plan to achieve systemwide
uniformity in ramp meter operation. The plans are primarily designed to
provide platoon dispersion and slightly spread the peak. The uniform
plans are not intended to create delay of sufficient length to divert
trips from the freeway to surface streets. The standard hours for ramp
meter operations are:

  ----------------------------------- -----------------------------------
  **Period**                          **Time**

  AM Peak                             6:00 -- 9:00 AM

  PM Peak                             3:00 -- 7:00 PM
  ----------------------------------- -----------------------------------

The parameters used in the plan are as follows:

  ----------------------------------- -----------------------------------
  **Parameter**                       **Standard Setting**

  Minimum Green                       1.5 seconds

  Maximum Green                       1.5 seconds

  Minimum Red                         1.5 seconds

  Maximum Red                         10.0 seconds
  ----------------------------------- -----------------------------------

Six uniform metering rates are used:

  ------------- ---------------- --------------- ------------------------
  **Metering    **Rate           **Rate          **Cycle Length
  Level**       (veh/minute)**   (veh/hour)**    (seconds)**

  1             20               1,200           3

  2             18               1,080           3.33

  3             16               960             3.75

  4             14               840             4.29

  5             12               720             5

  6             10               600             6
  ------------- ---------------- --------------- ------------------------

The appropriate metering rate is selected based on the volume of the
right lane of the mainline, as described in the previous section.

To reduce the probability of rear-end collisions, a soft-start of the
ramp metering sequence is recommended. The soft-start sequence for a two
lane ramp meter is typically as follows:

1.  Activate the Flashing Beacon

2.  Wait 10 seconds

3.  Display a green ball in the primary lane while second lane signal
    remains dark.

4.  Begin normal metering operation

### 4.7.3 Recommended Speeds {#recommended-speeds .unnumbered}

The goal of ramp metering is to operate freeways at their highest level
of efficiency. Ramp meters have been shown to increase throughput on
congested sections of freeway up to 3%. Based on the Highway Capacity
Manual, the highest throughputs on freeways are achieved at speeds
between 50 and 53 mph. As a result, the goal of a ramp metering system
is to keep freeway traffic moving at speeds of 50 to 53 mph.

### 4.7.4 Impact of Incidents {#impact-of-incidents .unnumbered}

For the purposes of ramp metering, incidents can be viewed as the
temporary introduction of a bottleneck located downstream of one or more
ramps. By using detection downstream of the incident location, the
actual capacity of the bottleneck can be measured in vph. The goal of
ramp metering is to reduce the rate of vehicles entering the freeway,
without spilling back into the surface streets.

The first step in doing this is to define the freeway segment in which
ramp meters will need to be adjusted or activated. This is typically all
ramp meters upstream of the incident until an unmetered
freeway-to-freeway connector or ramp is encountered.

Either a model or a simple arrival discharge worksheet can be used to
compute suitable metering rates. The most common result of the
calculation, if the capacity reduction is significant, is that all of
the ramp meters on the segment should be operated at the most
restrictive rate permitted by the agency's metering policy (e.g. 240 vph
or until the queue spills back onto the queue detector or the metering
rate has been reduced to 80% of the original ramp volume).

Depending on the upstream capacity reduction, ramp metering rates
downstream of the incident can often be increased or the meters can be
temporarily deactivated.

## 4.8 Ramp Meter Equity {#ramp-meter-equity .unnumbered}

Research to answer the basic question of which members of the community
benefit from ramp metering has sometimes been termed ramp meter equity
in recent literature. In general, ramp metering benefits drivers making
longer trips at the expense of drivers making shorter trips. This
general observation is consistent with the basic purpose of the freeway
system: Making long trips at relatively high speed.

When HOV facilities are provided, HOVs normally benefit at the expense
of single-occupant vehicles. This is consistent with the goal of maximum
movement of people rather than vehicles.

All motorists seem to benefit from ramp metering by making travel times
more predictable. Individuals and businesses located near metered ramps
may, however, suffer from the metering program due to increased
congestion on surface streets near the ramps. Pollutant emissions at
these points may also be greater than they were before the ramp metering
program was implemented.

A ramp meter equity policy should allow the benefits and drawbacks of
ramp meters to be distributed fairly. This is normally done by limiting
ramp waits to a few minutes and ensuring that adequate storage for
queues is provided.

ADOT currently does not have a specific ramp meter equity policy in
place.

## 4.9 Enforcement of Ramp Meters {#enforcement-of-ramp-meters .unnumbered}

Attributes of effective ramp meter enforcement programs in other
jurisdictions are described below. Frequent coordination between the
Department of Transportation and the Department of Public Safety (DPS)
is essential to effective ramp meter enforcement.

1.  To achieve compliance with ramp meter indications, continuous and
    selective enforcement of the ramp meters is required.

2.  Enforcement of ramp meters with HOV bypass facilities should be a
    priority.

3.  A public awareness campaign, specifying the consequences of
    violating a meter should be part of the enforcement campaign to
    encourage voluntary compliance.

4.  Signs indicating the maximum fine amount for a violation are used in
    California to encourage compliance.

5.  Automated enforcement is used in Arizona for red traffic light
    violations. The technology is suitable for ramp meter enforcement.
    Public acceptance of the technology for ramp meter enforcement may
    be more difficult to achieve because the safety arguments in favor
    of deploying the technology are less compelling in the ramp meter
    enforcement application than in the traffic signal enforcement
    application.

# **5. Ramp Meter Maintenance** {#ramp-meter-maintenance .unnumbered}

## 5.1 Personnel {#personnel .unnumbered}

Currently, ADOT uses agency personnel trained in ramp meter maintenance.
A two-person crew should be able to provide preventative maintenance for
up to 50 ramp meters. Additional staff may be needed for unscheduled
maintenance. The qualifications of these personnel include coursework
and military experience in electronics. Journeyman electrician licensing
is a helpful qualification. Trained electricians have the basic skills
required for ramp meter maintenance. Ramp meter maintenance personnel
should also possess at least a Class B commercial drivers license to
allow operation of bucket trucks and line trucks, if heavy maintenance
such as pole replacement will be performed.

Personnel responsible for ramp meter timing adjustments should be
professional engineers, engineers-in-training or traffic engineering
technicians, who have been trained in basic highway capacity and freeway
operations principles.

Contracted personnel may also be used to perform all maintenance
functions or selected maintenance functions. Although ADOT currently
does not contract its ramp meter maintenance functions to the private
sector, many local agencies do contract with private firms that provide
traffic signal maintenance services. These firms possess the basic
skills to maintain ramp meters, as well. Contracted personnel can be
effectively used to overcome deferred maintenance backlogs or perform
special functions such as detector replacement.

## 5.2 Training {#training .unnumbered}

Personnel performing ramp meter maintenance should be trained in the
following areas:

1.  Work Zone Safety

2.  Electrical Safety

3.  Safe work practices/OSHA regulations

4.  ADOT Policies and Procedures

5.  Basic Electronics

6.  Basic Traffic Engineering Principles

7.  ADOT Ramp Control Firmware Operation

8.  Ramp Control Cabinet Hardware

Most employees involved in ramp meter maintenance bring knowledge of
electronics to the job. This knowledge is often derived from military
training or a community college electronics technology program.

Effective training in traffic engineering principles is needed for
individuals who do not have formal schooling in this area. The
International Municipal Signal Association (IMSA) offers certification
classes in closely related fields including:

1.  Work Zone Safety

2.  Signing & Striping I & II

3.  Traffic Signals I, II and III

A Traffic Engineering Technician course is also available through
Northwestern University, for individuals desiring a more in-depth
understanding of traffic engineering principles.

Training on ADOT's specific control equipment is also provided by FMS
contractors installing each new Phase of the FMS. These sessions provide
introductions to the 179 controller hardware, fiber-optic
communications, and other FMS equipment. The ADOT ramp control firmware
must be learned through on-the-job training.

## 5.3 Commonly Reported Malfunctions {#commonly-reported-malfunctions .unnumbered}

Historically, the three most commonly reported malfunctions in ADOT's
ramp meters are as follows:

1.  Non-functional detectors.

2.  Non-functional load switches.

3.  Two simultaneous green signal indications for adjacent metered
    lanes.

## 5.4 Preventative Maintenance {#preventative-maintenance .unnumbered}

ADOT has established Routine Signal Maintenance and Inspection
performance guidelines that document the preventative maintenance (PM)
that should be performed for each ramp meter site.^12^ This document
lists the following PM tasks that should be performed every three
months:

At controller:

1.  Check timing of all controllers as per timing card.

2.  Clean all fixed components and wiring harnesses.

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1.  Tighten and secure all mounting hardware and terminal connection
    screws.

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4.  Check ventilating fans and thermostats. Install new dust filters.

5.  Lubricate locks, ventilating fan motors and graphite the cabinet
    locks.

6.  Check voltage and current for abnormal readings.

7.  Recaulk controller cabinet if necessary.

8.  Remove graffiti from cabinet.

In the field:

1.  Check alignment and operation of signal heads. Assure proper
    orientation of optically programmed and louvered signal heads.

2.  Assure that all poles have handhole covers.

3.  Check condition of all pull boxes and covers.

4.  Check condition and operation of all detectors.

5.  Replace inoperative lamps.

6.  Make minor repairs to loops.

7.  Check for missing pole number stickers and replace if necessary.

In addition, the following PM activities should be performed:

1.  Check communications system (Verify send and receive of local
    modem.)

2.  Check controller clock.

3.  Verify timing parameters.

4.  Log service activities performed.

For annual maintenance, the following PM activities should be performed:

1.  All incandescent ramp meter bulbs should be replaced during an
    annual maintenance visit.

2.  When Light Emitting Diode (LED) signal indications are used, the
    relamping frequency is typically three to seven years.

3.  Signs and signal heads and beacon lenses should also be washed
    during the annual maintenance visit, if needed.

#########  {#section-19 .unnumbered}

## 5.5 Unscheduled Maintenance {#unscheduled-maintenance .unnumbered}

This task involves responding to malfunctioning ramp meters upon
request. An individual should be on call-back duty at all times to
respond to unscheduled maintenance requests. If the individual is unable
to rectify the problem during an after hours site visit, the ramp meter
may be deactivated and repaired during normal working hours.

## 5.6 Detection Maintenance {#detection-maintenance .unnumbered}

Detection maintenance is often deferred due to the difficulty in
maintaining loop detectors under live traffic. A list of non-functioning
detectors should be kept current at all times, so that detection
maintenance crews can take advantage of other closures in the area to
perform detection repair or replacement. To avoid indefinite deferral of
detection maintenance, detection maintenance should be scheduled for
each freeway segment at least once every one to two years. Because of
the specialized equipment involved many agencies will contract this
service to a specialist firm.

## 5.7 Maintenance Documentation {#maintenance-documentation .unnumbered}

A basic cabinet log should be maintained. The cabinet log should
include:

1.  The date and time of the visit.

2.  The purpose of the visit (e.g. PM, report of red lamp out, etc.).

3.  The action taken.

4.  The name of the responsible employee.

Identical information should be kept in the maintenance worker's truck
for regular management reporting. In addition, the maintenance worker
must keep a record of supplies and materials used.

## 5.8 Maintenance Evaluation {#maintenance-evaluation .unnumbered}

The reports obtained from individual maintenance workers should be
compiled into management reports by a maintenance supervisor. The
management reports can then be used to assess the effectiveness of the
current maintenance program and to determine if any changes in the
current maintenance program are required. Information contained in
management reports should include:

1.  Number & type of services performed

2.  Labor hours expended by classification for regular and overtime

3.  Materials used versus budgeted materials for the month and fiscal
    year to date

4.  Ongoing listing of deferred maintenance needs and aging report for
    deferred maintenance items.

5.  Other data needed to track whether the organization is meeting its
    goals (e.g. mean time between failure & mean time to repair.

# **Acronyms** {#acronyms .unnumbered}

AASHTO: American Association of Highway Transportation Officials

AC: Alternating Current

ADOT: Arizona Department of Transportation

AQD: Advance Queue Detector

ATMS: Advanced Traffic Management Systems

AWG: American Wire Gauge

BPS: Bits Per Second

DC: Direct Current

DHV: Design Hour Volume

DPS: Department of Public Safety

EIA-232: Electronic Industries Alliance Standard for Serial
Communication

FMS: Freeway Management System

FREQ: Family of Computer Simulation Models for Traffic Operations

GFCI: Ground Fault Circuit Interrupter

HCM: Highway Capacity Manual

HOV: High Occupancy Vehicle

IMSA: International Municipal Signal Association

K: Kilo

L~a~: Acceleration Length

L~g~: Gap Acceptance Length

LED: Light Emitting Diode

LOS: Level of Service

MPH: Miles per Hour

MUTCD: Manual on Uniform Traffic Control Devices

NVRAM: Non-Volatile Random Access Memory

OSHA: Occupational Health and Safety Administration

PDA: Power Distribution Assembly

PHV: Peak Hour Volume

PROM: Programmable Read Only Memory

RV: Ramp Volume

RS-232: Electronic Industries Alliance Standard for Serial Communication

SOV: Single-occupant Vehicle

SS-50: Standard for Industrial Data Bus

TOC: Traffic Operations Center

TSM: Transportation System Management

VAC: Volts Alternating Current

VPH: Vehicles per Hour

# **Glossary** {#glossary .unnumbered}

Acceleration Length: A distance along the ramp that allows for safe
acceleration of vehicles to merge with mainline traffic.

Advance Queue Detector: An inductive loop located along the ramp near
the surface street used to monitor whether the queue has reached a
certain length.

Clear Zone: An unobstructed area provided beyond the edge of traveled
way for the recovery of errant vehicles, including shoulders.

Demand Detector: An inductive loop used to monitor if a vehicle is
immediately upstream of the ramp meter stop bar.

Enforcement Area: A paved area adjacent to the traveled way downstream
of a ramp meter stop bar, used law enforcement vehicles.

Flashing Beacon: An advance warning device used to alert motorists to
the presence of the ramp meter.

Gap Acceptance Length: A section of the ramp that provides sufficient
time and distance to allow safe performance of a desired merging
maneuver. Measured as the distance from nose of the ramp to the point of
convergence.

High Occupancy Vehicle (HOV): Vehicles that carry two or more people.

Hourly Volume: The number of vehicles passing a given point along the
roadway during one hour.

HOV Bypass: Lanes or other facilities that allow HOV vehicles to pass by
a ramp meter without having to stop at the signal.

HOV Interrupt Detector: An inductive loop located in an HOV lane used to
provide gaps for HOV vehicles.

Level of Service (LOS): A qualitative rating of the effectiveness of a
highway in serving traffic, measured in terms of operating conditions.
The Highway Capacity Manual identifies operating conditions ranging from
\"A\" for free flow operations to \"F\" for forced or breakdown flow.

Modal Shift: A change in travel demand characterized by use of alternate
modes such as transit, HOV, ridesharing, bicycles, etc.

Model 179 Controller: A microprocessor unit located in a field cabinet
used to control the ramp metering operation.

Nose of Ramp: A point along the ramp having some dimensional width that
separates the ramp from the mainline.

Passage Detector: An inductive loop used to monitor if a vehicle is
immediately downstream of the ramp meter stop bar.

Point of Convergence: The point along a ramp lane where width of the
ramp lane decreases to below the standard lane width and the ramp merges
with mainline.

Queue Storage Length: The length along the ramp that is capable of
holding a queue of vehicles approaching the ramp meter without spilling
over to the surface street.

Ramp Meter: Traffic control signals that control the flow of traffic
entering a freeway facility.

Spatial Shift: A change in travel demand characterized by the use of
alternate routes.

Temporal Shift: A change in travel demand relative to time.

Traveled Way: The portion of the roadway for the movement of vehicles,
exclusive of shoulders, frequently defined by striping.

# **References** {#references .unnumbered}

1.  American Association of State Highway and Transportation Officials,
    [A Policy on Geometric Design of Highways and Streets]{.underline},
    Fourth Edition, Chapter 10, page 827- 869, 2001.

2.  Arizona Department of Transportation, Intermodal Transportation
    Division, [Plan and Profile of Proposed State Highway Phoenix
    District (I-10, I-17, SR-51, US-60) CM-900-0(196)P, 999 MA 000,
    Phoenix Area Ramp Meters]{.underline}, March 31, 1999.

3.  Arizona Department of Transportation, Intermodal Transportation
    Division, [Plan and Profile of Proposed State Highway Phoenix
    District (I-10, I-17) CM-900-A(31), 999 MA 000, Ramp Metering
    Conversion Preliminary 95% Review]{.underline}, 2002.

4.  Caltrans Traffic Operations Program, Department of Transportation,
    Business, Transportation and Housing Agency, [Ramp Meter Design
    Guidelines]{.underline}, January 2000.

5.  Caltrans Traffic Operations Program, Department of Transportation,
    Business, Transportation and Housing Agency, [Ramp Meter Design
    Guidelines]{.underline}, August 1995.

6.  Cambridge Systematics, et al, [Executive Summary, Twin Cities Ramp
    Meter Evaluation]{.underline}, February 1, 2001.

7.  Federal Highway Administration, [Millennium Edition, Manual on
    Uniform Traffic Control Devices]{.underline}, 2001.

8.  Kimley-Horn & Associates, [Background Technical Memorandum Ramp
    Metering FAST]{.underline}, prepared for Nevada Department of
    Transportation, February 22, 1999.

9.  Kimley-Horn & Associates, [Arizona Department of Transportation,
    Freeway Management System Design Guidelines]{.underline}, September
    2002.

10. JHK & Associates, [Utah Department of Transportation, Ramp Meter
    Design Statewide Design Guidelines]{.underline}, February 1997.

11. Transportation Research Board, National Research Council,
    [Highway]{.underline} [Capacity Manual]{.underline}, Chapter 13 and
    25, 2000.

12. Arizona Department of Transportation, Intermodal Transportation
    Division -- Highway Maintenance, [Performance Guideline; Routine
    Signal and Lighting Maintenance and Inspection Form]{.underline},
    2002.

13. Arizona Department of Transportation, Roadway Engineering Group,
    [Memorandum -- Design of Urban Freeway Entrance and Exit
    Ramps]{.underline}, May 18, 2001.