LaRa-OHVD: An Innovative Over-Height Vehicle Detection System to

Protect our Bridges to Prosperity

Abhishek Singhal, Ph.D. Candidate in Transportation Engineering

The City College of New York

A student essay submitted for ITS- NY 2015 Best Student Essay Competition at

2015 Intelligent Transportation Society of New York 22nd Annual Meeting

Saratoga Springs, NY

LaRa-OHVD: AN INNOVATIVE LASER RANGING OVER-HEIGHT VEHICLE DETECTION SYSTEM TO PREVENT BRIDGE STRIKES

Abhishek Singhal, Ph.D. Candidate in Transportation Engineering, singhal@utrc2.org Advisor: Prof. Camille Kamga, Ph.D., ckamga@utrc2.org Co-Advisor: Prof. Anil K. Agrawal, Ph.D., P.E., agrawal@ccny.cuny.edu

Department of Civil Engineering, The City College of New York, CUNY, NY 10031

1. RESEARCH OBJECTIVES 2. BRIDGE HIT PROBLEM

4. STATE OF PRACTICE OHVDs 5. LaRa-OHVDs

7. LaRa-OHVD PROTOTYPE 8. TESTING & RESULTS

3.CURRENT MITIGATION METHODS

9. CONCLUSIONS

ECR SSC

PROBLEM STATEMENT

Over-height vehicle bridge strikes a major problem all over the world. More than 200 bridge hits annually in New York state. Current Over-Height Vehicle Detection Systems (OHVDs) are installed across

the road width up to quarter mile (1320 feet) before the bridge. System & installation costs significantly high (up to $200,000 in some cases). Installation limited to very few locations. No innovation in OHVDS technology in U.S. since 1998

RESEARCH OBJECTIVES

To develop a new over-height vehicle detection system that can be installed on the face of the bridge/overhead gantry/existing roadside infrastructure .

Can detect incoming over-height vehicle at safe stopping distance. Most bridges already have electricity (street lights), telephone connections. Low cost device based on mature LADAR (Laser Detection and Ranging)

technology, special optics and existing traffic engineering guidelines. Mass deployment because of low cost. Better performance features than existing OHVD systems.

Source: Trigg Industries Product Catalog Introduced in 1965, proven effective in reducing hits, used by 15 State DOTS (2011) Consist of pair of aligned optical transmitter-receiver (A), Alarm bell (B) and VMS sign (C) Improvements to basic set up have been limited to:

Modifications in the light source (visible/red/Infrared/laser) Light modulation (visible), Operation Mode: diffuse, reflective or opposed (infrared) Using single, dual beam or Z-beam systems

LIMITATIONS Systems installed at greater distance before the bridge; up to a quarter mile Power & communication lines may have to be brought up to the installation site. Systems require a communication cable between the transmitter and receiver units. Requires digging a

trench across the road width. Results in additional roadway closures & traffic delays. Structural & Installation costs usually much higher than system costs

ITS grade installation $50,000 -$100,000 per approach Stand alone detector-pair cost is also expensive

$9000-$25,000 per approach (Trigg Industries) Installed only at critical locations because of very high costs (entrance ramps). Suffer from false detections due to snow deposits on vehicle, antennas, flying debris or birds. Suffer from alignment issues due to ground heave. Most times, drivers miss the only warning sign. Some do not hear the alarm bell (while listening to

radios, etc.) There is no further line of sight signage to stop them from hitting the bridge. Some OHVDS use expensive VMS/matrix signs ($20,000-$70,000)

LaRa- OHVD : Laser Ranging Over-Height Vehicle Detector

Uniqueness in Operation First OHVDS which can be mounted on the bridge being protected (or overhead gantry/roadside infrastructure). Long range detection (>1000 feet). Detect incoming over height vehicle at safe

stopping distance (570 feet @ 60 mph, Level Grade AASHTO) Broad detection zones instead of single optical beam for sure detection. Eye safe, infrared laser rangefinder based device. Uses a standard freeway sized warning sign with flashing yellow beacons,

installed on the bridge face next to the detector. Meet or exceed current OHVDS performance specifications

Vehicle detection algorithms minimize false detections Minimal System Cost including Detector, Warning Sign, Signals & Installation Line of Sight Warning Sign and Traffic Signal design

Drivers can always see the warning sign No need for expensive VMS/Matrix signs

Provide Over-Height measurement Useful statistic for crash/damage assessment

Collision Prediction by Speed Measurement Pre-emptive Emergency Response & Recovery Controlled Damage due to driver response

By combining a mature vehicle detection technology (LADAR), special optics and existing traffic engineering guidelines; a cost effective Laser Ranging Over-Height Vehicle Detector is developed.

Represents a new sensor innovation in over-height detection in decades. Current OHVDs lack market competition, with archaic operation resulting in very high sensor and

deployment cost. Find limited use at most problematic locations. Thousands of low clearance bridges & overpasses still vulnerable to over-height vehicle hits. LaRa-OHVD is envisioned to detect over-height tractor trailers and large trucks which cause the

maximum number of bridge hits (94 %) in New York State. With respect to New York State, majority (78%) of bridge hits have been found to occur on

Parkways, State Highways and Interstates; where the LaRa detector can be utilized. Actual field testing is required to validate the system utility and note performance limitations. The low cost design, minimal installation, features like broad vehicle detection zones, algorithms

to minimize false detections, line of sight warning sign, collision prediction & over height measurement; makes the LaRa OHVD an innovative concept in over height detection.

LaRa-OHVD has the potential to prevent thousands of bridge strikes; save lives, prevent congestion, save tax payer’s dollars and contribute to the vital infrastructure preservation goals in the United States.

Performance Feature Value

Operating Speed 1-75 mph

Maximum Range (across road width) 200 feet

Minimum size of detected object ¼-4 inch (2 inch)

Alarm/Sign Interface 1-2

False Positives Minimum

Direction Discerning Dual Beam Type

Additional Features

Fail Safe Mode Default Warning Sign Activation

Fault reporting Power Failure, Beam or Sensor Failure, Beam obstruction

Remote Management Interface to TMC, event recorder

Vehicle Detector Road loops to eliminate false positives

New York State: Number of Bridge Hits between 1993-2011

United States: Number of Bridge Hits between 2005-2008

LaRa OHVD: Top View of Installation Proposed Warning Sign with Signals

Detection Concept (Regular Height Vehicle)

Detection Concept (Over-Height Vehicle)

Region 8

Region 5

Region 10 Region 11 New York State: Number of recorded bridge hits by year (* Through 4/20/2015)

~5,000 over-height vehicle bridge hits/year in U.S. result in over $100 million worth of damage to public & personal property

Over-height truck bridge hits resulted in ~20 fatalities (2003-2013) and 75 injuries (2010-2013) per year respectively.

Over-height trucks have resulted in 13,108 structural damage bridge hits in four years (2010-2013).

Societal cost of a major over height vehicle-bridge hit estimated to be $694,000 based on 1994 FHWA figures.

14 European Union Member States, Ireland (>180 hits/year), United Kingdom (>2,000 hits/year), Australia (332 hits between 2005-2013) consider bridge hits as a significant safety risk.

An artist’s rendition of LaRa-OHVDs installation

68% State DOTs consider bridge hits to be a significant problem.

New York State had 1,600 hits since 1993. Many bridges have been repeatedly hit.

Tractor trailers, large trucks constitute majority (98%) of hits.

Bridges over Parkways, State Highways, Interstates most affected

30 States 44 States

Target Passive Effectiveness /Challenges Driver Driver education on bridge hits

Testing on CMV license exams Vehicle height signs in cabin Measuring height of cargo before trip

Developing a new regulation Driver compliance and awareness is required Most challenging to enforce

Structure Protection through in-line barriers (Hanging rods, chains) Sacrificial beams or Bash bars on or before the structure

Costly to implement, Vehicle/cargo damage or driver injury may result in liability issues

Roadway

Efficient posting of over-height warning signs Markings on roadway and structure Provide better lighting conditions

Economical from DOT perspective Limited effectiveness

Target Active Effectiveness /Challenges Driver In-cab proximity alerts (GPS/CB Radio)

Use commercial GPS for trucks/CMVs Utilize DOT oversize permit, escort vehicle services Use authorized truck route maps Real-time truck routing mobile apps

Commercial GPS costly for fleet/truck owners Permit process requires planning Time consuming, enforcement? Low clearance database validity

Structure Alteration of structure height through raising the bridge/overpass or Grinding the roadway surface

100 % effective to eliminate hits Most Cost Prohibitive Solution

Roadway Detection and re-routing using over height vehicle detection (OHVDs) sensors and VMS warning signs

Practical & expensive solution Highly effective in reducing hits

April 13, 2015, $1/month

March 2, 2015, FREE!

An eye-safe (Class 1) infrared laser based prototype developed < USD $4,000 Size of a typical shoe box: L x B x H =12”x 6”x 6” Weight < 3 lbs. Actual product design can further reduce size & weight considerably Custom laser rangefinder design uses special optics to transform the elliptical

laser beam into a thin sheet of laser light (fan shape) Field interface to Traffic Management Center can be integrated All weather performance needs to be tested Mounted on a traditional camera enclosure bracket- simple installation Uses a standard 12” warning traffic signal for higher visibility - Flash rate set as per MUTCD Operational parameters configured through a PC – Serial interface Requires one time on-site calibration Single Lane design, Meets “Performance features” of existing OHVDs “Direction discerning” feature not implemented “Additional features” of existing OHVDs can be implemented

Traffic Signal & Detector Test Set Up

Oblique views of the LaRa detector Front view (left) and Back view (right) of LaRa detector

12 V DC Switches Power

110 V AC /

Traffic Signal

Serial Port

Test Signals

ACKNOWLEDGEMENTS This research is supported by the University Transportation Research Center, Region 2

Optical Testing to validate Laser Beam Shape

8 ft.

Collimated Laser Beam at Detector (left) & at distance of 8 Ft. (Right), 2 cm thickness

LaRa LRF Range Testing & Target characteristics

Beam Resolution @120 Ft (20 mph): 2.36 inch x 2.5 Ft wide @ 220 Ft (30 mph): 3.65 inch x 4.5 Ft wide

Finer focusing of optics can correct beam shape at field distances.

Range limitations due to APD receiver design Height Resolution in Centimeters Vehicle / False Detection Algorithms : Currently Under Development

Triangular laser sheet, 7.2 cm wide @ 8 Ft. (left edge, center, right edge), 2 cm thick

Laser Beam

Propagation

Axis

Design

Divergence

(θ)

Measured

Divergence

(θ)

Beam Size at Field Distance

(645 feet @ 65 mph)

Beam Size at

Test Distance

(220 feet @ 30

mph)

Design

Divergence

Measured

Divergence

Measured

Divergence

mrad mrad Inches Inches Inches

Fast Axis

(Vertical) 0.2 1.085 2.5 9.16 3.65

Slow Axis

(Horizontal) 23.04 20.28 178.8

(14.9 Ft.)

157.86

(13.15 Ft.)

54.33

(4.53 Ft.)

2

Applicant Name Abhishek Singhal

University The City University of New York

Academic Discipline Ph.D. Candidate in Transportation Engineering

Department of Civil Engineering

Anticipated Graduation Date Fall 2015

Mailing Address Abhishek Singhal

Graduate Research Assistant,

University Transportation Research Center Region 2

The City College of New York

160 Convent Avenue, Marshak-910

New York, NY, 10031

Telephone 212-650-8060

Cellphone 347-852-4607

Email singhal@utrc2.org

Faculty Advisor Dr. Camille Kamga

Telephone 212-650-8087

Email ckamga@utrc2.org

LaRa-OHVD: An Innovative Over-Height Vehicle Detection System to

Protect our Bridges to Prosperity

Abhishek Singhal, Ph.D. Candidate in Transportation Engineering,

Department of Civil Engineering, The City College of New York

Abstract

Collisions between over-height vehicles and bridges are a serious problem across the world.

Over Height Vehicle Detection Systems (OHVDs) have been routinely utilized by transportation agencies

to protect their bridges and overpasses. However, high system costs have limited their deployment

making thousands of low clearance structures vulnerable to collisions. A new over-height vehicle

detector based on existing laser ranging technology (LADAR) is developed to overcome the cost barrier

while providing enhanced capabilities as compared to the state of practice OHVDs. Currently under

development, the LaRa OHVD has immense potential to reduce the over-height bridge hits and protect

the integrity of our transportation infrastructure.

Introduction

New York City is an excellent example of how bridges transform a city by providing vital links in

its transportation network. The ~ 600, 000 bridges across the United States (including the 17,000 highway

bridges in New York State) shape the backbone of the American transportation infrastructure enabling

connectivity, commerce and economic competitiveness. However, latest data from the National Bridge

Inventory indicates that close to 145,800 bridges (~ 24%) are structurally deficient or functionally

obsolete [1]. With aging infrastructure and increasing gaps in transportation funding, the bridge agencies

3

now require innovative and cost effective measures to protect and extend the service life of existing and

newly constructed bridges and overpasses.

Over-height vehicle impacts to low clearance bridges, tunnels and overpasses cause significant

damages to transportation infrastructure, create safety risks for the driver of the vehicle and other

motorists on the roadways and often result in closure of the bridges for lengthy periods with costly repairs

[2]. Most importantly, severe or repeated hits may result in reduced design life of bridge structure

resulting in untimely and extremely high replacement cost.

Currently, many State DOTs/bridge agencies utilize Over-Height Vehicle Detector systems

(OHVDs) over roadways to detect the erring vehicles en-route to low clearance structures. This

technology while proven in field for many years; is outdated and has many noted limitations as reported

by State DOTs. Current OHVDs lack market competition, with archaic operation resulting in very high

sensor and deployment cost. Due to this, these systems are only used at most problematic locations

leaving thousands of other bridges & overpasses vulnerable to over-height crashes.

This paper presents a new ITS roadway sensor (currently under development) by our research

group to detect over-height vehicles. The Laser Ranging Over Height Vehicle Detector (LaRa-OHVD)

or simply “LaRa” is a new detection concept in over-height sensing which uses LADAR technology to

infer a vehicle’s height. This mature technology finds many applications in transportation namely, in

LADAR speed guns, vehicle profiling and automotive sensors (e.g. adaptive cruise control). LaRa meets

the operating requirements of current OHVDs while providing marked improvement in detector

capabilities with a very low system cost.

The paper starts with a background review defining the problem scope. State of practice OHVDs

are then presented with their operation and noted limitations. This is followed by a description of the

proposed solution, the sensing methodology and the advantages of the proposed detector. The paper

concludes by summarizing key findings and directions for future research.

Background Literature

The Over-Height Vehicle Bridge Hit Problem

Collisions between over-height vehicles and low-clearance bridges & overpasses (hereby referred

as “over-height bridge hits”) are a major problem in USA and the world. It is estimated that in U.S., there

are ~5,000 low clearance bridge hits per year which cause over 100 million dollars’ worth of damage to

public & personal property [3]. Crash data for large trucks indicates that, over-height bridge hits alone

have resulted in approx. 20 fatalities (2003-2013) and 75 injuries (2010-2013) per year respectively. Over

height trucks have resulted in ~13,108 structural damage bridge hits in last four years (2010-2013) [4].

Since there is no national database on over-height crashes including all vehicle types, these numbers paint

a very conservative picture of the magnitude of the problem. More conclusively, a 2011 survey of State

Department of Transportation (DOTs) in U.S. revealed that 68% (30 out of 44 State DOTs) consider

bridge hits to be a significant problem. New York State alone has reported ~200 bridge hits /year with

many bridges being repeatedly hit in last few years [5]. Internationally, Ireland (>180 hits/year), United

Kingdom (>2,000 hits/year) and 14 European Union Member states including Western Australia and East

Japan Railway consider bridge hits to be significant safety risk [6].

Factors contributing to bridge hits include; wide disparities in penalties for over height violations

[7], variance in standard bridge clearances between National and off-National Network, different over-

height permit requirements between States, anecdotal reporting of bridge clearances (actual/under-

4

reporting), driver ignorance regarding vehicle/cargo height, lack of route planning by haulers, use of

consumer grade GPS [5], drivers not following authorized routes [8] and inadequate low clearance

warning signs [9]. In U.S., State DOTs have identified “over-height trucks” as prime cause of bridge hits.

Once an over-height vehicle is en-route towards a low clearance bridge, OHVDs are usually the last line

of defense to prevent the bridge hit from occurring.

State of Practice OHVDs

The typical set up for current OHVDs (Figure 2) consist of an aligned optical transmitter and a

receiver unit mounted on poles (A) on opposite sides of the road at the required detection height. The

transmitter emits a light beam across the road width which is continuously detected by the receiver. As an

over-height vehicle passes through, it obstructs the light beam, which triggers the receiver to activate the

warning sign/VMS (B) and alarm bell (C) to alert the driver. Once an over-height vehicle is detected, the

driver can be instructed (using VMS) to stop or take an exit before the structure. The warning sign/VMS,

alarm bells are typically placed 100-150 feet after the detectors (A). The system is designed to work at

highway speeds (75mph) and is installed much before the structure (up to a quarter mile) to accommodate

approach to suitable exits or to allow a safe stopping distance to the structure.

A review of 16 OHVDs systems from 11 different companies (across U.S., U.K, Canada,

Germany, Australia) revealed that this operational set up is used across the world which is exactly similar

to the first reported OHVDs in 1965 [11]. Improvements to the basic set up have been limited to (i)

modifications in the light source (visible red/Infrared/laser), (ii) light modulation (visible), diffuse,

reflective or opposed mode operation (infrared), (iii) using single, dual beam or Z-beam systems [12].

Figure 2. Detection concept of State of Practice OHVDs [10]

Limitations of State of Practice OHVDs

Since these systems are installed up to a quarter mile before the bridge, many times power &

communication lines have to be brought up to the installation site. A communication cable between the

transmitter and receiver units requires digging a trench across the road leading to roadway closures &

traffic delays [13]. Associated structural & electrical installation costs are usually much higher than

detector costs. ITS grade installation has been reported to cost between $50,000 -$100,000 per approach.

The stand alone cost of detector–pair (A) itself is very high ($9,000-$25,000 per approach). Because of

such high system costs, installations are limited to critical locations. State DOTs have reported these

OHVDs to suffer from alignment issues due to ground heave and false detections due to vehicle antennas,

5

flying debris, birds and snow deposits on vehicle. Rain, snow and sunlight during certain hours of the day

have also been reported to cause false positives [5]. Most times, the drivers miss the only warning sign

(C) while some do not hear the alarm bell (B) (while listening to radios, etc.). There is no further line of

sight signage to stop them from hitting the bridge. Also, utilizing expensive VMS/matrix signs ($20,000-

$70,000) for regulatory messages adds heavily to the system cost.

Proposed Solution: LaRa- OHVD

The LaRa detector is designed to be installed on the face of the structure (e.g. bridge) being

protected itself. The detector uses a standard freeway sized warning sign with flashing yellow beacons

which are also installed on the bridge face next to the detector. Since most bridges already have power

(street lights), this results in minimal installation cost. LaRa combines LADAR, optics and traffic

engineering principles to detect an incoming over-height vehicle at safe stopping distance from the

bridge. The infra-red laser based device is eye safe and low cost, satisfying the performance requirements

of state of practice OHVDs.

Detection Concept of LaRa- OHVD

The LaRa detector is mounted in the center of the roadway, above the bridge clearance height; on

the bridge face itself, pointing towards the oncoming traffic. The detector transmits a sheet of laser light

covering the road width at a distance greater than the safe stopping distance to the structure. The top view

of the installation is shown in Figure 3.

Figure 3. LaRa –OHVD (Top view)

Figure 4. Vehicle detection zones and height measurement

Pre-defined vehicle detection zones are established before the safe stopping distance to the bridge

and LaRa continuously checks for vehicle presence in these zones using LADAR technology. Once a

vehicle is detected, La Ra measures height from top of vehicle to sensor as shown in Figure 4. If vehicle

height is less than bridge clearance, then LaRa discards the measurement. If the vehicle height is more

than the bridge clearance then the vehicle is detected in the large and over-height detection zones (Figure

6

5). As “Measured height” decreases than “Fixed install height”, the over-height vehicle is confirmed.

LaRa then activates the yellow traffic beacons installed next to the warning sign “OVER HEIGHT

VEHICLE STOP WHEN LIGHTS FLASH” mounted on the bridge itself. As soon as over height vehicle

is detected LaRa can communicate with transportation/emergency agencies through a suitable interface.

Figure 5. LaRa over height detection and proposed driver warning system

Advantages of LaRa- OHVD

LaRa is unique it is operation. It is first OHVDs in the world which is installed on the bridge

being protected and features long range detection (> 1000 feet). It detects vehicles travelling at highway

speeds and provides a broad detection zone instead of single optical beam. Existing OHVDs often utilize

inductive road loops to confirm vehicle presence leading to higher installation/system costs. LaRa

employs vehicle detection zones and algorithms to detect vehicles and minimize false alarms (due to

flying debris, birds), a significant advantage over the beam-break approach used in conventional OHVDs.

The total system cost (including detector, warning sign/beacon, installation) is minimal compared to

conventional OHVDs enabling mass deployment. A unique advantage is the line of sight warning system.

Since the warning sign and traffic beacons are installed on the face of the structure, drivers can always see

them and they are hard to miss. This eliminates the need for expensive VMS/Matrix signs or alarm bells

reducing cost and simplifying installation. LaRa can measure vehicle speed and predict if collision is

imminent. This provides crucial seconds for agencies to plan pre-emptive emergency recovery and

response. Also, LaRa continuously measures the vehicle height in detection zones and can provide a very

useful collision statistic for the responding agencies to assess the legal vehicle over-height. LaRa can also

reduce the level of structural damage for an over speeding driver as he responds to the warning sign and

hits the structure at a reduced speed (while braking).

LaRa –OHVD Prototype Construction

Currently, the device is in its design stage and a prototype is being assembled for testing. Figure

8 shows the prototype and the typical test setup. For demonstration purposes, the warning sign is

excluded and only a single traffic beacon is considered.

7

Figure 8. LaRa-OHVD prototype (Left) and test set-up (Right).

Conclusions

Existing OHVDs are limited in deployment and operational features. By combining a mature

vehicle detection technology (LADAR), state of art optics and existing traffic engineering guidelines; a

cost effective LaRa-OHVDs is proposed. LaRa is envisioned to detect over-height trailers, trucks and

large sized loads which cause the maximum number of bridge hits (94 %) in New York State [5].

Expected limitation is the requirement of a straight approach road up till the safe stopping distance to the

protected bridge. With respect to New York State, majority (78%) of bridge hits have been found to occur

on State Highways, Parkways and Interstates which can provide such site characteristics [5]. With LaRa

OHVD currently under development, actual field testing will be required to validate the system

performance. However, the low cost design, minimal installation and features like broad vehicle detection

zones, algorithms to minimize false detections, line of sight warning sign advantages, speed & over height

measurement; makes the LaRa OHVDs an innovative concept in over height detection. By facilitating

mass deployment, LaRa has the potential to protect thousands of our bridges to prosperity; save lives,

save tax payer’s dollars and contribute to the vital infrastructure preservation goals in the United States.

Bibliography

1. U.S. Department of Transportation, Federal Highway Administration, Bridges and Structures (2015),

Inspection, NBI, Deficient bridges by State and Highway System, Accessed 14th April 14th, 2015

http://www.fhwa.dot.gov/bridge/deficient.cfm

2. Carson, J.L. (2008), Commercial Motor vehicle Size Enforcement. NCHRP Project 20-07, Task 254,

Vehicle Size and Weight Management Technology Transfer and Best Practices. National Cooperative

Highway Research Program, Transportation Research Board

http://onlinepubs.trb.org/onlinepubs/archive/NotesDocs/20-07(254)_SizeEnforcement.pdf Accessed

May 1st, 2013

3. Get the Most Effective Low Clearance Alert System for the US. Low Clearance GPS Data, 2008.

www.lowclearances.com. Accessed May 15th, 2013

4. National Highway Traffic Safety Administration, Fatality Analysis Reporting System,

http://www.nhtsa.gov/FARS Data obtained through special request.

5. Agrawal, A.K., Xu. X. and Chen. Z. (2011), Bridge Vehicle Impact Assessment, Final Report, Project

# C-07-10, University Transportation Research Center, New York State Department of

Transportation, New York. https://www.dot.ny.gov/divisions/engineering/technical-services/trans-r-

and-d-repository/C_07_10_final%20report.pdf

6. Byrne, A. (2009), Special Topics Report- Railway Bridges in Ireland and Bridge Strike Trends.

Railway Safety Commission, Dublin, Ireland. http://www.rsc.ie/publications/railway-bridges-in-

ireland-bridge-strike-trends/ Accessed Aug 7th, 2013

8

7. Fu, C.C. (2001). Maryland Study, Vehicle Collision with Highway Bridges. Contract No. SP907B1,

Maryland State Highway Administration, The Bridge Engineering Software and Technology Center,

Department of Civil Engineering, University of Maryland.

8. Parkway Truck Restrictions, Parkways Truck Regulations Brochure. (2009), New York City

Department of Transportation.

9. Martin, A. and Mitchell, J. (2004), Measures to Reduce the Frequency of Over-Height Vehicles

Striking Bridges: Final Report, Unpublished Report, PPAD9/100/61, Department of Transport, U.K.

10. Trigg Industries (2013), Detection Concept, Trigg Industries Inc.

http://www.triggindustries.com/overheight-vehicle-detection-systems/application-notes/detection-

concept.html

11. Trigg Industries (2013), About Us, Trigg Industries Overheight Vehicle Detection,

http://www.triggindustries.com/about-us.html

12. Sinfield, J. V. Synthesis Study: Development of an Electronic Detection and Warning System to

Prevent Overheight Vehicles from Impacting Overhead Bridges. Publication FHWA/IN/JTRP-

2009/30. Joint Transportation Research Program, Indiana Department of Transportation and Purdue

University, West Lafayette, Indiana, 2010. doi: 10.5703/1288284314276.

13. Trigg Industries (2013), Z-Pattern Design Notes, Trigg Industries Inc.

http://www.triggindustries.com/overheight-vehicle-detection-systems/application-notes/z-patternr-

design-notes.html