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 workspace, but not so close as to have the protective vehicle pushed ahead into the workspace 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 many tractor trailers) will determine the roll-ahead distance to be used. Adding ballast to increase the weight of the protective vehicle will decrease the roll-ahead distance and should be considered on facilities with a population of commercial motor vehicles.
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.
A barrier vehicle is for stationary work operations to protect workers on foot in the roadway from errant vehicles. A large dump truck, a large rack truck or other vehicle having a gross weight of at least 24,000 pounds shall be used as Barrier 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. 2-way radios should be used to communicate between the Protective Vehicles when available.
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 in Incident Management, Mobile and Short Duration operations. Signs shall not obstruct visibility of any lights (taillights or warning lights) or sideview mirrors on the Advance Warning Vehicle.
Advanced Warning Vehicles may be occupied or un-occupied.
If occupied, communication must be established with the work vehicle to ensure adequate spacing is maintained as the work progresses. The operator shall remain in the vehicle with the safety belt and headrest properly adjusted. The vehicle must be positioned parallel to traffic and have the wheels aligned with the lane striping, and to maintain lane discipline and to stay in lane if struck.
If unoccupied, the vehicle must be positioned parallel to traffic and have the wheels aligned with the lane striping.
It must be placed in Neutral with the parking brake set (Park / 2nd gear for engine off conditions).
If the vehicle encroaches into the travel lane on any type of road or stays entirely on shoulder on any high-speed road 45 MPH or higher, it then becomes a Barrier/Shadow Vehicle and shall be equipped accordingly.
Truck / Trailer Mounted Impact Attenuator (TMIA)
Impact attenuator, also known as a crash cushion, or crash attenuator, is a device intended to reduce the damage to structures, vehicles, and motorists resulting from an errant motor vehicle collision. Impact attenuators are designed to absorb the colliding vehicle's kinetic energy. TMIA can be mounted on Truck or Trailer.
- 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 24,000 pounds.
- TMIAs meeting NCHRP 350 Test Level 3 are acceptable until they can be replaced by units meeting MASH Test Level 3, pursuant to AASHTO / FHWA Joint Implementation Agreement for Manual for Assessing Safety Hardware (MASH) dated January 7, 2016.
- Where the posted speed limit is 45 mph or less, the TMIA may be a Test Level 2 attenuator. Where the posted speed limit is more than 45 mph, a Test Level 3 attenuator must be used.
- Barrier vehicles may be loaded with sand, gravel or fine aggregate to enhance the vehicle’s gross weight.
- All items mounted on or in the cab of the support vehicle shall be adequately secured as not to become a projectile in the event of an impact.
Barrier Vehicle and TMIA are required if speeds are 45 mph or greater. Barrier Vehicle is required and TMIA is recommended if speeds are less than 45 mph.
For short duration / mobile applications:
- The Shadow Vehicle (and Advance Warning Vehicle(s) where appropriate) shall maintain the appropriate Roll-Ahead Distance, positioned parallel to traffic, parking brake set when possible, have the wheels aligned with the lane striping and lane to maintain lane discipline and to try to stay in lane if struck. Operators of Shadow Vehicles and Advance Warning Vehicles shall remain in the cab, with the lap/ shoulder belt and headrest properly adjusted.
For stationary applications for more than an hour:
- The Barrier Vehicle (and Advance Warning Vehicle(s) where appropriate) shall maintain the appropriate Roll-Ahead Distance, be an unoccupied truck, positioned parallel to traffic, parking brake set, placed in 2nd gear (Park / Neutral), have the wheels aligned with the lane striping and lane to maintain lane discipline and to stay in lane if struck.
All work vehicles within the work zone must be equipped with an approved flashing warning beacon meeting or exceeding the values of SAE Class 2 Warning Lights. NYSDOT vehicles adhere to the NYSDOT Vehicle Lighting Standard meet this requirement. Consider site distances and proximity to workers when positioning work vehicle.