Work zone traffic control manual, Study notes of Workplace Safety

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• Revised Feb

Introduction

Work Zone Traffic Control

The purpose of work zone traffic control is to provide a safe work area for workers within the roadway, while facilitating the safe and orderly flow of all road users (motorists, bicyclists and pedestrians including persons with disabilities in accordance with the Americans with Disabilities Act of 1990) through the work zone.

This manual is intended to provide New York State Department of Transportation (NYSDOT) employees, utility companies, municipalities, and contractors who are involved with the design, set-up and maintenance of highway work zones, or anyone working within the state right-of-way, with the basic principles and elements constituting a safe work zone. The information presented in this manual is based on the requirements set forth in the National Manual of Uniform Traffic Control Devices and the NYS Supplement, review of work zone manuals from a selection of state and federal agencies, and discussions with members of the NYSDOT Work Zone Traffic Control Committee.

This manual includes basic information on work zone traffic control, including a description of traffic control devices, illustrations of acceptable, commonly used devices, and the proper flagger attire and methods. Color diagrams (typical applications) depicting typical traffic control set-ups for two-lane and multilane highways are intended to show the minimum requirements for a safe work zone set-up. Traffic control or protection can be enhanced for situations that may require additional measures such as high traffic or pedestrian volume, high speeds, restricted sight distance, poor or confusing alignment.

This is a “living document” that will evolve as recommendations are received from the Regions. Work zone traffic control diagrams will be added, and deleted, as necessary, and all will be posted on the NYSDOT internet site (Work Zone Traffic Control Manual).

Please address any questions, comments, and/or recommendations regarding this manual to Charles Riedel 518.457.2185 or MD Haque 518.457.7784. Office of Traffic Safety & Mobility, NYSDOT.

Taper Length Criteria for Work Zones

The five types of roadway tapers (or transitions) used in work zone traffic control are the following:

1. Merging Taper (L) - When a lane is closed and vehicles in that lane must merge with traffic in an adjacent lane.
2. Shifting Taper (L/2) - When there is a lateral shift in the path of the lanes, but there is no reduction in the number of travel lanes.
3. Shoulder Taper (L/3) - When the shoulder is closed to traffic.
4. One-lane, Two-way Taper - When one lane of a two lane, two-way roadway is closed to traffic and where alternate one-way operation in one lane is in effect.
5. Downstream Taper - When transitioning traffic back to the normal traveling conditions.

L = Taper length in feet W = Width of offset in feet S = Posted speed limit, off peak 85th^ percentile speed prior to work starting or the anticipated operating speed in mph

FORMULAS FOR DETERMINING TAPER

Speed Limit ‘S’ (mph) (^) Taper Length ‘L’ (ft)

40 mph or less L=WS(S) 60

45 mph or more L=WS

Buffer Spaces

The buffer space is a crucial safety feature of a work zone. It serves to separate traffic flow from the work area or potentially hazardous area and provides recovery space for an errant vehicle. In the past, buffer spaces (both longitudinal and lateral) were an optional feature in NYS work zone traffic control. However, in NYS a longitudinal buffer space is no longer optional in most cases. A few exceptions have been made depending on the type of work operation and the use of protective vehicles. If there is any question as to whether a buffer space is required for a specific operation, please contact the DOT Regional Traffic Engineer. Neither work activity nor the storage of equipment, vehicles, or material shall occur in this area. A lateral buffer space may also be used to separate passing traffic from the work area. Its use and width is based on conditions at the work site.

LENGTH OF

LONGITUDINAL BUFFER SPACE

“B”

BASED ON TABLE 6C-2 FROM THE NMUTCD

Speed (mph)

Distance (ft)

30 200 35 250 40 305 45 360 50 425 55 495 60 570 65 645 70 730

Note: Use posted speed limit if 85th^ percentile is unknown

Protective Vehicle Area and Roll-Ahead Distances

Proper placement of protective (shadow/barrier) vehicles is essential during all types of operations. The vehicle must be placed close enough to the operation to prevent motorists from intruding into the work space, but not so close as to have the protective vehicle pushed ahead into the work space if hit from behind. This distance is known as the roll-ahead distance. The weight of the protective vehicle, the speed of traffic, the speed of the work operation, and the vehicle make-up of the traffic stream (all passenger vehicles or a large number of tractor trailers) will determine the roll-ahead distance to be used. The roll-ahead distances shown on our typical applications use a 24,000 lb protective vehicle and a 15,000 lb impacting vehicle.

There shall be no equipment, vehicles, or workers within the roll-ahead area.

Types of Protective Vehicles

There are two types of protective vehicles: Barrier and Shadow

Barrier Vehicle: A barrier vehicle is for stationary work operations to protect workers on foot in the roadway from errant vehicles. The barrier vehicle is unoccupied with the parking break set and front wheels turned away from oncoming traffic and employees in the work area, if possible. A barrier vehicle does not require a Truck Mounted Impact Attenuator (TMIA) in all cases. If a TMIA is used, it shall be attached to a large dump truck, a large rack truck or other vehicle having a gross weight of at least 24, pounds. Where the posted speed limit is 55 mph or less, the TMIA shall be a Test Level 2 attenuator. Where the posted speed is more than 55 mph, a Test Level 3 attenuator shall be used, if available. Barrier vehicles may be loaded with sand, gravel or fine aggregate to enhance the vehicle’s gross weight.

Shadow Vehicle: A shadow vehicle is for mobile operations only. The shadow vehicle shall be equipped and meet the same size and weight requirements as a barrier vehicle. The driver shall remain in the vehicle and adjust the vehicle’s spacing as work progresses.

Advance Warning Vehicle: This vehicle is stationed a considerable distance in advance of a moving or stationary maintenance operation. Its purpose is to display sign messages which will advise motorists of what to expect ahead. If the vehicle is able to stay completely on the shoulder, a pick up truck may be used. However, if the vehicle encroaches into the travel lane, it then becomes a Barrier/Shadow Vehicle and shall be equipped accordingly.

Computed Roll-Ahead Distances for Protective Vehicles

BARRIER VEHICLE

STATIONARY OPERATION

Vehicle Weight (lb)

Prevailing Speed (mph)

Weight of Impacting Vehicle To Be Contained (a)

4,500 lb 10,000 lb 15,000 lb 24,000 lb 10,000 60 - 65 50 Ft. 100 Ft. 150 Ft. 200 Ft. 50 - 55 25 Ft. 75 Ft. 100 Ft. 150 Ft. 45 or less 25 Ft. 50 Ft. 75 Ft. 100 Ft. 15,000 60 - 65 25 Ft. 75 Ft. 100 Ft. 150 Ft. 50 - 55 25 Ft. 50 Ft. 75 Ft. 100 Ft. 45 or less 25 Ft. 25 Ft. 50 Ft. 75 Ft. 24,000 60 - 65 25 Ft. 50 Ft. 75 Ft. 100 Ft. 50 - 55 25 Ft. 25 Ft. 50 Ft. 75 Ft. 45 or less 25 Ft. 25 Ft. 25 Ft. 50 Ft.

Notes: (a) Weights of typical vehicles: mid-size auto, 2,250 lb; full-size auto 3,500 lb; loaded ¾-ton pickup truck, 6,000 lb; loaded 1-ton cargo truck, 10,000 lb; loaded 4-yard dump truck, 24,000lb. (b) N/A (c) Values suggested as the appropriate buffer distance for vehicles equipped with TMIAs.

Source: J.B. Humphreys and T.D. Sullivan, “Guidelines for the Use of Truck-Mounted Attenuators”, Proceedings of the Symposium on the Work Zone Traffic Control, Federal Highway Administration, June 1991

Work Area Duration

Work duration is a major factor in determining the number and types of devices used in work zone traffic control areas. As a general rule, the longer the operation will last, the more traffic control devices are needed.

Mobile Work : Work that moves intermittently or continuously. Examples: Placing cones and/or signs for stationary work zones Herbicide spraying Sweeping operations Paint striping operations Placing traffic counters Mobile work zones provide the lowest level of traffic control and safety and should only be used where the work at any specific location will be completed within 15 MINUTES. There may be cases where site specific conditions justify longer duration use of mobile work zones to minimize the exposure of traffic and the workers to each other. In such cases, an exception may be approved by responsible person(s) designated by the region after consideration of relevant factors such as speeds, sight distance, staging of the work, degree of obstruction to traffic, traffic volumes, and the relative severity and duration of exposure to workers and traffic.

Short Duration: Work that occupies a location for up to 1 hour. Examples: Placing traffic counters Re-lamping traffic signals/ streetlights Pot hole Repair Minor guiderail repair Sign Repair Due to the short work time, simplified traffic control set-ups are allowed to reduce the hazards of traffic exposure to workers. Careful consideration of traffic and roadway conditions must be given to each work zone prior to selecting the most appropriate traffic control set-up. Shoulder work and work on low speed, low volume roadways may only require a single warning sign, cones, and a flagger, while a high speed, high volume road would require a more detailed lane closure utilizing more safety control devices such as a barrier vehicle, signs, channelizing devices and a flashing arrow panel.

Short-Term Stationary: Daytime work that occupies a location for more than 1 hour within a single daylight period. Examples: Guiderail Repair Bridge Inspection/Repair Ditch Maintenance Concrete Roadway Repair

Short term stationary work areas are typically occupied by materials, equipment and workers, but the work area is cleared at the end of the work day and normal traffic flow restored. Traffic control typically includes signs on portable supports, cones or drums

Advance Warning Signs

All work zone signing (ground or truck mounted) shall conform to the NMUTCD and NYS Supplement. Special conditions or emergencies may require additional signing. Refer to the MUTCD and the NYS Supplement for guidance on the proper location, message, spacing, sequence, mounting height and size of signs used for traffic control.

Materials Rigid and flexible “roll-up” signs may be used for mobile, short duration and short term stationary work. Rigid signs must be mounted at least 5 feet above grade ( feet where there are pedestrians or parked cars) for visibility and to avoid windshield penetration if they are impacted. Flexible signs must be mounted at least one foot above grade. Mesh signs shall not be used. Use retro reflectorized rigid signs for night work because they present a flat, uniform reflective surface. Sign stands/posts must meet NCHRP 350 crash testing standards. Ex: Breakaway posts and hinges..

Installation All signs should face at approximately right angles to on-coming traffic and be as close to vertical as possible to avoid reflecting sun glare into the driver’s eye. In mobile and short duration work zones, signs may be mounted on vehicles. Orange flags can be mounted on warning signs to enhance their visibility.

Credibility Signs shall be maintained, clean and with the legend fully intact. They shall remain in place only when needed. Signs which do not reflect actual conditions promote driver disobedience of all signs and therefore should be covered, removed or turned away so they are not visible to traffic in any travel lane. Sign covers must be opaque, and cover the sign face completely. Partially visible signs may divert attention away from traffic and other devices.

If unneeded signs are to be stored at roadside, try to store them out of the clear zone or as far from traffic as practical. If stored close to traffic, lay the signs flat and fold up the legs of the sign supports.

Where operations are performed in stages, only use those devices that apply to the conditions present during the stage in progress. Signs set up over a long distance should be periodically checked.

Guidance for Proper Signing

• Install one or more work zone warning signs whenever the work results in a changed condition which may require a higher level of driver caution. One sign (usually “Road Work Ahead”) may be adequate for minor changes such as removed guide rail, removed edge line or roadside work which does not encroach on the shoulder or travel lane. Use “Road Work Ahead” as the first sign in a warning sign series on minor side roads where distance information is not necessary. Use more signs as the impact on traffic increases. For work which obstructs traffic, a 3 sign series is typical. The first sign is a general warning sign to get the motorist’s attention. The second sign warns of the specific condition and the third sign advises the driver of any action to be taken.
• General warning signs such as “Road Work XX Ft” should be limited to the first sign of a series. Subsequent warning signs in that series should identify specific conditions. Use signs shown in the MUTCD/WZTCM for lane and shoulder closure, alignment and intersection signs, flagger and worker symbol signs, road closed, detour, etc.
• Location of advance warning signs should consider exiting and entering traffic. Advance posting distances indicated in the MUTCD and WZTCM are starting points and should be adjusted as appropriate for site specific conditions. Avoid starting a warning sign series upstream from a major exit or intersection, except when it is desirable to divert traffic off the route at that point or where the intersection is within 1000 feet of the work site.
• Where single advance warning signs are provided on ramps or minor intersecting roads, the “Ahead” wording rather than a specific distance is preferred because it is easier to adapt to site conditions and reduces sign inventory needs.
• Warning signs must be located to provide adequate visibility distance to drivers; not blocked by foliage, roadway features, or other signs and traffic control devices; and not located where glare from light sources behind the sign may reduce visibility. Actual distance from a warning sign to the condition should be close to the stated distance on the sign, but accuracy should not be at the expense of sign visibility.
• Signs must be adequately spaced to provide time for the driver to read each one. Sign spacing varies with the type of highway and the prevailing speeds and is specified in the MUTCD and WZTCM. See Advance Warning Sign Spacing Table on the next page for details.

Flashing Arrow Panels

• Arrow panels are traffic control devices used for additional advance warning and where a lane is closed and traffic must merge with traffic in an adjacent lane. They are generally used for lane closure, and slow moving maintenance activities. Use flashing arrow panels for all lane closures on highways where the posted speed limit equals or exceeds 45 mph.
• The arrow display should NEVER be used on two-lane, two-way roads. Arrow displays should only be used where traffic can be moved to another lane without danger of meeting on-coming traffic…multi-lane, single direction roadways.
• The four corner flash mode may be used to provide additional advance warning where an arrow display is not appropriate. THE FLASHING BAR DISPLAY IS NOT PERMITTED.
• Locate arrow panels to maximize the distance between the arrow panel and the point where drivers first must see and understand the arrow. Provide at least ½ mile legibility (more if possible) for highways with speed limits of 45 mph or greater. Trailer mounted arrow panels should be 4 feet high by 8 feet wide, mounted at a height of 7 feet. Provide at least 1500 foot legibility if used where speed limits are below 45 mph.
• For stationary lane closures, place the arrow panel on the shoulder inside the taper near the beginning of the taper. Avoid placing it near ramps, median crossovers, and intersections where it may confuse drivers. Use only one arrow panel for each stationary lane closure. Too many arrow panels can encourage drivers to change lanes unnecessarily.
• For mobile maintenance activities where a lane is closed, an arrow panel must be placed in the closed lane at the rear of the activity. If possible, use two arrow panels for mobile/moving work zones; one on the first shadow vehicle in the closed lane, and the second on a shadow vehicle, pick-up truck or trailer on the shoulder upstream of the first one. The arrow panel should be placed on a vehicle separate from a work vehicle and positioned between the last work vehicle and approaching traffic.
• In areas of restricted sight distance, it may be necessary for the arrow panel vehicle to lag behind or stop and wait behind the activity to maintain optimal visibility to approaching traffic. As sight distance improves behind the activity, the arrow panel vehicle should close the gap. However, the distance between the arrow panel vehicle and the work activity should be kept short enough to discourage drivers from re-entering the lane.