Work Zone - 8.07 Mobile Operations
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8.07 Mobile Operations
Maintenance operations which involve non-vehicular encroachment on lanes other than those immediately adjacent to the median or outside shoulder are not considered mobile operations, and should be reviewed by the appropriate traffic and safety representative, to determine what traffic control typical should be utilized to perform the work.
The following in table 8-2, are examples of Mobile Operations:
Table 8-2: Mobile Maintenance Activities
| Activity | Intersections |
|---|---|
| Approach Sweeping | Shoulder, and minor non-vehicular encroachment in traveled way |
| Expressway Patrol | Shoulder and/or occupy a lane |
| Freeway Lighting | Occupy lane, continuously mobile ≈ 5 mph |
| Curb Sweeping | Example |
| Catch Basin Clean-out | Example |
| Litter Pickup | Example |
| Vegetation Control | Example |
| Routine Blading | Example |
| Gravel Shoulder Maintenance | Example |
| Shoulder Spot Seal Patching (kettle) | Example |
| Shoulder Bituminous Patching | Example |
| Patrol Patching | Example |
| Pavement Marking | Example |
8.07.01 Adequate Sight Distance
For maintenance operations, adequate sight distance is the length of roadway that the driver can see and is greater than or equal to the stopping sight distance. See Table 8-3 for the stopping sight distances.
Table 8-3: Stopping Sight Distance as a Function of Posted Speed Limit
| Speed (mph) |
Distance (ft) |
|---|---|
| 25 | 155 |
| 30 | 200 |
| 35 | 250 |
| 40 | 305 |
| 45 | 360 |
| 50 | 425 |
| 55 | 495 |
| 60 | 570 |
| 65 | 645 |
| 70 | 730 |
| 75 | 820 |
8.07.02 Shadow Vehicles
A shadow vehicle should be used for lane closures on all roadways which have a 45 mph or greater posted speed, and two or more lanes in each direction.
A shadow vehicle may be used in other work zones as deemed necessary. Factors to be considered in determining need include the following:
- Time of day of the closure
- Seasonal variations in traffic volume
- Length of lane closure and anticipated duration
- Traffic speeds
- Frequency of traffic stopping/turning movements
The shadow vehicle should be parked with the brakes set, and the front wheels turned away from traffic and work area if possible, or as specified by the engineer.
The roll-ahead space is the distance between the front of the shadow vehicle and the work area. Whenever a shadow vehicle is used, this additional space is required and is determined based on the weight of the shadow vehicle.
8.07.03 Mobile Attenuators
Mobile Attenuators (MA) refer to truck mounted attenuators (TMA) and trailer mounted attenuators. These devices should be considered for use when maintenance operations are conducted where the posted speeds are 45 mph or greater; where personnel and/or equipment occupy a lane customarily used by traffic.
Refer to the temporary traffic control typicals for proper placement of the mobile attenuator, typicals numbered in the 4400s and 5400s. In a traffic control operation the mobile attenuator vehicle should be the first vehicle encountered by the motorist. Please note that some operations require more than one mobile attenuator. The number of mobile attenuators required is based on the number of lanes closed. An additional mobile attenuator may be used on the shoulder of urban freeways. Additional guidance on the proper placement of mobile attenuator may also be found in the manufacturer’s documentation and/or as directed by the maintenance supervisor or local TSC traffic representative.
The use of a mobile attenuator does not eliminate or reduce the requirement for the correct application of traffic control devices and measures outlined in this manual.
8.07.04 Truck Mounted Attenuator Applications
The following are examples of mobile attenuators used in projects to protect personnel or equipment:
- The vehicle is designated as a protective vehicle (shadow vehicle or barrier vehicle) as part of the maintenance of traffic typicals, maintenance of traffic plans, or other contract documents.
- Mobile attenuators are not intended to be used for the removal, installation or maintenance of traffic signals due to the uniqueness of the area that needs to be protected at an intersection.
- Mobile/short duration operations such as pavement marking convoys, grinding in rumble strips, permanent sign installation, luminescent installation, etc.
- Aerial work is being performed on scaffolding, lifts, hoists, bucket trucks, etc., where workers using this equipment are on the shoulder not protected by temporary barrier for longer than 15 minutes in duration.
Mobile attenuators must not be mounted on the vehicle or equipment used by personnel to complete aerial work. The use of a mobile attenuator should be considered for other operations depending upon the level of worker exposure. Engineering judgment should be used to determine the appropriate form of TTCD to complete the work on every project.
Mobile attenuators may not be used as a barrier ending except during the replacement of a damaged barrier ending. When a mobile attenuator is used as a temporary safety measure for a damaged barrier ending; it may only be used for a maximum of 48 hours or as approved by the Engineer.
8.07.05 Equipment Requirements for Truck Mounted Attenuator
All TMAs used must meet or exceed the requirements of NCHRP 350 test level 2 (TL-2) or test level 3 (TL-3), or MASH TL-2 or TL-3 as described below for work zone traffic control devices.
- TL 2 may be used on non-freeway roadways with a normal posted speed of 40 mph or less. Test Level 2 TMAs are prohibited for use on all roadways with posted speed limits of 45 mph or greater.
- All TMA rated for NCHRP 350 – Test Level 3 may be utilized on all roadways regardless of the posted speed limit.
The face of the TMA that is visible to approaching traffic must have reflectorized alternating yellow and black chevron stripes sloping downwards in both directions from the center of the attenuator.
When operating a MA, ensure the following is performed, as per the manufacture’s recommendations:
- Ensure the height from the bottom of the mobile attenuator to the roadway surface is 12 inches (+/- 2.5 inches) and within manufactures specifications.
- Ensure the mobile attenuator is parallel (level) with the roadway surface.
- Provide a shoulder harness and headrest for the operator of the MA vehicle.
- Ensure material loaded on vehicle to obtain the gross weight is securely attached. Materials that will be off loaded and incorporated into the construction activities will not be considered part of the vehicle gross weight.
For stationary operations, ensure the attenuator vehicle is in second gear if it has a standard transmission and park if it has an automatic transmission. With the parking brake set, turn the front wheels away from traffic and work area if possible, or as specified by the engineer. Keep any and all blades on the vehicle raised. Ensure there is enough roll ahead distance between the vehicle and the work area.
Exhibit 8-3: Mobile Attenuator
INSERT PICTURE
The required gross vehicle weight must be as shown in the Tables 8-4 and 8-5. The attenuator device must not be mounted on a lift vehicle that is used in an aerial maintenance operation.
Table 8-4: Guidelines for Rolle-Ahead Distance for Mobile Attenuator Vehicle Test Level 2
| Weight of Mobile Attenuator Vehicle (Minimum) | Post Speed (mph) (Posted Speed Prior to Work Zone) | Roll Ahead Distance* (Distance from the Mobile Attenuator Vehicle to Work Area) |
|---|---|---|
| 5.5 Tons (Stationary Operation) | 40 or less | 25 feet |
Table 8-5: Guidelines for Roll-Ahead Distance for Mobile Attenuator Vehicle Test Level 3
| Weight of Mobile Attenuator Vehicle (Minimum) | Post Speed (mph) (Posted Speed Prior to Work Zone) | Roll Ahead Distance* (Distance from the Mobile Attenuator Vehicle to Work Area) |
|---|---|---|
| 5 Tons (Mobile Operation) | 60-70 50-55 45 |
175 feet 150 feet 100 feet |
| 12 Tons (Stationary Operation) | 60-70 50-55 45 |
50 feet 25 feet 25 feet |
