**Commercial Vehicle Information**

**Systems and Networks (CVISN)**

**Electronic Screening Functional Specification**

**and Conceptual Design,**

**I 70 Westbound West Friendship, MD**

Baseline Version

POR-01- 7327 V1.0

July 2001

  ---------------------------------------------------- -----------------------------------
  Prepared for:                                        Prepared by:

  ![](media/image1.wmf){width="1.1979166666666667in"   ![](media/image2.wmf)
  height="1.0444444444444445in"}                       

  US Department of Transportation\                     The Johns Hopkins University\
  Federal Motor Carrier Safety and Administration      Applied Physics Laboratory
  ---------------------------------------------------- -----------------------------------

> > *The Motor Carrier Safety Improvement Act was signed into law on
> > December 9, 1999. This act established a new FMCSA within the US
> > DOT, effective January 1, 2000. Prior to that, the motor carrier and
> > highway safety program was administered under the Federal Highway
> > Administration (FHWA).*
>
> > *The mission of the FMCSA is to improve truck and commercial
> > passenger carrier safety on our nation's highways through
> > information technology, targeted enforcement, research and
> > technology, outreach, and partnerships. The FMCSA manages the
> > ITS/Commercial Vehicle Operations (CVO) Program, a voluntary effort
> > involving public and private partnerships that uses information
> > systems, innovative technologies, and business practice
> > reengineering to improve safety, simplify government administrative
> > systems, and provide savings to states and motor carriers. The FMCSA
> > works closely with the FHWA's ITS JPO to ensure the integration and
> > interoperability of ITS/CVO systems with the national ITS program.*

**This is a** **Baseline Document**

This is a baseline document. This document has completed internal and
external reviews of previously published drafts and preliminary
versions. All comments received to date have been incorporated or
addressed.

**Note:** This document and other CVISN-related documentation are
available for review and downloading by the ITS/CVO community from the
JHU/APL CVISN site on the World Wide Web. The URL for the CVISN site is:
<http://www.jhuapl.edu/cvisn/>

Review and comments to this document are welcome. Please send comments
to:

Mr. Mark A. Oursler Rm. 8-110A

and

> Mr. Steven J. Severson Rm. 24-E176

11100 Johns Hopkins Laboratory

> Laurel MD 20723-6099
>
> Phone: Mark A. Oursler
>
> \(240\) 228-8353 / Washington
>
> \(240\) 228-5928 / Fax
>
> Steven J. Severson
>
> \(240\) 228-8596 / Washington

\(240\) 228-6645 / Fax

E-Mail:Mark.Oursler@jhuapl.edu

Steven.Severson@jhuapl.edu

***Electronic Screening Functional Specification***

***and Conceptual Design,***

***I 70, Westbound West Friendship, MD***

**Table of Contents**

[1 INTRODUCTION 1--1](#introduction)

[1.1 Purpose of This Document 1--1](#purpose-of-this-document)

[1.2 E-Screening Deployment Objectives
1--2](#e-screening-deployment-objectives)

[2 ELECTRONIC SCREENING OVERVIEW 2--1](#electronic-screening-overview)

[2.1 Transponder Validation 2--1](#transponder-validation)

[2.2 Weight and Height Screening 2--1](#weight-and-height-screening)

[2.3 Safety Screening 2--1](#safety-screening)

[2.4 Credential Screening 2--2](#credential-screening)

[2.5 Random Selection Component 2--2](#random-selection-component)

[2.6 Maryland Department of Transportation (MDOT) Philosophy for
E-Screening\
Deployment
2--3](#maryland-department-of-transportation-mdot-philosophy-for-escreening-deployment)

[2.6.1 Path to MDOT's E-Screening Vision
2--3](#path-to-mdots-e-screening-vision)

[2.6.2 Achieving E-Screening Effectiveness in the Interim Period
2--4](#achieving-e-screening-effectiveness-in-the-interim-period)

[3 OVERVIEW OF E-SCREENING SUBSYSTEMS
3--1](#overview-of-e-screening-subsystems)

[3.1 Roadside Operations Computer (ROC)
3--2](#roadside-operations-computer-roc)

[3.2 Mainline Screening Subsystem 3--3](#mainline-screening-subsystem)

[3.2.1 Advance Prescreening Functional Description
3--4](#advance-prescreening-functional-description)

[3.2.1.1 Mainline WIM Functional Description
3--5](#mainline-wim-functional-description)

[3.2.2 Notification Subsystem Functional Description
3--5](#notification-subsystem-functional-description)

[3.2.3 Compliance Subsystem Functional Description
3--5](#compliance-subsystem-functional-description)

[3.3 Ramp Screening Subsystem 3--6](#ramp-screening-subsystem)

[3.3.1 Static Scale AVI Functional Description
3--7](#static-scale-avi-functional-description)

[3.3.2 Static Scale Functional Description
3--7](#static-scale-functional-description)

[4 CONCEPTUAL DESIGN 4--1](#conceptual-design)

[4.1 Assumptions 4--1](#assumptions)

[4.2 E-Screening Subsystem Flow Capacities
4--1](#__RefHeading___Toc526927358)

[4.3 Restrictions 4--2](#restrictions)

[4.4 E-Screening Equipment Placement Considerations
4--2](#e-screening-equipment-placement-considerations)

[4.4.1 WIM Placement 4--3](#wim-placement)

[4.4.2 Advance Prescreening to Notification Subsystem Separation
4--3](#advance-prescreening-to-notification-subsystem-separation)

[4.4.3 Notification Subsystem to Weigh/Inspection Station Ramp Entry
Separation
4--3](#notification-subsystem-to-weighinspection-station-ramp-entry-separation)

[4.4.4 Mainline Compliance Subsystem Placement
4--4](#mainline-compliance-subsystem-placement)

[4.4.5 Electronic Interference from Additional Sources
4--4](#electronic-interference-from-additional-sources)

[5 EXISTING SITE DESCRIPTION 5--1](#existing-site-description)

[6 MARYLAND STATE HIGHWAY ADMINISTRTION/MARYLAND STATE POLICE\
WEST FRIENDSHIP WEIGH/INSPECTION STATION UPGRADED FOR E‑SCREENING
6--1](#maryland-state-highway-administrtionmaryland-state-police-west-friendship-weighinspection-station-upgraded-for-e-screening)

[7 E-SCREENING OPTION 1 -- MAINLINE AND RAMP SCREENING
7--1](#__RefHeading___Toc526927368)

[7.1 Option 1 Site Configuration 7--1](#option-1-site-configuration)

[7.2 Option 1 System Components 7--1](#option-1-system-components)

[7.2.1 AVI 7--1](#avi)

[7.2.2 Mainline and Ramp WIM 7--2](#mainline-and-ramp-wim)

[7.2.3 Automatic Vehicle Classifier (AVC)
7--2](#automatic-vehicle-classifier-avc)

[7.2.4 Vehicle Tracking Loops 7--2](#__RefHeading___Toc526927374)

[7.2.5 Automatic Signals and Signs 7--2](#__RefHeading___Toc526927375)

[7.2.6 Vehicle Monitoring Cameras 7--3](#__RefHeading___Toc526927379)

[7.2.7 Computer Hardware 7--3](#computer-hardware)

[8 E-SCREENING OPTION 2 -- MAINLINE AND RAMP SCREENING
8--1](#e-screening-option-2-mainline-and-ramp-screening)

[8.1 Option 2 Description 8--1](#option-2-description)

[8.2 Option 2 System Components 8--1](#option-2-system-components)

[9 RECOMMENDATIONS 9--1](#recommendations)

[10 REFERENCES 10--1](#references)

***Electronic Screening Functional Specification***

***I 70, Westbound West Friendship, MD***

Table of Figures

[**Figure 3-1 I-70 Westbound West Friendship E-Screening System**
3--1](#__RefHeading___Toc525546324)

[**Figure 3-2 Roadside Operations Computer Functional Overview**
3--3](#__RefHeading___Toc525546325)

[**Figure 3‑3 Mainline Screening Subsystem** 3--4](#Figure33)

[**Figure 5-1 West Friendship Present Site Layout**
5--2](#__RefHeading___Toc525546327)

[**Figure 7-1 E-Screening Option 1 Site Layout West Friendship, MD,
Mainline** 7--4](#__RefHeading___Toc525546328)

[**Figure 7-2 E-Screening Option 1 Site Layout West Friendship, MD,
Ramp** 7--6](#__RefHeading___Toc525546329)

[**Figure 8-1 E-Screening Option 2 Site Layout West Friendship MD,
Mainline** 8--2](#__RefHeading___Toc525546330)

This Page Intentionally Blank

# INTRODUCTION

Screening, as applied to commercial vehicles, is a selection mechanism
to make efficient use of limited fixed Weigh Station and Inspection
resources. Electronic Screening (E-Screening) is the application of
technology to this process, in order to have a computer automatically
make an informed decision about whether further examination of a vehicle
is required. Properly implemented, E-Screening results in improved
station traffic flow, focused vehicle inspections, increased compliance,
and ultimately achieves the goals of increased safety and reduced
operating costs.

In Electronic Screening:

-   Electronic Data Interchange (EDI) is used to transmit safety and
    credentials data to provide input to be used in the screening
    decision.

-   Automatic Vehicle Identification (AVI) is used to identify the
    vehicle while in motion on the mainline approach to the weigh
    station and while on the ramps, store and transfer other screening
    data, and signal the driver with the pull-in decision. \[[Refer to
    reference (a).](#Referencea)\]

-   Weigh In Motion (WIM) scales are used to weigh vehicles in motion
    and overheight detectors are used to detect vehicles that are too
    tall; both are inputs to the screening decision.

E-Screening is consistent with the concepts specified in the national
Commercial Vehicle Information Systems and Networks (CVISN) Architecture
and it is a part of the Maryland CVISN effort. A prototype E-Screening
system has been integrated into the JFK I-95 Southbound weigh station at
Perryville, MD. \[[Refer to references (b) and (c).](#Referencec)\]

## Purpose of This Document

The Maryland State Police (MSP) and State Highway Administration (SHA)
are currently in the planning and procurement stages for the replacement
of the Static Scale and a single lane ramp WIM weight sorter at the I-70
Westbound West Friendship Weigh/Inspection Station site. Specifications
are being developed with consideration of the incorporation of
E-Screening.

This document provides JHU/APL's recommendations for the incorporation
of E-Screening at West Friendship based on the results of JHU/APL's
evaluation of the Weigh/Inspection Station. Recommendations are
presented for placement of E-Screening components.

Not all traffic safety aspects of the proposed options have been
investigated. This includes issues such as safe distances for truck lane
changes and braking in the presence of curves and downgrades. These
issues must be addressed by SHA and MSP before concluding that the
E‑Screening designs contained in this document are practical for this
site.

Top-level site layout and system design for the West Friendship site are
included in this document along with functional descriptions of the
various E-Screening components. The operational scenario and high-level
data flow for E-Screening are described.

Detailed physical specifications and software design for the E-Screening
system are not included in this document.

## E-Screening Deployment Objectives

The following objectives have been established for E-Screening
deployment:

-   Provide the State of Maryland with E-Screening systems that give
    focused vehicle safety enforcement and inspections, increased
    compliance, and improved station traffic flow,

-   Reduce travel delays and associated operating costs for commercial
    vehicle operators participating in the E-Screening program, and

-   Fully conform to the CVISN architecture and objectives for
    E-Screening.

# ELECTRONIC SCREENING OVERVIEW

There are five major components in the process of E-Screening:

1.  Transponder/vehicle identification and validation

2.  Weight & Size Screening

3.  Safety screening of the carrier and vehicle safety history contained
    in the database

4.  Credentials screening, based on specific credential violations or
    history information contained in the database

5.  A random selection factor to randomly pull-in a selected percentage
    of vehicles and a maximum pull-in rate to moderate the flow of
    traffic through the station.

Selection for pull-in will be made even if only one of these components
denies bypass, regardless of the other conditions.

The factory-programmed transponder ID provides carrier and vehicle
identification and allows the E-Screening system to retrieve the
appropriate snapshots from the CVIEW (Commercial Vehicles Information
and Exchange Window) database for screening.

## Transponder Validation

Validation is conducted by checking the factory-programmed transponder
identification number against a screening system database of authorized
transponders. Only transponders enrolled in the Maryland E-Screening
program will be processed; all others will be treated as if they do not
exist. This step is necessary to preserve the propriety of transponders
issued by other agencies to drivers or carriers that have not elected to
enroll in the Maryland E-Screening program.

## Weight and Height Screening

Weight and height screening are based on the weight estimates from the
WIM sensors and on the overheight detectors co-located with the WIMs.
There are several elements involved in this method of weight and height
screening:

-   A weight pass/fail threshold set to some percent of the legal
    weight,

-   An overheight detector set to the maximum legal height plus a small
    buffer, and

-   WIM error conditions are provided from the WIM system to the
    screening algorithm.

## Safety Screening

Safety screening will be based on carrier safety and inspection history
data derived from snapshots received from the MD Commercial Vehicles
Information Exchange Window (CVIEW). The goals of safety screening are
to:

-   Focus inspection resources on those carriers and vehicles that are
    most likely to be in violation, and

-   Provide the benefit of (usually) bypassing the station to those
    carriers that have good safety histories.

A screening process is necessary because there are not sufficient
resources to inspect every vehicle and driver, due to the time-intensive
nature of the inspections. To meet the goals defined above, the
screening algorithm is designed to pull in mostly unsatisfactory or
unidentified vehicles, while stopping only a small portion of the
transponder-equipped AVI vehicles not otherwise flagged by the screening
algorithm.

The safety screening criteria are set from the ROC.

## Credential Screening

Credential screening identifies vehicles that have very specific
inspection or review needs. The following elements are used in
credential screening:

-   Missing or invalid credentials

-   IFTA check status for Carrier

-   IRP or Trip Permit status for Vehicle

-   Manual selection for specific Carrier or Vehicle

The operator at the ROC sets the credential screening criteria.

## Random Selection Component

A random selection element is included in the safety screening method
described above in Section 2.3. The random selection component selects
vehicles randomly to be directed to the Static Scales. Even the
best-rated carriers and vehicles should be occasionally examined to
verify their continued compliance. This also ensures that there will be
a continuous flow of vehicles to the Static Scale to support visual
selection for inspection and inspection data collection.

In addition, it is essential for the station operators to have control
over the overall screening rates in order to moderate the traffic flow
through the station. A "control valve" is implemented, referred to as
the "maximum random sort rate." This value can be applied to adjust the
pull-in rate for all vehicles by an equal amount.

The actual pull-in rate for any individual vehicle is the product of the
screening pull-in rate and the maximum random sort rate. However, if
there is any other clear reason for pull-in, such as a safety violation,
the vehicle will be pulled in.

The operator at the ROC sets maximum random sort rate parameters.

## Maryland Department of Transportation (MDOT) Philosophy for E‑Screening Deployment 

MDOT's philosophy for E-Screening development and deployment is evolving
as information and experience is gained. MDOT would like to implement
systems that conduct Mainline Screening with AVI and WIM and rely on
Static Scales for enforcement. The prototype system at Perryville
southbound also incorporates Ramp Screening as an interim capability;
but MDOT hopes to be able to move away from the need to conduct Ramp
Screening as the number of Maryland enrolled transponders grows. The
issues are as follows.

### Path to MDOT's E-Screening Vision

In the ideal situation, a great percentage of the commercial vehicles
will have enrolled transponders and the Mainline WIMs will have the
accuracy to allow the weight threshold to be set very close to the legal
limits. Both of these conditions must be satisfied to ensure that only
the vehicles most in need of closer inspection are directed into the
Weigh/Inspection Station and to ensure that the flow through the station
is sustainable without backing up the queue.

The effectiveness of any E-Screening program depends on enrolling large
numbers of commercial vehicles and equipping them with transponders that
will enable them to be identified and weighed before they enter the
Weigh/Inspection Station. Only transponder-equipped vehicles can be
identified and signaled to bypass the station. Unless a significant
portion of the commercial vehicles that pass a particular station are
enrolled in the program, there will still be significant queuing backup
problems at the station and the merits of E-Screening may be
overshadowed by an apparent lack of effectiveness.

At the present time, early in the Maryland E-Screening program, the
number of enrolled transponders is small. Additionally, the actual WIM
performance of a deployed system has still not been established; that
will be a product of the studies being conducted by JHU/APL at
Perryville during 2001-02.

This situation creates a quandary for MDOT, the Maryland enforcement
agencies, and for E‑Screening developers as they attempt to implement
additional E-Screening sites.

On one hand, everything possible is being done to accelerate the
enrollment of commercial carriers in the program. Since the transponders
cost about \$40 per vehicle, the incentive to participate must be clear.
Maryland is attempting to create this incentive by offering the benefit
of being able to use a single transponder for E-Screening and for
EZ-Pass toll facilities in the Northeast. A Maryland E-Screening Pilot
Program is being conducted and it is expected that the success of this
program with transponder interoperability will lead to more rapid
enrollment when the program is opened to all carriers later in 2001.

On the other hand, the E-Screening prototype site at Perryville and the
ones to immediately follow (including West Friendship) must function
with high effectiveness from the drivers' perspectives. This will
provide the additional incentive for drivers to participate.

### Achieving E-Screening Effectiveness in the Interim Period

Achieving effectiveness in the interim period before large numbers of
vehicles are enrolled requires some additional flexibility in the system
design to ensure that traffic flow in and around the station is
maintained. Ramp Screening is a key component of this interim
capability. Ramp Screening provides AVI, WIM, and overheight detection
focused on effectively sorting vehicles without transponders that enter
the ramp while also accommodating transponder equipped vehicles. Ramp
Screening substitutes a Notification sign to communicate the screening
decision to the driver instead of using the transponder. Essentially,
Ramp Screening consists of sorting based on the weight of the vehicles
crossing the Ramp WIM. The maximum sort rate is set to balance the flow
through the station so that enough trucks are returned to the mainline,
via a bypass lane, to ensure that the Static Scale queue does not back
up excessively.

As experience is gained at Perryville, the accuracy of the Ramp WIM vs.
the Mainline WIM will be established. This will help to determine
whether a Mainline WIM can function effectively as the only
weight-screening device. This may lead to technical improvements in the
Mainline WIM, the use of alternate WIM sensors, or may establish a
clearer need for the adherence to ASTM standards for the flatness of the
road surface in advance of and trailing the Mainline WIM sensors.

This report is based on the assumption that a Mainline AVI and WIM
system coupled with Static Scale in the Weigh/Inspection Station will be
the final desirable configuration at the West Friendship site in the
future. Due to the limited number of vehicles currently enrolled in the
Maryland E-Screening program, the options presented include a Mainline
and Ramp screening since these present the most workable configuration
at this site in the near term. This site may not require Ramp Screening
in the future as the number of enrolled vehicles continues to grow.
Future sites may also not require Ramp Screening to be workable.

# OVERVIEW OF E-SCREENING SUBSYSTEMS

Figure 3-1 illustrates the following three E-Screening subsystems that
could be implemented at I‑70 Westbound West Friendship:

-   Roadside Operations Computer (ROC) and software

```{=html}
<!-- -->
```
-   Mainline Screening subsystem

```{=html}
<!-- -->
```
-   Ramp Screening subsystem

[]{#__RefHeading___Toc525546324 .anchor}![](media/image1.wmf)**Figure
3-1 I-70 Westbound West Friendship E-Screening System**

Shown are the data interchanges between these components and the
external interface to the MD CVIEW system.

The functional separation of the Ramp and Mainline screening subsystems
permits flexibility in the adaptation of this design. Physically, the
associated software modules can reside on the same or on separate
computers.

## Roadside Operations Computer (ROC)

The ROC is the primary operator interface to the E-Screening system
(maintenance and trouble shooting functions may require access to the
screening or subsystem computers). The ROC allows the operator to
perform the following functions:

-   Set carrier and vehicle screening criteria for safety and
    credentials information contained in the snapshots

-   Receive carrier and vehicle snapshots, individually or by
    subscription from the MD CVIEW

-   Display carrier or vehicle snapshot data

-   Display screening event data, such as WIM weight and classification
    data, carrier and vehicle identification if identified by AVI, and
    pull-in or bypass status and reasons.

[Figure 3-2](#Figure44) presents the major functions and interfaces to
the ROC. The software design for the ROC is contained in [reference
(d)](#Referenced).

[]{#__RefHeading___Toc525546325 .anchor}![](media/image1.wmf)**Figure
3-2 Roadside Operations Computer Functional Overview**

## Mainline Screening Subsystem

The Mainline Screening software receives screening data tables from the
ROC. It also receives transponder identification information from the
Advance Prescreening subsystem that includes vehicle identifiers from
the Advance Prescreening AVI and weight and axle data from the Mainline
WIM. The screening algorithm makes the bypass/pull-in decision. The
decision is transmitted to the vehicle via the Notification Subsystem.
The Compliance Subsystem is used to detect and identify vehicles
bypassing the station. Status and event data from the Mainline Screening
Subsystem are passed to the ROC for display.

[Figure 3-3](#Figure45) illustrates the major functions and interfaces
of the Mainline Screening Subsystem.

![](media/image1.wmf)[]{#Figure33 .anchor}

**Figure 3‑3 Mainline Screening Subsystem**

### Advance Prescreening Functional Description

Commercial vehicles must be in the right lane in order to pass through
the Advance Prescreening AVI read zone and over the WIM sensors. Drivers
of vehicles enrolled in the MD E-Screening program will be alerted to
drive in the right lane by fixed signs located on the approach to the
Advance Prescreening site.

The Advance Prescreening AVI's function is to identify all vehicles
enrolled in the Maryland E‑Screening program. If no transponder exists
or the transponder is not enrolled in the MD E‑Screening program, then
the vehicle will be treated as an unidentified vehicle, which must exit
into the Weigh/Inspection Station. If the vehicle does have a MD
enrolled transponder, the Advance AVI delivers a screening message,
including the carrier and vehicle identifiers to the screening computer
where they are used to perform safety and credential checks in order to
make a screening decision about whether to clear the vehicle to bypass
or direct the vehicle to pull into the station.

All vehicles in the right lane will also be weighed and classified by
the Mainline WIM and checked for an overheight condition. The Mainline
WIM provides vehicle weight estimates and overheight flag as input to
the mainline screening algorithm. Gross vehicle weight along with axle
weights and spacing are available. Although not as accurate as the
Static Scale, the weight estimates are sufficient to identify a
significant portion of the vehicle traffic that is traveling below
registered weight. The WIM data are used as a component of the screening
decision.

#### Mainline WIM Functional Description

The Mainline WIM measures weights and axle spacing of vehicles that pass
across its sensors. A single right lane is instrumented and
participating drivers are trained to drive in that lane only. The WIM
computer also receives input from an overheight detector. The output
data from the WIM computer includes the following information that is
passed to the screening computer for use in the screening decision:

-   Time of event

-   Gross vehicle weight

-   Axle count and spacing

-   Axle weights

-   Vehicle classification

-   Overheight flag

-   Error Conditions

### Notification Subsystem Functional Description

The Notification subsystem is located far enough downstream of the
Advance Prescreening subsystem so that the Mainline Screening computer
has time to complete all necessary processing as the vehicle approaches.
Since a transponder-equipped vehicle could be signaled to pull in or
bypass, the Notification AVI is located far enough upstream of the
station ramp entry so that the vehicle's driver will be able to react
without endangering other vehicles on the roadway.

Vehicles equipped with a MD enrolled transponder will be notified by In
Cab Notification (ICN) consisting of visual and audio signals informing
the driver to either exit onto the station ramp or to proceed on the
mainline, depending on the results of the screening process. This is
accomplished by a command sent to the transponder from the Notification
AVI that sets the audio and visual indicators. For a bypass decision,
the transponder will be commanded to turn the green lamp on and issue an
audible tone. If the vehicle is to pull in, the red lamp will be
commanded on with an audible tone.

### Compliance Subsystem Functional Description

It is necessary to verify that vehicles are not illegally bypassing the
Weigh/Inspection Station. When the station is open, only commercial
vehicles that have been directed to bypass the station by the ICN signal
should pass through the Mainline Compliance system. If a violation is
detected, an indication is given to enforcement personnel. Vehicles may
accidentally bypass the Advance Prescreening and/or Notification systems
by not being in the right lane. These vehicles are treated by the
E-Screening system as if they do not have transponders; they must enter
the Weigh/Inspection Station.

Compliance AVI and a Mainline Automatic Vehicle Classifier (AVC) system
are located on the mainline, past the point where vehicles have
committed to either enter the station or bypass it. The purpose of the
AVC equipment is to classify vehicles that pass across its sensors. All
mainline lanes are instrumented and this system is co-located with the
Compliance AVI. The output data from the AVC shall include the following
information:

-   Time of event

-   Axle count and spacing

-   Vehicle classification

The AVI checks transponder equipped vehicles to verify that the vehicle
was cleared to bypass the station. Not all mainline lanes must be
instrumented with AVI antennas if participating drivers are trained to
drive in the lanes that are instrumented. Factory-set transponder IDs
will be received from all transponders enrolled in the Maryland
E-Screening program and passed to the screening computer.

## Ramp Screening Subsystem

Ramp Screening can include an entire screening capability with AVI, WIM,
and overheight detection. Ramp Screening will be necessary at West
Friendship as an interim weight sorting capability to provide an
effective E-Screening system during the interim period as discussed in
Section 2.6.2.

All vehicles not cleared on the mainline are required to pull onto a
single lane exit ramp. Vehicles entering the Weigh/Inspection Station
ramp fall into one of the following categories:

1.  Transponder equipped and enrolled in MD, valid legal weight: The
    vehicle has been identified, a valid weight has been recorded, and
    the screening algorithm has determined to bring the vehicle into the
    station for closer review. This may be based on specifically
    identified problems, or may be due to random selection. Closer
    review may be limited to a visual check while on the Static Scale,
    or may include an inspection based on the visual review, on data
    reported back in the screening process, or on random selection.

2.  Transponder equipped and enrolled in MD, invalid or over weight: The
    vehicle has been identified; however, either the WIM failed to
    properly register the weight or the detected weight exceeded the
    threshold.

3.  Transponder equipped, unrecognized: The vehicle is equipped with a
    transponder; however, it may either be unrecognized due to a
    technical problem or not enrolled in MD. The vehicle is treated as
    if it has no transponder and the driver will not see any lights on
    the transponder by ICN.

4.  Transponder equipped, bypassed Advance Prescreening/Notification:
    The vehicle was not in the right lane when it passed the Advance
    and/or Notification site and is treated as if it has no transponder
    and will not be signaled by ICN.

5.  No Transponder; the vehicle must enter the Weigh/Inspection Station.

Upon entering the station ramp, all vehicles are expected to follow the
lane signals. ICN is not used within the station to avoid conflicting
signals between the ICN and the lane signals.

### Static Scale AVI Functional Description

The Static Scale AVI queries transponders of vehicles on the Static
Scales, in order to determine transponder identifiers of enrolled
vehicles. The identifiers will be used to provide the inspection
personnel with the ability to easily call up the screening information
about the vehicle on the scale so that they know why the system selected
this vehicle. It will also allow weight data correlation between the
Static Scale, and Mainline and Ramp WIMs, a key capability for
maximizing WIM accuracy.

### Static Scale Functional Description

The purpose of the Static Scale is to accurately measure the weight of
commercial vehicles for enforcement. The output data from the scale
includes both Gross vehicle weights along with three axle group, or
platform, weights. These weights are passed to the screening computer
for the purpose of comparison to weights measured for the same vehicle
on the Mainline and Ramp WIMs. These data support maintenance of
calibration of the Mainline and Ramp WIMs at the greatest accuracy
possible.

The Static Scale AVI is used to identify MD enrolled transponder
equipped vehicles that are on either of the Static Scales. Safety and
credential data for the vehicle are available to the Static Scale
operator to support visual inspection of the vehicle.

For all transponder equipped vehicles, the available measured weights
for the vehicle from the Mainline WIM, the Ramp WIM and the Static Scale
are saved for later evaluation. These data allow weight data correlation
between the Static Scale, and Mainline and Ramp WIMs.

This Page Intentionally Blank

# CONCEPTUAL DESIGN

## Assumptions

Analysis of the I-70 Westbound West Friendship site was performed based
on these assumptions:

The layout of the Weigh/Inspection Station will remain essentially as
built and as shown on the drawings provided by SHA and the acquisition
of additional land will be very unlikely. The recommendations made in
this report are based on limiting the changes to the general
configuration defined by the plans so that additional land acquisition
is unnecessary.

-   SHA Traffic data shows a maximum of 8 trucks per minute. These are
    hourly averages so true peaks can be even higher. This report is
    based on an input flow of 8 trucks per minute. In order to function
    properly the maximum flow through the static scales plus the bypass
    flow at the ramp WIM plus the bypass flow at the mainline WIM must
    exceed 8 trucks per minute.

-   The layout proposed in this document makes the assumption that a
    Ramp WIM weight sorter will be installed in order to maintain
    traffic flow through the station and prevent queuing backups at the
    static scale.

-   Maryland desires to move toward employing only a single Mainline
    Screening subsystem. A Ramp weight sorter will be required to
    maintain traffic flow as long as a mainline bypass rate is limited
    to less than 63%. This is an issue that must be reassessed by
    JHU/APL, MSP, SHA, and MDOT to determine what the traffic flow will
    be with E‑Screening present.

## E-Screening Subsystem Flow Capacities

-   For a single-lane static scale such as planned for this site, the
    flow capacity is limited to 3 trucks per minute that can cross the
    static scale without causing a queue to form. When a queue starts to
    form, it is assumed that 80 feet per truck are required. If the flow
    into the static scales were the full 8 trucks per minute, the
    queuing rate would be (8-3) 5 trucks per minute. This equates to a
    queue length growth of (80 x 5) 400 feet per minute in the single
    lane leading to the scale.

-   The flow capacity across the Ramp WIM is based on 30 mph (2640
    ft/min), 80-foot long trucks, and 100 foot spacing between trucks.
    The flow capacity across the Ramp WIM is therefore (2640/180) 14.7
    trucks per minute. Since this exceeds the maximum input of 8 trucks
    per minute, a single 30 mph Ramp WIM is determined to be adequate
    for this site.

-   The flow capacity across the Mainline WIM is based on 60 mph (5280
    ft/min), 80-foot trucks, and 200 foot spacing between trucks. The
    flow capacity across the mainline WIM is therefore (5280/280) 18.9
    trucks per minute. Since this exceeds the maximum input of 8 trucks
    per minute, a single 60 mph mainline WIM is determined to be
    adequate for this site.

-   In order to prevent the static scales queue from forming with an 8
    truck per minute input to the system, the combination of the
    Mainline and Ramp Screening must result in 5 trucks per minute to
    bypass, on average. The mainline bypass rate is essentially
    completely dependent on the number of Maryland registered
    transpondered vehicles in the flow. This number is going to be very
    small initially but will grow later as the Maryland program gains
    momentum. For example, if 2% of the truck traffic is bypassed based
    on mainline screening and 98% of the trucks are directed into the
    weigh station ramp; this equates to a flow of (8 x 0.98) 7.8 trucks
    per minute into the ramp. If the mainline bypass rate grew to 10%,
    the flow into the station of would be reduced 7.2 trucks per minute.
    In both of these examples, the flow rates into the ramp still exceed
    the static scale flow capacity of 3 trucks per minute so this
    station will be required to have an effective ramp weight sorting
    capability to further reduce the flow to the static scales. A
    mainline bypass rate of 63% would be required to eliminate the need
    for a Ramp WIM system.

-   The Ramp WIM is designed as a safety valve that is used to balance
    the flow into the ramp with the flow that bypasses the static scales
    and the flow that goes to the static scales without having to
    continuously cycle the station open and closed manually, a situation
    that causes confusion for the drivers approaching the station and
    one which increases the chance that trucks in need of inspection
    will erroneously be allowed to bypass. The operators accomplish this
    balance with the adjustment of the "maximum pull-in rate" parameter
    for the WIM. For example, when the flow into the ramp is 7.8 trucks
    per minute (from the 2% mainline bypass example above), the
    effective ramp bypass rate must be (7.8-3) 4.8 trucks per minute.
    This equates to a 62% bypass rate at the Ramp WIM and a 38% pull-in
    rate. This can be interpreted to mean that 62% of the trucks that
    enter the ramp must be sufficiently underweight as to not require
    weighing them on the static scale and the maximum pull-in rate must
    be adjusted to cause the trucks to be returned to the mainline.

-   There are no absolute data available for this site that identify
    whether bypass rate of 62% based on weight is justified; however,
    the number of overweight trucks at this an other sites appears to be
    well under this number based on enforcement experience.

## Restrictions

The West Friendship Weigh/Inspection Station layout provides a very
short queuing space of about 300 feet between the start of the bypass
lane and the static scale. This provides space for only 3 to 4 trucks in
the queue before the bypass lane becomes blocked. The spacing from the
start of the bypass lane upstream to the notification sign is about 100
feet and the notification sign is 300 feet downstream of the Ramp WIM.
This is considered the minimum acceptable separation. The ramp
deceleration lane in advance of the Ramp WIM is also of minimal length.

## E-Screening Equipment Placement Considerations

The following general offset and placement criteria were applied to
determine the best placement options for the addition of E-Screening
equipment to the planned Weigh/Inspection Station.

### WIM Placement

Proper placement of the WIM is critical to obtaining accurate readings.
The requirements are directed at minimizing vehicle dynamics that will
contaminate the detection of weight. According to [reference
(e)](#Referencee), the WIM is to be placed on a level (≤ 2% grade for
mainline and ≤1% grade for ramp) and relatively straight (≥1740m radius
for 46m before and after WIM) road surface. The selected location should
also be free of conditions that would result in significant vehicle
acceleration or deceleration. Excessive grade, tight curvature, or
vehicle acceleration/deceleration will result in shifting of the vehicle
weight off of some wheels and onto other wheels, which may result in
erroneous weight detection. The area that the WIM is to be placed must
also be a smooth section of road so that the truck is not bouncing when
crossing the WIM. The road surface must meet ASTM E 1318-94 for flatness
before and after the WIM sensors to achieve specified WIM accuracies. In
sites employing a Mainline WIM, the WIM will be co-located with the
Advance Prescreening AVI and overheight detector.

### Advance Prescreening to Notification Subsystem Separation

A 1000-foot minimum separation between the Advance Prescreening and
Notification subsystems is used. This allows approximately 11 seconds
travel time between the subsystems, an adequate amount of time for the
transponder to be read by the Advance Prescreening AVI and a decision
made by the screening computer to be relayed back to the vehicle's
transponder via the Notification AVI. Separations significantly greater
than 1000 feet increase the amount of cabling necessary to be installed;
but, can be accommodated. Also, if exit or entrance ramps occur between
the Advance and Notification Subsystems, mainline screening cannot be
conducted on vehicles that use those ramps.

### Notification Subsystem to Weigh/Inspection Station Ramp Entry Separation

After the vehicle has been notified to bypass or pull-in from the
mainline onto the ramp leading to the Weigh/Inspection Station, adequate
space is necessary for the vehicle to safely change lanes and decelerate
to 30 mph. The safe distance required for the lane change is dependent
on terrain (e.g., grades) and the road network. A 1300-foot minimum
separation between the mainline Notification Subsystem and Ramp Entry is
used. However, if terrain and road network indicate that additional
space is needed to safely change lanes, a distance of 2600 feet is used.
There cannot be any exit ramp between the Notification Subsystem and the
Weigh Station Ramp Entry because the E-Screening system will be unable
to track vehicles that are directed to bypass that then leave the
highway. If they reenter the highway and bypass the station, they will
mistakenly be flagged as a violator. An entrance ramp can be
accommodated between the Notification AVI and the Weigh/Inspection
Station Ramp Entry but all vehicles entering the highway at this
location must enter the station; they cannot bypass.

###  Mainline Compliance Subsystem Placement

The Mainline Compliance Subsystem must be located downstream of the Ramp
Entry where vehicles are committed to enter the Weigh/Inspection
Station. It must also be located upstream of where vehicles can re-enter
the mainline from the weigh station from the bypass lane or Static
Scales. Consideration should also be given to the placement relative to
the Scale House so that adequate time exists from the point where a
violator is detected and the operators are notified until when the
vehicle passes the Scale House and could be visually identified.
Placement of the Mainline Compliance subsystem upstream of the Scale
House with minimum 1000-foot separation is desirable.

### Electronic Interference from Additional Sources

Field Testing should be done in the area surrounding any planned AVI
systems to identify any possible sources of electronic interference that
could impact the performance of the AVI.

# EXISTING SITE DESCRIPTION

The current as-built configuration of the I-70 Westbound West Friendship
site is as follows:

-   Three westbound mainline lanes of traffic on I-70,

-   Entry ramp from mainline to the Weigh Station,

-   Static Scale with imminent installation of Mettler-Toledo Static
    Scale,

-   Adjacent Static Scale bypass lane

-   Adjacent Scale House,

-   Inspection area located behind Scale House, and

-   Left-hand return to I 70 from Weigh Station.

Figure 5-1 shows the existing site, as built. Note that this drawing has
previously been marked-up with site upgrades that are not part of the
E-Screening upgrade. The new E-Screening components are clearly marked
on all of the following drawings.

[**[Figure 5-1 West Friendship Present Site
Layout]{.underline}**](../Figure%205-1(11x17).pdf)

# MARYLAND STATE HIGHWAY ADMINISTRTION/MARYLAND STATE POLICE WEST FRIENDSHIP WEIGH/INSPECTION STATION UPGRADED FOR E-SCREENING

The current Weigh Station on Westbound I-70 West Friendship is
compatible with E-Screening with some modifications and compromises. Use
of E-Screening at this site would alleviate congestion and safety
concerns due to commercial vehicles queuing onto the highway, subject to
the assumption about the percentage of vehicles enrolled in the Maryland
E-Screening program discussed in section 4.

Based on discussions with MSP and MDOT, both Mainline and Ramp screening
will be implemented in this E-Screening system. Due to the minimal
queuing space at the single Static Scale, it will be essential to
implement efficient Ramp screening until such time that at least 63% of
the commercial vehicles (all enrolled in the Maryland E-Screening
program) are being bypassed by the Mainline Screening system.

Without major changes to the Weigh Station, only one option exists for
placement of the Ramp WIM. This leaves a very short deceleration lane at
the entry to the station. SHA should evaluate the severity of this
configuration and consider increasing the length of this lane.

Two options exist for placement of the Mainline Screening subsystem.
Option 1 will be less expensive to implement due to the reduced
infrastructure required. Option 2 is an alternative in case the
placement of mainline components recommended in Option 1 cannot be
achieved.

These proposed options are presented in the following sections.

This Page Intentionally Blank

[]{#__RefHeading___Toc526927368 .anchor}E-SCREENING OPTION 1 -- MAINLINE
AND RAMP SCREENING

## Option 1 Site Configuration

For this option, the Westbound E-Screening system will include an
Advance Prescreening Subsystem, a Notification Subsystem, a Mainline
Compliance Subsystem, a Static Scale Subsystem, and a Scale House
subsystem as shown in Figures 7-1 and 7-2. The key features of this
layout are:

-   Advance Prescreening subsystem in the right westbound mainline lane
    at the crest of the hill approximately one mile east of the
    Weigh/Inspection Station. This location is downstream of the entry
    ramp from Rt. 32, which ensures that all vehicles passing through
    the Advance system will remain in the system and that vehicles
    entering from Rt. 32 can also be E-Screened. This subsystem includes
    AVI, WIM, and overheight detection.

-   Notification subsystem in the right westbound mainline lane at the
    existing overhead sign approximately 2400 feet upstream of the
    Weigh/Inspection Station Ramp entry. This location is about 1600
    feet downstream of the Advance subsystem. This subsystem includes
    AVI and does In Cab Notification (ICN).

-   Ramp Screening approximately 800 feet upstream of the Scale House at
    the location shown on the SHA drawing. This includes a ramp WIM,
    AVI, overheight detection, and tracking loop.

-   Mainline Compliance Subsystem in all three westbound mainline lanes
    adjacent to the Ramp Entry. This subsystem includes Automated
    Vehicle Classification (AVC) and AVI in each lane.

-   Static Scale subsystem. This includes AVI over each of two lanes, an
    overheight detector, and a Static Scale in the right lane connected
    to supply weight data to the E‑Screening system.

-   Scale House subsystem includes the Roadside Operations Computer,
    screening computer, and interfaces to the station operator console
    and signs.

## Option 1 System Components

### AVI

Four Model 200 DSRC readers will be installed. At the Advance
Prescreening site the reader will be installed with a Hirschman 5910
antenna centered over the right lane. At the Notification site, the
reader will be installed with a Hirschman 5910 antenna centered over the
right lane. At the Compliance/Ramp Entry site the reader will be
installed with four Hirschman 5910 antennas, one each centered over the
right lane, center lane, and left lane with a fourth antenna centered
over the ramp lane at the WIM location. At the Static Scales, the reader
will be installed with two Hirschman 5910 antennas, one each centered
over the right and left lane.

### Mainline and Ramp WIM

[Reference (e)](#Referencee) classifies WIM systems as Type I, II, III
or IV according to application and required performance. The Mainline
and Ramp WIMs to be installed at the Westbound I-70 West Friendship site
should meet the following requirements:

-   Type II WIM performance or better

-   ASTM 1318-94 road surface

-   Installation and maintenance achievable during an overnight lane
    closure

-   100 Mb/sec TCP/IP Ethernet or serial data output.

Subject to accuracy studies being conducted at the Perryville prototype
E-Screening site, revision of the requirements may be placed on this
mainline WIM, particularly the preparation of the road surface according
to ASTM standards.

### Automatic Vehicle Classifier (AVC)

An AVC system is to be used to detect and classify commercial vehicles
bypassing the Weigh/Inspection Station. AVC systems use tracking loops
and axle detectors to determine axle counts, spacing and vehicle speed
information. The Westbound I-70 West Friendship site should use a
three-lane AVC.

### Vehicle Tracking Loops

Inductance loops are used at several points to detect vehicles. These
are required for tracking vehicles, synchronizing signals with the
correct vehicles, and to verify compliance with these signals. Permanent
loops are cut into the pavement using loop cable meeting the IMSA 51-5
Specification (14 AWG). Lead-in cable meeting the IMSA 50-2
specification (one pair, 14 AWG) should also be used.

### Automatic Signals and Signs

Lane signals and controllable message signs are automatically controlled
by the screening computer and coordinated with the detected location of
the vehicle. Precise timing and control of these signals is required in
order to ensure that unambiguous direction is given to the intended
vehicle across a broad range of vehicle speeds. Confusion and safety
issues may result if a driver misreads signals intended for another
driver.

Signs should be under the control of a Programmable Logic Controller
(PLC), which should also serve as the interface to the operator's panel
at the Scale House. The station's PLC should be equipped with an
Ethernet interface for interfacing to the E-Screening system.

###  

### 

### 

### 

### 

### Vehicle Monitoring Cameras

A monitoring camera positioned to view the Advance Prescreening site and
its approach should be installed to monitor traffic.

### Computer Hardware

The ROC and screening computers should meet or exceed the following
specifications:

Processor: GX400: Pentium® 4 Processor, 1.8GHz, 256K Cache, Int NIC &
Int Sound

Memory: 1GB PC800 ECC RDRAM

Monitor: 19 inch Dell P991 in Gray, Flat Display Trinitron®, (18.0
viewable)

Graphics Card: Matrox G450 Graphics Card, 32MB (dual monitor capable)

Hard Drives: (2) 40GB EIDE Hard Drive (7200 RPM)

Floppy Drive: 1.44MB Floppy Drive

Modem: Dell V.90 PCI DataFax Modem for Windows

Zip Drive: Zip 250MB with 1 pack media

CD Drive: 8X CD-RW/DVD-ROM Combo Drive (8X/4X/32X CD-RW & 8X DVD-ROM)

Sound Card: Sound Blaster Live! Value (512 Voice) Sound Card

Speakers: harmon kardon 19.5 Speakers

Operating System: Windows® 2000 Professional with CD using NTFS

Virus Protection: Norton Anti Virus 2001

[]{#__RefHeading___Toc525546328 .anchor}

[**[Figure 7-1 E-Screening Option 1 Site Layout West Friendship, MD,
Mainline]{.underline}**](../Figure%207-1.pdf)

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[[]{#__RefHeading___Toc525546329 .anchor}**[Figure 7-2 E-Screening
Option 1 Site Layout West Friendship, MD,
Ramp]{.underline}**](../Figure%207-2(11x17).pdf)

# E-SCREENING OPTION 2 -- MAINLINE AND RAMP SCREENING

## Option 2 Description

This option is similar to Option 1 with the relocation of the Advance
Prescreening subsystem to the crest of the hill approximately ½ mile
east of Rt. 32 and the Notification subsystem to just downstream of the
entry ramp from Rt. 32 to I-70 Westbound as shown in Figure 8-1.

This option will require longer cable runs to reach the Advance and
Notification subsystems and will not allow vehicles that either exit
from Westbound I-70 to Rt. 32 or enter from Rt.32 to Westbound I-70 to
be screened on the mainline.

## Option 2 System Components

The Option 2 components are the same as for Option 1.

[[]{#__RefHeading___Toc525546330 .anchor}**[Figure 8-1 E-Screening
Option 2 Site Layout West Friendship, MD,
Mainline]{.underline}**](../Figure%208-1.pdf)

# RECOMMENDATIONS

The plans for I-70 Westbound West Friendship Weigh/Inspection Station
have been reviewed and the site has been visited. Two options have been
presented for incorporation of E-Screening into this station; both
include a Mainline Screening system for screening that portion of the
commercial traffic that carry a transponder and are enrolled in the
Maryland E-Screening program and a Ramp Screening system to ensure that
the flow of traffic through the station and to the Static Scale will be
balanced. This is deemed to be the most capable and flexible system and
it is well suited to the present state of E-Screening in Maryland where
the number of enrolled trucks is small. The options involve only the
placement of the mainline components including the Advance/Prescreening
and Notification subsystems. The Ramp layout is the same for both
options.

Trucks enrolled in the MD E-Screening program will realize the greatest
benefit while trucks that weigh below the Ramp WIM selection threshold
will also see a benefit. Over the course of time as the number of
enrolled vehicles increases, the Ramp WIM sorting criteria will be
adjusted to provide bypass to fewer and fewer vehicles based on weight
alone. Ultimately the system will be able to migrate to being a Mainline
Screening system with the Ramp Screening system serving only as a
backup. To achieve this, the Mainline Screening System must bypass at
least 63% of the vehicles it sees.

The most notable problems with the site layout are the extremely short
queuing length from the single static scale to the start of the bypass
lane and the short deceleration lane on the entry to the weigh station.
SHA should evaluate these to determine if the ramp can be lengthened.
This would affect the placement of the Ramp WIM so this evaluation
should be made immediately.

The two options are summarized in the following table.

Design Criteria applied to I-70 Westbound West Friendship

  ----------------------------- ---------------------- ------------------
  Design Criteria (section 4)   E-Screening Option 1   E-Screening Option
                                -- Mainline and Ramp   2 -- Mainline and
                                Screening              Ramp
                                                       ScreeningError:
                                                       Reference source
                                                       not found

  WIM placement on level (≤ 2%  Mainline WIM placement Mainline WIM
  grade for mainline and ≤1%    in mainline right lane placement in
  grade for ramp), relatively   approximately one mile mainline right
  straight (≥1740m for 46m      east of                lane approximately
  before and after WIM), ASTM   Weigh/Inspection       two miles east of
  1318-94 road surface.         Station. Location has  Weigh/Inspection
  Co-locate WIM with Advance    slight curve.          Station. Location
  Prescreening reader/antenna                          is straight
  and overheight detector.                             

  1000 feet minimum separation  Approximately 1600     Approximately 5300
  between mainline Advance      feet separation        feet separation
  Prescreening and Notification between mainline       between mainline
  subsystems.                   Advance Prescreening   Advance
                                and Notification       Prescreening and
                                subsystems             Notification
                                                       subsystems.

  1300 feet minimum separation  Approximately 2400     Approximately 4000
  between mainline Notification feet separation        feet separation
  subsystem and Weigh Station   between mainline       between mainline
  Ramp Entry.                   Notification AVI and   Notification AVI
                                Ramp Entry.            and Ramp Entry

  Mainline Compliance subsystem Approximately 1000     Approximately 1000
  adjacent to ramp and minimum  feet upstream of scale feet upstream of
  1000 feet upstream of scale   house                  scale house
  house                                                

  700 feet between AVI and ETC  Not Applicable         Not Applicable.
  at toll plaza.                                       

  Area free of any electronic   Site testing should be Site testing
  interference that could       performed.             should be
  impact AVI performance.                              performed.
  ----------------------------- ---------------------- ------------------

# REFERENCES

a)  []{#Referencea .anchor}*Standard for Dedicated Short Range, Two-Way
    Vehicle to Roadside Communications Equipment*, ASTM E17.51 Draft
    Version 6, 1995, available on the JHU/APL CVISN Web site
    [http://www.jhuapl.edu/cvisn/](http://www.jhuapl.edu/cvisn).

b)  []{#Referencec .anchor}*Electronic Screening Physical Specification,
    Southbound I-95 at Perryville, MD,* POR-01.7299 V1.0, January 2001

c)  *Electronic Screening Functional Specification and Conceptual
    Design*, POR-01-7298, available on the JHU/APL CVISN Web site
    [http://www.jhuapl.edu/cvisn/](http://www.jhuapl.edu/cvisn).

d)  []{#Referenced .anchor}*Design of the Roadside Operations Computer*,
    SSD-PL-00-0392/POR-00-7211, available on the JHU/APL CVISN Web site
    [http://www.jhuapl.edu/cvisn/](http://www.jhuapl.edu/cvisn).

e)  []{#Referencee .anchor}*State's Successful Practices Weigh-In-Motion
    Handbook, Center for Transportation Research and Education*
    (<http://www.ctre.iastate.edu/research/wim_pdf/index.htm)>, 15
    December 1997.

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