902.19 Construction Inspection Guidelines for Sec 902

From Engineering_Policy_Guide
Revision as of 10:05, 18 January 2012 by Smithk (talk | contribs) (902.13 Construction Inspection Guidelines for Sec 902 moved to 902.19 Construction Inspection Guidelines for Sec 902: Per Traffic and CM, revision to bring policy into substantial compliance with the 2009 MUTCD.)
Jump to navigation Jump to search
Slot Cutting as discussed in Sec 902.13.2

General (Sec 902.2)

Installation of traffic signals can be considered, for the most part, as erecting, installing, and wiring of specialized equipment to control flow of vehicular and pedestrian traffic. Types of control equipment currently specified vary greatly in their makeup and in necessary associated equipment. The type of control equipment specified for a particular project is based on geometrics of the intersection, anticipated volume of traffic that will use the facility, and proximity of other intersections.

Regardless of the type of control equipment specified or geometrics of the intersection involved, construction procedure is approximately the same for all signal projects. The order of work consists of: (a) laying or pushing conduit network; (b) excavating, forming, and placing of pullboxes, post bases, and controller bases; (c) erection of signal posts; (d) installation of electrical service; (e) installing signal heads; (f) installing detectors; (g) pulling cable into conduits; (h) tagging and wiring signal heads, detectors, interconnection system, and controller; (i) checkout of individual components and final checkout of the entire system. It is the intent of this article to set out inspection procedures in the same general order as work is usually done.

Type A and Type B post bases

The inspector assigned to a signal project should thoroughly study the contract. If the inspector has had no previous signal work, they can gain much by study of a previously completed installation. Discussions with Traffic are very helpful. They can explain the various types of equipment to be used and give the inspector a better understanding of nomenclature used in signal work.

The list of equipment and material that the contractor submits for approval serves the same general purpose as does the list for highway lighting. See Sec 901.2.


Staking and layout work for a traffic signal project should be done with the idea always in mind to avoid conflicts with roadway items, and with signing and lighting if they are included in the project. Each signal post location shall be staked and carefully checked to see that signal heads to be mounted thereon will be in clear view from the lane, or lanes, to be controlled. Posts should not be located in sidewalks if it can be avoided without reducing visibility of signal heads. Pullbox, conduit runs, and controller base locations may have to be shifted to avoid conflict with other items. Care should be taken to avoid placing signal appurtances in a drainage ditch. If necessary, shift the controller base to a location where chances of its being struck by a vehicle are reduced to a minimum. If the controller base is so situated that it cannot be moved it may be necessary to place a section or more of guardrail around the controller to provide adequate protection.


In the event that some questions arise, the district traffic personnel will be able to clarify any questions. Terminology will vary slightly from manufacturer to manufacturer but the general concept remains the same.

Installation Of Posts And Signal Heads (for Sec 902.5)

Before erection of posts and hanging of signal heads, the inspector is to check equipment for shipment damage. The inspector is to also check the numbers of the various items to see that they agree with the numbers on the previously approved list. Inspect posts for plan dimension and signal faces for plan diameter and the arrow and pedestrian lens for compliance with standard drawings. Check for correct clearances of Types C, CL, BL and B signal posts from overhead power lines.

Signal heads attached using pipe nipples manufactured by the pole company, requiring the pole company to have specific measurements for the placement of the signal heads. Pipe nipples do not allow for adjustment in the field.
Signal heads attached with cable brackets, reducing manufacturing costs and allowing field adjustment.

Signal posts with Type S and Type T signal heads must be erected in a vertical position by adjustment of leveling nuts. Signal posts for span wire installations are to be raked (leaned) approximately 3 in. away from the bracket arm.

Signal heads as well as arrow signal lenses are to be installed in final position with vertical edges and lines plumb and horizontal edges and lines true, as checked with a spirit level. An otherwise satisfactory installation can give an unsightly appearance if signal heads are canted from plumb or arrow lenses point in a slightly different direction from plan.

After signal heads have been wired and power is supplied to the controller cabinet, signal faces should be aimed and focused. All signal indications should be verified by applying momentary power to each field wire termination at this time. Signal bulbs are supplied by Traffic. They are to be placed in the socket so that the open part of the filament points upward. This simple procedure will greatly increase the lamp life.

An optically limiting signal head is used when it is necessary to limit the visibility zone to specific lanes and areas. Manufacturer’s instructions for installation will provide enough data for an inspector to check this type of signal head properly.

Sometimes louvers are used to limit the visibility of specific indications. The louvers are to be installed and oriented according to the plans.

The current specifications allow the contractor to utilize either die cast aluminum signal housings or those made of polycarbonate material. Since polycarbonate housings are less costly and lighter in weight, most contractors are providing the plastic housings, visors, backplates and in some cases, lenses.

Since polycarbonate signal heads are lighter in weight than the aluminum type, the mast arm type signal post tends to vibrate more under windy conditions. For this reason the inspector is to check all connections, both electrical and mechanical, to ensure all are tightened securely.

Power Supply Assembly (for Sec 902.9)

Refer to Sec 901.

Service Pole Installation (for Sec 902.9.1)

This item of work is usually done while underground conduit is being installed. Location and arrangement of equipment on the service pole is to be cleared with the supplying utility. Conductor cable that supplies power to the controller is to be tested for shorts and grounds after installation. This procedure is to also check incoming secondary voltage for design tolerance of plus or minus 5 percent voltage drop. Generally, 120-volt service is supplied to the controller cabinet.

Traffic Controller Assemblies (for Sec 902.11)

Types Of Controllers

Solid State Fixed Or Pre-timed Controllers. In some instances, a pre-timed controller is used as a semi-actuated controller. This is accomplished by installing loop detectors in a left turn lane or a side street approach. A vehicle entering the zone of influence of the loop will cause the pre-timed controller to display a 3- or 4-second yellow to the phase having the green light and then the side street or the left turn traffic is allowed green time to clear the intersection. Depending upon whether the intersection is operating in an isolated manner or is interconnected to a system, the side street or left turn green will be given fairly soon depending upon the status of the controller.
The accuracy of time settings on solid state controllers is very high since their time base is established from the 60 hertz incoming power frequency. All models have a battery back up so that the timing memory and other programs are not lost in the event of AC power failure.
Solid state pre-timed controllers use the keyboard entry method of establishing timing functions. A display enables the inspector to see the amount of time allotted for each particular function. These controllers also have interconnection features allowing them to be monitored in a system by a solid state or electromechanical master controller. In order to prevent unauthorized people from changing any timing on this type of equipment, access to the keyboard is denied until a coded sequence of access numbers are first entered in the keyboard.
Solid state, pre-timed controllers use solid state load switches to control the intersection signal lamps. A fail-safe monitor is also required to prevent conflicting indications from being displayed and detect other failures.
Pre-timed Solid State Master Controllers. This type is a special controller generally used to supervise one or more electromechanical pre-timed controllers, solid state pre-timed controllers and actuated solid state controllers. When specified, this controller may: effect a transfer from one timing plan to another at local controllers; establish time offsets between local controllers so that traffic may progress through a series of intersections with minimum delay; provide for railroad, fire, or emergency vehicle pre-emption; provide a regularly scheduled program for local controllers to follow on a week to week basis; and other features.
The inspector should ask the contractor to demonstrate each of the master controllers’ specified functions. If local controllers are in operation and traffic is using the intersections, the master controller checkout is to be made during off-peak traffic periods.
Pre-timed, Solid State Master Controllers. This controller may supervise one or more electromechanical pre-timed controllers, solid state pre-timed controllers and many actuated or solid state controllers. Coordination between the master controller and local controller may be accomplished by multi-conductor cables, telephone voice grade wire pairs or by utilizing time based coordination.
Solid State Actuated Controllers. Timing for these controllers are entered by keyboard. All signal lamp load switches are also solid state. Our specifications require a fail-safe device known as a conflict monitor. This monitor is hardwired into the output side of each load switch and when a load switch failure occurs the signals are switched into flashing operation immediately.
The inspector can determine by observing the controller display what interval is being timed, detector calls coming in, next phase waiting for the right of way and other information. Some controllers have a digital read-out showing a countdown of the time remaining in any particular interval. The monitor program card shall be checked prior to signal turn on for proper configuration. The inspector is to have the contractor check the operation of the conflict monitor by momentarily shorting two conflicting green indications together at the point where they are terminated in the bottom of the controller cabinet. A word of caution here - use an insulated jumper wire and try to select a period of light traffic in order to cause a minimum of inconvenience to motorists.
All conflict monitors have indicating lights to show when they are in operation and they also have a reset button which reactivates the controller into normal operation. The inspector is to check traffic flow in the intersection before pushing the reset button because when the controller reverts from flashing it returns to normal signal operation.

Auxiliary Control Equipment

In addition to the previously mentioned controllers, there are several types of auxiliary control equipment which are specified to increase efficiency of the main control equipment, provide for railroad and emergency vehicle pre-emption and other special functions.

902.13 train.jpg

Railroad, Fire And Emergency Vehicle Preemption Equipment

This equipment, when actuated by any one of the above units, presents a signal sequence favorable to the emergency vehicle and also protects other vehicular traffic in the intersection. The fire or emergency vehicle pre-emption switch is usually located in a nearby fire station or at city hall. Activating the switch will initiate a pre-empt sequence in the effected controller. Setting of pre-emption time depends upon the time it will take for an emergency vehicle to clear locally controlled intersections. This is best determined from an actual test run by an emergency vehicle.

In certain cases where a railroad crossing is near a signal installation, the pre-emption equipment is placed in operation when detectors installed on the tracks are actuated by an approaching train. Cooperation with the railroad company is needed for checking these systems. The inspector is to check the signal sequence during the preemption cycle to see that yellow clearance intervals are displayed before signals turn red and that signals operate so as not to trap vehicles on the tracks.

Controller Installation

General. Regardless of type of control equipment specified for a particular project, certain procedures are common to all installations. Controller installation consists of the following separate operations:

(1) Identification and tagging of all incoming cables
(2) Placing controller housing on concrete base or wood pole
(3) Stripping the jacket from each cable and identifying each conductor
(4) Cutting, grouping, splicing and terminating of incoming conductors to controller terminal strip
(5) Termination of incoming power supply
(6) Checking of all detectors
(7) Final checking of the entire system.

During these phases of work the inspector is to check tagging of cables for specification compliance. All signal head cables are to be terminated in a horizontal terminal strip located at the bottom of the control cabinet. Every terminal connection is to be checked to see that conductors are held firmly in place. The inspector is to insist that conductors leaving the conduit are bunched and laced up neatly before they are fanned out to terminal strips. It is the contractor’s responsibility to make proper terminal connections. The contractor is to check each conductor to determine if it is connected to the proper terminal before the system is placed in operation. The inspector is to become familiar with the various circuit diagrams to gain a better understanding of the work involved.

After the contractor has finished his conductor terminations the inspector shall require incoming conduit or conduits to be sealed in accordance with specifications. This sealing operation is important in case an underground gas leak occurs near the intersection. There have been cases where gas accumulation in the controller housing has been ignited by arcing of relays. The resulting explosion usually causes extensive damage to the controller and its housing.

The inspector is to check that all housing vents are free of obstructions and properly screened. If a ventilating fan is specified, the inspector is to ascertain that it operates when the cabinet temperature reaches approximately 90 degrees F.

Actual controller installation does not entail much work after cabinet wiring has been completed. It consists, in most cases, of placing components upon racks or shelves in the cabinet and plugging in the units to pre-wired cable connectors. This arrangement simplifies maintenance replacement of controllers and their components.

Detector Installation (for Sec 902.13)

The purpose of any vehicle detector is to sense the passage or presence of a vehicle approaching an intersection and relay this information to the controller for processing. It is the purpose of this article to explain briefly the theory of each type of detector and proper installation techniques. Proper location of detectors is important and if there are any questions consult Traffic.

Induction Loop Detector (for Sec 902.13.2)

Induction loop installation

This type of detector is based on the theory that the cable embedded within the roadway acts as a tuned antenna. The cable is tuned to the resonant frequency of a frequency in the amplifier cabinet. When a vehicle enters the loop area, a resultant shift in the loop voltage phase with respect to frequency of the amplifier places a detection call in the controller. On resur-facing projects when new loops are to be installed be sure the old loop is destroyed by cutting through the loop wire to prevent it from providing false calls.

The location of traffic signal loop detectors and the location of the stop bars at intersections are critical. Improper location of these two features in relation to each other can cause operational problems with the traffic signals. Ideally, the two features are located so that when a vehicle stops at the stop bar, the stopped vehicle is fully in the detection zone of the loop. Care also needs to be taken when side street left turns are present. Locating the stop bars too far forward in these situations can either make it difficult for the side street traffic to execute their left turn or the turning traffic could clip the loop, thereby putting a false detection into the signal.

When intersection markings using durable materials, such as the 3M tape, are to be installed at intersections with traffic signals, the installation sequence of the detector loops and permanent pavement marking is important. Coordination of the layout of stop bars and loops with traffic personnel is encouraged for proper placement of both. The detection loops should be cut and sealed first, followed by placement of the stop bars. This sequence is recommended so that the durable pavement marking tape is not cut or damaged by the saw cutting process for the detector loops. The grooving required for installing the tape must not damage the loop detectors, since the loop cuts are significantly deeper than the grooving. Following these steps will provide the good, clean look that MoDOT desires on projects and will allow the tape to provide the expected durability.

Installation of the loop detector begins with sawing a slot in the pavement. This saw cut is to be made by wet cutting. If the slot crosses an expansion joint, depth must be increased slightly to provide a little play in the cable for expansion. Placement of loop slots across cracks and joints must be avoided if at all possible. Before cable is placed in the slot, all debris and moisture must be removed. The cable is then placed in the slot and pushed into proper position by use of a blunt nonmetallic object. The roadway loop cable is spliced to a twisted shielded two conductor cable in the nearest junction box or pullbox by means of a “poured” splice. Before the pavement slot is filled, a resistance test is required. A minimum 10 megohm resistance to ground reading at the controller cabinet is necessary. Following a satisfactory resistance test the sawed slot is filled with sealing compound. Ensure the loop does not float up while sealing. The lead-in cable between the loop and detector amplifier shall be twisted at least three turns per foot.

Methods for tuning and operation of the induction loop detector vary among manufactur-ers. Therefore, manufacturer’s operating instructions are to be followed.

Push Button Detectors

This type detector is a simple, manually operated switch mounted on the signal post. It permits pedestrians to call for right of way at a traffic actuated controlled intersection. Installation of these detectors is well covered on standard drawings and in specifications. To check this type of detector when the controller system is initially placed in operation, the inspector is to ensure that pushing the button places a call in the controller in the proper phase. The inspector also ensures the pre-set time (walk) plus the pre-set clearance (flashing don’t walk) interval is displayed on the pedestrian signal heads.

Microwave and Ultrasonic Detectors (for Sec 902.13.3)

For these types of detectors follow the recommendations of the manufacturer.

Pull and Junction Boxes (for Sec 902.14)

The inspection of excavating, forming and placing concrete for pullboxes or aprons and the various types of bases should be done in a manner similar to that set out in Sec 901.12. The inspector must also make certain that conduits are properly capped, and that ground rods and anchor bolts stay in proper position during concrete placement. Adequate vibration of the concrete is necessary to fill all voids. The contractor is required to protect anchor bolt threads during concrete placement. All concrete is to be removed from any signal equipment including threads immediately after finishing has been completed.

In addition to instructions in Sec 901.12 for pullboxes, it is important to ensure that pullboxes drain properly. The standard drawing depicts two types of pullbox drains. If a Type I drain is used, ensure that the proper depth of stone is used. If it becomes evident that, due to the nature of soil or due to the elevation, a particular pullbox will not drain properly, it may become necessary to provide a tile drain in lieu of the stone drain provided on plans.

Conduit Systems (for Sec 902.16)

Conduit runs are generally graded a minimum of 0.5% for drainage. If a long conduit run will have a flat grade between two pullboxes, and it is not possible to lower the grade on either end, the conduit should be “humped” in the middle to drain in both directions. A typical case where it is very difficult to grade conduit runs properly is where a conduit has to be jacked or pushed beneath an existing roadway with a rocky subbase. Even if the contractor bores a pilot hole and comes out on the opposite side at approximate line and grade required, it is possible that the conduit will “snake” enough that a low point will exist in the run.

Installation Of Conductor Cable (for Sec 902.19)

Measuring, cutting to proper length, and pulling of conductor cable into conduits and handholes, even though a slow and laborious process, will be carefully inspected. Strict specification enforcement is necessary to prevent cable damage. Insulation resistance tests to detect shorts and grounds are not required except in installation of power cables; however, it is to the contractor’s advantage to make such tests with an ohmmeter or multimeter as they are checking for continuity and tagging circuits. Items are to be checked to see if they agree with the products list approved.

The inspector ensures the contractor uses red, orange and green color-coded wires for like colored signal faces on the main artery or street. This will help the contractor in circuit identification at the controller. It will also help in future maintenance work. The inspector also requires the white conductor in each cable to be a neutral or common return.

Test Period (for Sec 902.21)

Controller Checkout

Certain procedures should be followed in testing a controller before acceptance. If the installation is to be placed in operation under traffic, it is suggested that the local police force be asked to have at least one officer present during testing of a controller, unless otherwise provided in the contract. Arrangements should be made with Traffic to paint lane markings, directional arrows, and stop lines at the intersection before placing signals in operation if not provided in the contract. Also, if the controller operates satisfactorily and is to be left in operation, certain regulatory signs are to be removed. Most district traffic personnel have considerable experience in signal operation. They can be of invaluable service in helping to set up initial controller timing and in checking controller operations when it is placed in service.

If district Traffic personnel are not available when the controller is to be placed in operation, there are definite procedures to be followed by the inspector to assure that the controller functions in accordance with the contract. Starting with the simplest type of controller and progressing to more complicated types, this article will outline briefly adjustments to be made and functions to be expected. Existing signals are not to be removed until the new signals have proven to operate properly.

If the intersection has been previously used by traffic, there will often be signal violations during the first few days of operation. The trial time setting may be incorrect, causing undue delay to one phase. If this occurs, the inspector asks the contractor to change the cycle split to provide more time for the congested phase. Traffic personnel should be consulted when timing changes are required.

Check-out of a traffic actuated signal system should be performed, if the intersection is open to traffic, with assistance of police officers during an offpeak traffic period. If the intersection is not open to traffic, check-out may be performed using one or more test vehicles. If the intersection is open to traffic, detector operation is to be checked before turning on signal indications. Detector amplifier settings are to be adjusted for proper coverage so vehicles passing through the detector’s coverage will cause positive relay action at the controller. After this has been done to the inspector’s satisfaction, timing should be set on the controller.

When the inspector is sure the controller, detectors and auxiliary equipment are operating properly and timing is approximately correct, the inspector will have the contractor turn on the signal indications when there is a lull or gap in traffic. The inspector checks all signal face indications to see that they are displayed in plan sequence and are aimed properly to direct traffic. During this time the inspector watches traffic movements to see whether the controller is timing movements so there is minimum congestion.

If a particular phase seems to be delaying traffic and causing congestion, the inspector will advise maintenance and traffic personnel for timing changes. It is recommended that district traffic personnel be involved in signal turn on and semi-final inspection of the project.

Closed loop signal systems require additional system checks.