640Inductive Loop Vehicle Detection Systems

640.01 Description. This work consists of furnishing all component materials required

to form complete independent vehicle inductive loop detection systems as specific herein. This includes assembling, constructing, testing, and installing same in conformity with these specifications to ensure properly operating units in accordance with the design or as directed.

640.02 Materials. Materials shall include shielded cable, vehicle loop assemblies and

loop detector amplifiers and shall conform to the requirements of this Section.

640.02.1 Conduit. Conduit shall be in accordance with Section 637.

640.02.2 Inductive Loop Detection System. Inductive Loop Detection System shall

consist of the following principal components: two (2) or more turns of insulated loop wire wound in shallow slot sawed in the pavement, lead-in cable from the curbside pull box to the intersection controller cabinet, and an electronics unit housed in a nearby controller cabinet. The functions intended for use with this system include Vehicle Detection and Data Collection – special detection.

640.02.2 1--Loop Detector Wire. Loop detector wire shall be cross-linked polyethylene

insulated loop detector wire rated at 600 volts that meets the requirements of IMSA Specification No. 51-3.

640.02.2 2--Loop Detector Lead-In Cable and Shielded Cable. Loop detector lead-in

cable shall be shielded cable conforming to IMSA Specification No. 50-2, for polyethylene insulated, polyethylene jacketed Loop Detector Lead-in Cable. Unless otherwise indicated, the cable shall be AWG # 14, 2-conductor or AWG #18, 4-conductor.

640.02.2 3--Sealant. Sealant material shall be a polyur ethane sealant conforming to the

requirements herein. The material shall be manufactured specifically for this use and shall be used in accordance with the manufacturer's instructions. The material shall be dielectric, have no detrimental effect on cable insulation, and bond to either portland cement or bituminous concrete paving with minimal shrinkage. The material shall, when cured, retain flexible characteristics and accommodate movement associated with portland cement and bituminous concrete pavements. The material shall not track in hot weather and shall be suitable for applying when the surface temper ature is between 50°F and 130°F. The material shall be resistant to the effects of weather, vehicular abrasion, motor oils, gasoline, antifreeze solution, brake fluid, and deicing chemicals normally encountered. The polyurethane sealant shall be a one-part moisture curing compound requiring no mixing or application of heat prior to or during installation. The sealant shall meet the following additional requirements. Properties Requirement Test Procedure Viscosity (uncured) 30,000 cps ASTM: D 1048 (B) Tack-Free Time (uncured) 24 hrs., maximum ASTM: D 1640 Hardness, Shore A (cured) 85 ASTM: D 2240 Elongation (cured) 250% ASTM: D 412 Tensile Strength (cured) 500 psi, minimum ASTM: D 412 Packaging Minimum Shelf Life Liter Ply Packs 9 Months Five Gallon Containers 12 Months If deemed necessary during the review process, the Engineer may require the Contractor to submit manufacturer’s certification to meet the above requirements.

640.02.2 4--Loop Detector Amplifiers. Loop Detector Amplifiers shall be rack-mounted,

digital, solid-state, self-tuning inductive loop detector cards with extend and delay output features. The Loop Detector Amplifier Card shall have the following minimum features and operational requirements.

640.02.2 4.1--Tuning. The amplifier card shall tune automatically upon the application of

power in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.20.

640.02.2 4.2--Modes of Operation. Each amplifier card channel shall be capable of

functioning in both presence and pulse mode in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.17.

640.02.2 4.3--Sensitivity Control. Each channel of the amplifier card shall meet NEMA

TS2 2003 v02.06 Section 6.5.2.15 requirements for sensitivity controls.

640.02.2 4.4--Crosstalk Avoidance. The amplifier card shall be capable of preventing

crosstalk between channels of the same unit in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.23.

640.02.2 4.5--Outputs. Each output device shall conform to NEMA TS2 2003 v02.06

Section 6.5.2.26 requirements.

640.02.2 4.6--Controls and Indicators. All amplifier card controls and indicators shall

be in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.25.

640.02.2 4.7--Self-Tracking. The amplifier card shall automatically accommodate after-

tuning changes in the loop/lead-in in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.21.

640.02.2 4.8--Detection of Continuous Traffic Queues. Each amplifier card channel

shall provide unlimited detection of continuous traffic without loss of detection in long peak-hour traffic queues. Vehicle movement over the loop shall re-start presence hold time.

640.02.2 4.9--Built-in Noise Rejection Circuitry. The amplifier card electronics shall be

adequately protected from transient voltages and currents which may occur on both power lines and loop leads.

640.02.2 4.10--Loop Detector Amplifier Tests. Each amplifier card shall conform to the

performance requirements set forth in NEMA TS2 2003 v02.06 Section 2.8.

640.02.2 4.11--Channel Labeling. A space for labeling each channel shall be provided

on the front of each detector card. Each channel shall be labeled with its associated phase.

640.02.2 4.12--Delay and Extension Timing. When called for in the plans, the amplifier

card shall contain the necessary electronics to provide delayed call and extended call operation. Timing shall be digital and selection of delayed, extension or normal detector operation shall be accomplished via front panel control. Delay and Extension timing shall be settable on a per channel basis with the timing programmed independently. Detector card delay timing capabilities shall be provided in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.24.1. Detector card extension timing capabilities shall be provided in accordance with NEMA TS2 2003 v02.06 Section 6.5.2.24.2.

640.02.2 4.13--Communications. The amplifier card shall be equipped with a front panel

RS232 serial port for transmission of data.

640.02.2 4.14--Software. The detection device shall be provided with vendor PC software

necessary to completely configure the detector sensor and accessory devices. The software shall be capable of operating on a PC operating system using the communication ports on the detector card(s). The software shall pr ovide access to read or change configuration settings, fault identification, monitor real-time activity, and to retrieve traffic data, if present. Vendor supplied PC software for interfacing w ith the amplifier card shall be capable of displaying loop system operating characteristics on a per channel basis, including collecting and sorting speed, volume and occupancy data from each channel.

640.03 Construction Requirements . The Contractor shall install, configure, and

demonstrate a fully-functional Vehicle Detec tion System as shown in the plans. The Contractor shall install all equipment according to the manufacturer’s recommendations.

640.03.1 Inductive Loop Detection System Installation.

640.03.1 1--Loop Detector Amplifier(s). Each loop detector amplifier shall be mounted

in the cabinet card rack.

640.03.1 2--Saw Cuts. A chalk line or equivalent method shall be used to outline the

perimeter of the loop on the pavement and routes for lead-in cables. The saw cut in the pavement shall not deviate by more than one (1) inch from the chalked line. All saw cuts shall be cleaned, free of any dust, dirt, or other debris and completely dry prior to installation of the loop wire, loop wire twisted pair lead, or lead-in cable. There shall be no cutting dust, grit, oil, free water or other contaminants in the saw cut. Loop wire shall be installed in saw cuts in the roadway made by a diamond or abrasive power saw. The slot width and depth shall be as indicated in the plans; however, in all cases the slot shall be of sufficient depth to provide for a minimum of 1-inch cover between the top of the loop wires and the roadway surface. The saw cuts shall be overlapped so that the slot has full depth at all corners. All corners where loop wires turn shall be diagonally cut so that there are no jagged edges or protrusions that may damage the wire. Where possible, the loop assembly shall be placed prior to the final surface lift of asphalt. Where lead-in cable is required to pass through the curbside, it shall be installed in ¾-inch rigid steel conduit. Saw cutting through the curb shall not be permitted.

640.03.1 3--Loop Wire. All loops shall be wound in a clockwise manner and the first turn

of the loop wire shall be placed in the bottom of the saw cu t, with each subsequent turn placed on top of the preceding turn. The loop wire shall be pushed to the bottom of the saw cut with a non-metallic tool which will not damage the insulation. The clockwise “lead” of each loop shall be tagged and identifie d. Alternate polarity shall be used on adjacent loops. The hold down material shall be non-metallic, placed in the saw slot using segments one (1) to two (2) inches long, spaced 12 inches apart, and the distance from the top of the hold down material to the final surface of the roadway is not less than 1½ inches. Loop wire shall not have any cuts, nicks, abrasions or breaks in the insulation before or after installation in the slot. Any wire having defects in the insulation shall be replaced at Contractor's cost. Loops shall have sufficient turns of loop wire to conform to the following tables unless the manufacturer of the loop detector being used specifically recommends different inductance values. Loop location and configuration shall be as shown on the plans unless otherwise directed. Rectangular Loop Inductance (µh) for 3 Turns Loop Size (feet) W x L @ f = 1 kHz @ f = 20 kHz @ f = 40 kHz @ f = 60 kHz 6 x 6 74.46 74.39 74.28 74.25 Rectangular Loop Inductance (µh) for 2 Turns Loop Size (feet) W x L @ f = 1 kHz @ f = 20 kHz @ f = 40 kHz @ f = 60 kHz 6 x 20 83.80 83.71 83.59 83.59 6 x 30 117.66 117.58 117.57 117.83 6 x 40 151.48 151.47 151.72 152.49 6 x 50 185.28 185.41 186.12 187.75 Quadrapole Loop Inductance (µh) for 2 Turns Loop Size (feet) W x L @ f = 1 kHz @ f = 20 kHz @ f = 40 kHz @ f = 60 kHz 6 x 50 421.56 425.01 436.39 457.72

640.03.1 4--Loop Sealant. All saw cuts with the wire installed shall be inspected and

approved by the Department designee before the sealant is installed. The Contractor shall install the sealant in strict adherence to the manufacturer’s recommendation and these specifications. No sealant shall be installed during inclement weather or under any condition that might introduce moisture into the saw slots. The viscosity of the sealant shall be such that it can be readily poured into the slot, completely surround the wires, displace all air and fill the slot so that the sealant is flush with the roadway surface. The finished sealed slot shall be waterproof and present a neat workmanlike appearance. The sealant shall be sufficiently hardened before allowing traffic on it.

640.03.2 Shielded Cable. Shielded cable from the loop lead-in to the detector amplifier

shall be of one continuous length and installed in conduit or aerially supported on messenger cable and spliced to the loop lead-i n wires in the pull boxes or equal weather- tight enclosures. All splices in pull boxes shall be carefully made to ensure constant low resistance and shall be insulated by means of a waterproof splice. The loop lead-in shall be spliced to the shielded cable using butt splice crimp connectors. The connectors shall then be coated with a waterproof adhesive. Each splice shall then be separately wrapped with an all- weather electrical tape and a self-bonding electrical tape. Finally, both splices shall be wrapped together with an all-weather electric tape and coated with a waterproof adhesive. Shielded cable shall be solidly fastened with ring lugs to the terminal strip in the detector equipment cabinet or controller cabinet. Both ends of the shielded drain wire shall be cut off flush and waterproofed so as to not come in contact with the pull box or ground. All work performed shall present a neat and workmanlike appearance. Installation of shielded cable in conduit or aerial shall comply with applicable provisions of Section 637.

640.03.2 1--Splicing. Loop wire, including twisted pair loop wire, shall be one continuous

length of wire with no splices. There shall be no splices in the shielded cable unless otherwise directed by the Engineer or shown on the plans.

640.03.2 2--Terminations. Lead-in cables or twisted pair loop wire shall be terminated

using insulated terminal lugs on a terminal strip, which is located in the controller or detector cabinet. A calibrated ratchet type crimping tool shall be used to attach the lugs to the conductors of the lead-in cable or twisted loop wire.

640.03.2 3--Loop Assembly Identification. Loop lead-in wires or shielded cable

terminating in controller cabinets, detector cabinets or pull boxes shall be uniquely identified by an insulated, waterproof tag. Identification shall indicate the lane and the direction of traffic it detects.

640.03.2 4--Inductive Loop Detector Testing and Turn-on. After the loop wire, and

lead-in have been assembled in place and before sealing the saw slot, a continuity check and a resistance check on the loop to ground shall be made. Resistance to ground shall be not less than 10 megohms. This same test shall be made after the slot is sealed. An inductance test in the presence of the Department designee shall also be made to ensure that the required inductance values are achieved. After installing shielded cable to the loop lead-in, the same tests as required for the loop and loop lead-in shall be performed for the shielded cable shall be performed for the shielded cable.

640.04 Method of Measurement. Vehicle Loop Assembly and Shielded Cable will

be measured by the linear foot computed horizontally along the saw slot, regardless of number of turns, in which the loop wire or shielded cable is installed and will not include the loop lead-in to the pull box. The length of the loop lead in to the pull box will be considered incidental and absorbed in the vehicle loop assembly. Loop Detector Amplifiers will be measured as a unit per each.

640.05 Basis of Payment. Vehicle Loop Assembly and Shielded Cable, measured as

prescribed above, will be paid for at the contract unit price per linear foot, which price shall be full compensation for furnishing all materials, drilling and/or sawing, installing, sealing, connecting lead-ins, testing, all equipment, tools, labor and incidentals necessary to complete the work. Loop Detector Amplifiers, measured as prescribed above shall be paid for at the contract unit price for each. This price shall be full compensation for furnishing all materials; for all drilling and/or sawing; installing; sealing; connecting lead-in; testing; and for all equipment, tools, labor and incidentals necessary to complete the work. Payment will be made under: 640-A: Vehicle Loop Assembly - per linear foot 640-B: Shielded Cable, AWG __, ___ Conductor - per linear foot 640-C: Loop Detector Amplifier * - per each * Additional information may be indicated