Questions and Answers: About Crash Testing of Work Zone Safety Appurtenances
Updated May 22, 2002
(These questions and comments are from State transportation agencies, industry, and the Federal Highway Administration.)
General | Channelizing Devices | Signs | Barriers | Crash Cushions and Truck Mounted Attenuations | Other
1.0 QUESTION: Acceptable Crash Test Vehicles - I have talked with some crash test agencies and they say that there crash test would be done with a Ford Festiva. Is this acceptable? If not what is?
ANSWER - Ford Festivas and Geo Metros are both acceptable vehicles. I believe the last ones manufactured
are both outside of the recommended age range in NCHRP Report 350 but FHWA
has agreed that the old ones may continue to be used as test vehicles until
the weight of the small car is formally changed by TRB.
1.1 QUESTION: Turnaround Time for Acceptance Letters - Once the Office of Safety receives our crash test report how long does
it take to receive a letter of acceptance?
ANSWER - Our backlog is down to about a two-month turnaround (as of May 2002).
1.2 QUESTION - What is the procedure for getting an acceptance on a device that is similar to one already accepted, without doing additional crash testing? Can I just "certify" that my device is similar to the accepted device?
ANSWER - This depends on whether you are copying a "generic" design or one that is the property of the company that paid for the crash testing. Any manufacturer or vendor can replicate the "generic"
Type II and Type III barricades
that are covered in Acceptance
Letters WZ-45 (September 15, 2000) or WZ-85 (November 15, 2001) and use
these Acceptance Letters. The testing of these devices was paid for with public
funds (or permission was granted to distribute the design). The manufacturer
or vendor must certify their barricades substantially conform to the generic
designs, and the devices will be crashworthy.
For devices crash tested at the expense of a private company, a vendor may
use the acceptance letter written to the company that had the devices tested
only if they: (a) purchase the devices from the company that paid for the
testing (or another authorized distributor), or (b) obtain permission from
that company to reproduce their design.
1.3 QUESTION: Traffic Control Devices Placed Below Grade- What can you do if you have to place a traffic control device where it is
located below the grade of the pavement? We are replacing damaged joints and
slabs on a concrete roadway, and there isn't enough room to locate the signs,
barricades, or drums on the pavement adjacent to traffic. There are also long
sections where the entire shoulder pavement has been removed. Can we modify
crash tested devices and place them in the excavated areas?
ANSWER - In these situations where it is important that the traffic
control device not appear to be "down in the hole" you can modify
the crashworthy device so that the sign panel, barricade panels, or drum face
appear as if it were at a normal elevation. For example, if a six inch thick
shoulder pavement has been removed and you want to place a Type III barricade
there, it is acceptable to extend the barricade uprights by six inches so
that the horizontal rails can appear to be at the proper elevation. Similarly
you may stack drums so that it appears that the drum base is at the elevation
of the pavement. Although we might expect that the crashworthy traffic control
device may not perform in exactly the same way it did when it was crash tested
on level terrain, the fact that a vehicle is running into the excavation is
likely to be a worse problem than is the impact with a traffic control device.
By using a crashworthy device modified for the situation, we are providing
an appropriate level of safety.
1.4 QUESTION - Was public input involved in adopting the provisions
of National Cooperative Highway Research Program ( NCHRP) Report 350 for the
ANSWER - The public was involved through a formal rulemaking
process that culminated in a final rule in the July 16, 1993, Federal
Register. In that notice, the FHWA added NCHRP Report 350 at paragraph
625.5(a)(13) of Title 23, Code of Federal Regulations (23 CFR). Since then,
the "Guides and References" section of 23 CFR, Part 625, under which
the NCHRP Report 350 was cited, has been removed. The NCHRP Report 350 is
now cited in Section 16, Paragraph (a)(12) of the Non-Regulatory Supplement
to the Federal-aid Policy Guide, Subchapter G, Part 625 (NS 23CFR 625).
The rulemaking process involved publishing the proposed rule and receiving
public comments on the proposed rule.
The July 16, 1993, Federal Register stated that
contingent upon the results of ongoing research and service performance evaluation,
the FHWA anticipated that approximately five years after the adoption of NCHRP
Report 350 all new installations of traffic barriers and other roadside safety
features on NHS projects would be only those that have been judged to meet
the testing and evaluation criteria in Report 350.
Using the effective date of the adoption of that rule would imply an implementation
date of August 16, 1998. By our July 25, 1997, memorandum, "Information:
Identifying Acceptable Highway Safety Features," the FHWA interpreted
this milestone to be the "advertising date" and changed the effective
date to October 1, 1998, to conform to the beginning of the Federal fiscal
On July 1, 1998, AASHTO proposed an agreement on revised implementation
dates for Report 350 hardware including work zone devices. FHWA concurred
with this agreement and has changed the deadline dates for Category 2 and
Category 3 devices. All deadlines regarding work zone traffic control devices
refer to the date by which all newly purchased devices must meet Report 350
criteria. Existing hardware may be used until they meet the end of their normal
The agreed dates are as follow:
Category 1 devices: October 1, 1998
Category 2 devices: October 1, 2000
Category 3 devices, Attenuators: October 1, 1998
Category 3 devices, temporary barriers: New units must have tensile and
moment resistance after October 1, 2000. New units must meet Report 350 criteria
by October 1, 2002.
Category 4 devices. The deadline date has been deferred via a policy memorandum
dated September 13, 2000. An announcement of the implementation schedule for
these devices is expected by October 1, 2003
All new safety features on the NHS covered by the guidelines in the NCHRP
Report 350 included in projects advertised for bids or included in work done
by force-account or by State forces on or after the dates listed above are
to have been tested and evaluated and found acceptable in accordance with
the guidelines in the NCHRP Report 350.
1.5 QUESTION - Why is it necessary to establish the crashworthiness
of work zone appurtenances, since performance of existing devices does not appear
to be a problem? Devices are hit resulting in only minor damage.
QUESTION - The need for the criteria is unclear. Thousands of
devices have been hit and the vehicles have left the scene, so is there really
a problem? There have been no known incidences of a light coming off a sign
and coming through a windshield.
ANSWER - From the results in two States that recently conducted
work zone (WZ) accident studies, we know that the severity of the impacts
with WZ appurtenances is generally what would be expected. That is, the severity
of the crash increases with the mass of the devices impacted. Impacts with
channelizing devices are less severe, those with sign supports more so and
barriers the most. In a soon to be published study of WZ crashes, it was reported
22 of 495 crashes involved signs and similar devices. Two crashes resulted
in injuries requiring hospital treatment. In one, a vehicle struck a portable
sign on the shoulder. The sign broke the windshield , and the driver suffered
internal injuries. In the other, a portable sign blew down, leaning across
a concrete barrier in the travel lane. A vehicle struck the sign, breaking
the windshield, with the driver receiving facial lacerations. In another WZ
crash study, 12 of 589 crashes studied involved Channeling Devices (Barrel),
three of which resulted in injuries.
In summary, there is evidence of a problem. This problem is with devices
that are often placed in the travel way or on shoulders where they can be
easily impacted by errant drivers. There is also technology that can address
the problem at a minimal cost per device. Since we have a cost effective solution
to the problem, we believe we should implement it.
1.6 QUESTION - The supply of crashworthy WZ devices is a concern.
Will the manufacturers of approved products be able to meet the demands throughout
ANSWER - We cannot speak for the manufacturers, but we do not expect
wholesale shortages. If there are spot shortages we will adjust to them. Most
of the WZ channelizing devices are generic so we would expect that anyone
who is willing to enter the market could easily manufacture them. Manufacturers
of portable sign stands have been active in having their devices tested.
1.7 QUESTION - Will the FHWA use the results of tests conducted
by one company to accept similar hardware offered by another, and what makes
one product "similar" to another?
ANSWER - We believe we should not require testing when we have
the information in hand. Therefore, if a product has been shown to be crashworthy
via full scale or bogie testing, other products that are identical or nearly
identical can be assumed to perform in an acceptable manner under impact.
We have accepted certain small sign supports and some recycled plastic guardrail
offset blocks on this basis.
When public agencies sponsor testing, such as Federal Highway Administration
(FHWA) managed research studies or "pooled-fund" crash testing programs,
there is a tendency to focus on "generic" hardware rather than testing
specific proprietary devices. When the occasional proprietary device is tested
under these studies, the results may be examined to see how far they may be
extrapolated to cover other existing hardware.
We agree that there is a question when it comes to determining if a product
is "nearly identical" to a previously tested product. Our assessment
will be made by comparing the design drawings, material specifications, and
the as-tested information on an accepted device with the design details and
the material specifications for a candidate device. When these are not an
exact match, we will evaluate how we believe the differences might influence
the test results and, we will be cautious when the performance of the device
is close to the acceptable limit. This will likely result in our requiring
1.8 QUESTION - It is not economically feasible to replace all
necessary equipment by October 1, 1998.
ANSWER - Knowledge about the availability of crashworthy WZ appurtenances,
including traffic control devices, has been accessible since 1989 in the AASHTO
Roadside Design Guide, and the deadline for safety appurtenances to meet the
requirements of NCHRP Report 350 was published in 1993. Notwithstanding, many
agencies did not feel that they were prepared for this deadline. For this
and other reasons AASHTO and FHWA signed the agreement revising some dates
for implementing work zone traffic control devices . The new dates are listed
in Question 1.0.
1.9 QUESTION - The October 1 deadline refers to what day?
ANSWER - The October 1 dates refers to the advertising date
for contracts and for use by maintenance and force account activities on
1.10 QUESTION - Will data from the pooled - fund study on work
zone devices be made available to the industry?
ANSWER - The member States of the pooled-fund study will be the
first to receive the results of the testing. We will endeavor to provide this
information to the other highway agencies and industry once the pooled-fund
States have been informed. An acceptance memorandum has been issued that covers
devices crash tested to date. It is letter number WZ-40 dated June 6, 2000.
It may be found at http://safety.fhwa.dot.gov/roadway_dept/road_hardware/listing.cfm?code=workzone.
1.11 QUESTION- I had my products crash-tested and I want to put a label on each one to show they are acceptable under NCHRP Report 350. Every state I work in is asking for a different design label or mark or tag. Aren't there any Federal requirements for such a label? (NEW)
ANSWER - The Federal Highway Administration does not mandate any label for crash-worthy devices, but we do want to avoid you having to come up with a different label for each state you work in. In cooperation with the American Traffic Safety Services Association we agree that the following information may be used on a label for any device accepted by the FHWA:
NCHRP Report 350 Compliant - Test Level - ( 2 or 3, depending on what your FHWA letter says)
FHWA Accepted WZ - # # #
The manufacturer's name and/or product identification
This is in line with the ATSSA "Position on the Identification of Crashworthy Traffic Control Devices". We recommend that the states allow you to use any colors, materials, or methods to display this information as long as it provides the information noted above and is in a location and of a size easily readable by an inspector.
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2. CHANNELIZING DEVICES
2.0 QUESTION: Self Certification of Longitudinal Channellizers (NEW) - Can I self-certify road tubes that are affixed to modular curbs?
ANSWER - No. Road tubes
may only be self-certified if they are affixed directly to the pavement. When
they are mounted on top of a modular curb they are considered an entirely
different system that must be shown to be crash worthy. Because these longitudinal
channelizers have no pretext of being a barrier that can redirect
an errant vehicle, the conventional barrier crash test matrix found in NCHRP
Report 350 does not apply. We developed an impact test matrix (in the spirit
of Report 350) with one manufacturer that addressed our concerns. Our first
concern was that the curb could cause errant vehicles to be redirected or
thrown out of control upon impact with the raised separator. Our second concern
was that the individual sections of the modular system might be dislodged
by an impacting vehicle and become airborne and potentially hazardous to other
Four tests were performed using an 820C vehicle to address these concerns.
Travel Test 1A-Vaulting while crossing
At an approach angle of approximately 15°, the car is driven, at 65 miles per hour (MPH), over the separator.
Travel Test 1B - Crossing a Vee in front of an Attenuator
The car is driven, at 65 MPH, across
a 30-degree Vee of separators. (This is an optional demonstration to show
the effect, if any, on the vehicle bumper height as it approaches an impact attenuator.
Travel Test 2 - Vaulting
Approaching the end of the separator,
at a zero degree angle and at 65 MPH, the left front tire is allowed to ride
up onto and along the separator for a distance of 2 meters.
Travel Test 3 - Returning to the proper lane
100 feet of separators are installed in a straight line. The car approaches, at 65 MPH, along the right side of
the separator. The angle of approach is approximately 2°.
2.1 QUESTION: "Simplified"
Crash Testing (NEW) - Our barricade weight is under 45kg does it qualify for simplified crash testing?
What does simplified crash testing consist of?
ANSWER - The simplified
testing that your barricade qualifies for means that only the high-speed test
(100 km/hr) needs to be run, and the test vehicle does not have to be equipped
with accelerometers to determine the occupant impact speed and ridedown acceleration.
However, before and after speeds are needed. Since it is a lightweight barricade
you may wish to have both the head-on and 90 degree impacts done in one test,
as I mentioned while discussing drums above.
2.2 QUESTION: Warning
Lights Mounted on Type III Barricades (NEW)
- I noticed that in the August 28,1998 memorandum that none of the Type III
barricades tested had lights or signs on them. I was wondering why not? When
we test our barricade does it need to have lights "worst case scenario"?
ANSWER - Since August of
1998 some Type III barricades have been tested with signs OR lights, but not
both. I would recommend testing with both in place. Please note that there
have been failures of Type III barricades with conventional aluminum and plywood
signs. I recommend using lightweight sign substrates and lightweight (ie LED
type) warning lights. Visit our website http://safety.fhwa.dot.gov for our
memo "WZ-85" dealing with Type III barricades and other devices.
It should give you some useful information for planning your crash test.
2.3 QUESTION: Crash Test Performance of Drums and Barricades (NEW)
- How should plastic drums and Type III barricades perform during a crash Test?
What would be an acceptable performance? What would be an unacceptable performance?
ANSWER - Conventional plastic drums are Category 1 devices, meaning that formal crash testing is not necessary. The following, from the Questions and Answers page of our website, summarizes the Category 1 process:
"Category 1 devices will be allowed based upon the vendor's self-certification
if the device meets a specification proved safe by crash or surrogate testing,
crash testing, or safe operational performance. The self-certification is
based on an analysis and determination by the vendor that the size, weight,
material and shape are similar to devices proven safe. We expect the vendors
would have an analysis on file to support their self-certification."
Therefore, if you certify that your plastic drum is similar to crashworthy
drums, then testing is not needed. If you wish to back up your analysis with
informal testing it should be conducted with a small car (as close to 1800
pounds as possible) traveling at 100 km/h (62 mph). The car should impact
two drums, one 6 m (about 20 feet) downstream from the other, and turned at
90 degrees relative to the first. If you intend that warning lights be mounted
on the drums then they should be tested that way. Reflective sheeting is not
needed for the tests.
The performance criteria is that the test vehicle should not be slowed by
more than 5 meters per second (this is the same criteria for breakaway sign
posts and will easily be met by a drum), the vehicle should not be thrown
out of control, and no part of the drum or light should cause a hole in the
windshield or intrude into any other part of the passenger compartment. These
are the same performance criteria for Barricades, though a heavy Type III
barricade may actually affect the vehicle's velocity. Also, barricades have
a much greater potential to cause windshield damage than do drums. These two
reasons are why formal testing of barricades is recommended over "backyard
testing." Barricades can also be tested with two being struck during
the same test, however large Type III barricades should be tested individually,
one head-on and one at 90 degrees, because the first barricade may lay across
the test vehicle's windshield and affect the results of the second impact.
2.4 QUESTION: Wood used in Type III barricade rails(NEW) - In crash tested Type III barricades, some used one-inch
thick pine rails, others used 3/4 inch plywood. Some acceptance letters for
generic Type III barricades only specify "wood" rails. What kind of
wood may be used in Type III barricades?
ANSWER - The use of 1x8 pine timber rails should be limited to
barricades no wider than 4 feet. Barricades up to 8 feet wide may use 3/4
inch ACX plywood. Plywood may be used in the wider barricades because it is
generally more flexible than sawn timbers (which are particularly subject
to weakness at knotholes, and tend to splinter more than do plywood rails.)
Four-foot wide barricades are so narrow that they tend to remain intact upon
impact, both in head-on impacts and at 90 degrees. Wider barricades are subject
to breaking apart. Good barricade performance is enhanced if the rails remaining
intact and attached to the uprights. Note that this guidance is only applicable
to Type III barricades that have been found acceptable with "wood,"
"wooden," or "plywood" rails. Other Type III barricades
have only been tested and accepted with aluminum or plastic rails.
2.5 QUESTION - Who is responsible for testing
various combinations of devices such as drums, lights, and flags etc., and which
combination(s) should be tested.
ANSWER - The providers of the traffic control
devices (TCDs) are responsible for the testing of the individual devices and/or
the combinations they are used in. Since lights may detach and impact the
windshield or may remain attached to the TCD and be knocked clear by the vehicle,
it would seem that all parties would benefit from a cooperative effort between
the manufacturers of the TCDs (manufacturers of basic devices and the optional
devices) to determine crashworthy combinations and to have the "worst
case" examples tested.
We appreciate the concerns regarding the difficulty of
identifying "generic" configurations of optional features for crash
testing purposes and the potential costs of testing many alternative designs.
We believe there are a number of options open for reducing the costs of testing,
specifically of warning lights:
- If the light breaks loose from the TCD and impacts the windshield there
must be no penetration of the passengers' compartment. If a relationship
between the size, shape, structure, and mass of the lights and the probability
of the light penetrating the windshield could be established, this could
be used to qualify lights that can be assumed to be less hazardous. Laboratory
testing equipment is available that could launch individual lights into
a windshield. A standard could then be developed for lights that would be
safe regardless of the attachment to the TCD.
- For those lights that fall outside of the crashworthy standard because
of density, mass, or configuration (i.e., sharp corners on the battery pack
or mounting hardware), then a standard attachment specification would be
needed to assure that the light does not come free of the
basic TCD. A crash test of representative TCDs with the heaviest light or
light/battery device firmly attached would then be required. It will probably
also be necessary to demonstrate that a specific TCD has the capability
to "hold on" to the light during an impact. (Recent testing has
shown that relocating the battery assembly to the base of the device yielded
- If a surrogate test can be developed to show that the strength of the
connection of the light to the TCD is sufficient to prevent separation during
impact, this test can be used by the various basic TCD vendors to show that
their device will be acceptable when used with the light. This surrogate
testing should be markedly less expensive than crash testing, and can be
used when minor changes to the geometry or chemical composition of the TCD
are made. The mass of the light must still be significantly less than that
of the drum so as not to alter the center of gravity of the drum casing
it and the light to fly up and damage the windshield.
- Drums with conventional Type A and C warning lights securely mounted
to plastic drums have been moved to Category 1 via our memorandum WZ-54
dated September 15, 2000. It may be found at http://safety.fhwa.dot.gov/roadway_dept/road_hardware/listing.cfm?code=workzone.
2.6 QUESTION -By what date do Category 1 and 2 devices used on projects on NHS highways have to conform to NCHRP Report 350?
ANSWER - ( See Question 1.0 for information
on dates.) Newly purchased Category 1 and 2 devices need to comply
on projects advertised now. Devices that were purchased by the contractor
before October 1, 2000, may continue in use until the end of their normal
service life. Many states, however, are defining the end of that "normal
service live" to be in 2002 or 2003.
2.7 QUESTION - When the Department (State Department
of Transportation) is accomplishing work on NHS highways utilizing our own State
forces, what date do our Category 1 and 2 devices have to conform to NCHRP Report
ANSWER - Standards for NHS routes apply no matter
where the funding comes from or who is doing the work. ( See Question
1.0 for information on dates.)
2.8 QUESTION -FHWA was asked, "Will the
FHWA delay the full implementation of the National Cooperative Highway Research
Program (NCHRP) Report 350 criteria for work zone devices by one- year to October
ANSWER - (See Question 1.0 for information on dates.)
2.9 QUESTION - Will the FHWA maintain a list
of Category 1, 2, 3 & 4 devices that conform to NCHRP 350? We realize that
the FHWA memorandum indicates that no list will be kept for Category 1 devices.
However, we recommend that they do unless FHWA can work with ATSSA to have them
do it. It will be much better and easier for one organization to accomplish
this instead of each individual State having to obtain the self certification
statement from each manufacturer. If the FHWA does not intend to maintain a
list for the other three categories either, we believe that should also be handled
the same way as the Category 1 is handled--by one organization.
QUESTION - We feel frustrated that FHWA hasn't
really looked into the inspection (enforcement) needs of the states. Such as:
how does an individual state (or states) keep an up-to-date listing of accepted
or approved devices such that all industry contractors and subcontractors can
have the same list available for their use?
ANSWER - These questions address concerns with
using self-certification (also called manufacturers' declaration of conformity)
as one of two acceptance processes for Category 1 devices. FHWA chose this
process because the administrative and regulatory burden for FHWA, State and
local highway agencies, and industry is commensurate with the potential low
risk of the devices. Also this process responds to feed back about implementing
the crashworthiness of WZ features that we do not inhibit innovation.
In proposing self-certification, the FHWA is recognizing
an acceptance procedure used in other regulated product sectors for where
level of risk is low. It is believed that this level of assurance will adequately
address safety and impose the least costs on industry and consumers.
FHWA will maintain lists of Category 2, 3, and 4 devices
but we will not keep a list of the numerous Category 1 devices. The intent
of FHWA is not to simply transfer the keeping of an approval list for Category
1 devices to the highway agencies or to industry associations. The details
of a self - certification program are left to the highway agency discretion
but we would expect it to be commensurate with the risk to the traveling public.
A list of accepted devices is not a necessary part of a self-certification
program. A national association may keep a list of Category 1 devices as a
service to their members at their discretion. Other associations have created
similar programs for their members to reduce the burden and increase the confidence
of their member's customers. Often a mark or label is used to identify each
product as listed as certified by that association.
2.10 QUESTION - If a highway agency does not
believe that the vendor's self certification of a device is accurate, what can
ANSWER - By the nature of the Category 1 devices
we would expect this to be a rare occurrence. First, the highway agency should
review the basis (supporting information). Since the vendor's self- certification
is subject to approval by the individual highway agencies, if they find it
unsatisfactory they will discontinue accepting it. If the highway agency has
an actual or suspected product failure, they should perform tests or have
an independent or "check" test performed.
2.11 QUESTION - A contractor has devices in
his inventory that he believes meet Category 1 but is having problems obtaining
a letter of self-certification for them from the manufacturer. Does that mean
these devices cannot be used on the NHS after the October 1st date?
ANSWER - A vendor who is supplying the devices
for use on a highway agency's project is responsible for the self-certification.
Therefore the contractor can self-certify his current inventory of Category
1 devices as meeting NCHRP Report 350 standards if he is willing to be responsible
for the crashworthiness of the devices.
2.12 QUESTION What should be in the letter of
ANSWER - The letter should contain at a minimum:
A title, e.g., "Certificate of Crashworthiness";
Name and address of vendor making the certification.
Unique identification of the certificate (such as serial number) and of each page and the total number of pages;
(iv) Description and unambiguous identification of the item tested;
Identification of the basis for the self certification process used and to what Test Level of NCHRP Report 350. This basis as listed in the July 25, 1997-memo as crash test experience with similar devices or years of demonstrably safe operational performance. (Simplified crash testing showing that a device poses no risk to vehicle occupants may be used to support the manufacturer's certification. This simplified testing must, as a minimum, be documented by a written report, observed by an independent, impartial observer, recorded on videotape, and include a means, other than the test vehicle's speedometer, for determining the vehicle speed at time of impact.)
A signature and title, or an equivalent identification of the person(s) accepting responsibility for the content of the certificate (however produced), and date of issue;
A statement that the certificate shall not be reproduced except in full.
2.13 QUESTION - Can a Category 1 device be self-certified
by a vendor as safe solely on the basis of height and weight?
ANSWER - No. Category 1 devices will be allowed
based upon the vendor's self-certification if the device meets a specification
proved safe by crash or surrogate testing, crash testing, or safe operational
performance. The self-certification is based on an analysis and determination
by the vendor that the size, weight, material and shape are similar to devices
proven safe. We expect the vendors would have an analysis on file to support
2.14 QUESTION - Is there crash test information
available to assist vendors in analysis of their Category 1 device?
ANSWER - Acceptance letters of all work zone traffic
control devices are posted on the FHWA Office of Safety's webpage - http://safety.fhwa.dot.gov/roadway_dept/road_hardware/listing.cfm?code=workzone.
Crashtesting summaries are included in each letter of acceptance. A video
or videos will be available from the FHWA-NHTSA National Crash Analysis Center
for a fee. The center's homepage is http://gwuva.gwu.edu/ncac/.
2.15 QUESTION - Many traffic control contractors
manufacture their own Type III barricades. This will be costly; those costs
will be passed on to the State Departments of Transportation.
ANSWER- [We assume that the above comment means
that since many TCD contractors currently manufacture their own devices it
will be more costly for them to begin using crashworthy work traffic control
It may be marginally more costly to begin using a crashworthy
device rather than a noncrashworthy device. For example, if a TCD contractor
begins to manufacture a crash-tested generic design, the additional cost will
be that of revising the manufacturing process. If a TCD contractor decides
to have their own type III barricade design crash-tested the only cost is
that of the crash test(s). This of course will be amortized over the number
of barricades built.
There may be an increase in the effort spent in quality
control from the existing level so that a contractor can ensure that each
device is manufactured correctly.
A "generic" Type III barricade design was distributed
by FHWA in our acceptance letter WZ-54 dated September 15, 2000
2.16 QUESTION - There is a lack of uniformity
among work zone traffic control devices. What if the States use devices that
have not been found acceptable by the FHWA?
ANSWER - The provision in our July 25 memorandum
permits a State to use a "home grown" device it has determined to
be crashworthy according to the NCHRP Report 350. FHWA headquarters acceptance
is not a requirement.
If a device is determined to be crashworthy, it will be
the State's prerogative to accept or reject that product, as it has always
been. The FHWA will not take a position on State's selection from among competing
2.17 QUESTION - Will the implementation of the
NCHRP Report 350 procedures mean the banning of wooden barricades?
ANSWER - The NCHRP Report 350 procedures are not
material based, but performance based. Accordingly, the appurtenance design
is being evaluated and not solely the material. While we may speculate about
the potential crashworthiness of a class of appurtenance, crash testing and
in- service evaluation is the validation. Testing to date has found that a
variety of materials are acceptable for Type I and II barricades, but that
wood ought to be avoided for Type III barricades and other large structure.
2.18 QUESTION - How will all of the varieties
of barricades in current use be tested?
ANSWER - We look to the industry to recommend how highway
safety can best be served when crashworthy barricades are required. If a small
number of standard crashworthy barricade designs could be developed, the various
manufacturers would have an easier time providing crashworthy barricades.
The standard designs should provide guidance on variations in size, materials,
fastener hardware, permissible auxiliary devices, etc.
The results of a survey conducted by the American Traffic
Safety Services Association (ATSSA) will be most helpful in determining the
extent of the crash tests needed to qualify (or disqualify) the range of currently
used barricades. ATSSA intends to sort the barricades and other devices into
categories and the "worst case" example(s) from each Category tested
to qualify the remaining devices in a category.
2.19 QUESTION - Type III barricades need to be
strong enough to be easily relocated without breaking or coming apart.
ANSWER - We agree that Type III barricades must
withstand the rigors of movement at a construction site, but we also believe
that they can be designed so that they do not present an undue hazard to the
2.20 QUESTION - Manufacturing their own equipment
allows a contractor to control their own work. Will having crashworthy barricades
ANSWER - As long as satisfactory quality
control is used and the devices meet the requirements of NCHRP Report 350
, contractors and other entities can manufacture their own devices. For example,
there are generic Type III barricades mentioned in the Roadside Design Guide
of perforated square metal tubes, plastic tubular elements or wood that have
been satisfactorily crash tested and seem suitable for easy assembly.
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3.0 QUESTION (NEW)
- Can I substitute a Lexan or fiberglass sign panel for a polyethylene
or polypropylene corrugated plastic sign?
ANSWER - The corrugated
Lexan plastic substrate that is 16 mm (5/8 in) thick has been successfully
crash tested on certain portable sign stands [See WZ-52 dated September 21,
2000, and WZ-69 dated May 9]. However, the material properties of Lexan are
significantly different from the lightweight corrugated plastic substrates.
Therefore, Lexan is not interchangeable with other substrates. Fiberglass
substrates have not been crash tested and are not yet acceptable.
3.1 QUESTION: "Compact" sign stands (NEW) - Aren't all compact stands with roll-up signs crashworthy?
ANSWER - "Compact" sign stands are "X-Footprint" sign stands of steel or aluminum with a short mast. For the purposes of this Q&A, the mounting height of a 1220
mm x 1220 mm (48 x 48 in) diamond sign is 300 mm to 450 mm (12 to 18 in) only.
A number of manufacturers have crash tested compact sign stands. These stands
have performed well because there are no metal elements at a height that can
impact the windshield during a crash.
Based on the results of crash testing of these designs we have identified
elements that contribute to the successful crashworthy performance. Based
on a declaration of conformity and potential for crashworthiness, FHWA will
review requests for acceptance of compact sign stands conforming to the list
of conditions below. FHWA will decide whether to accept the stand or require
Requests must include:
- Complete drawings and specifications on the stands and roll-up signs (including welds and connecting hardware, and overall weight of sign stand)
- Information on any evaluations (e.g., informal crash testing) that may have been conducted.
- An engineering analysis of the crashworthiness of the stand. This analysis may be performed by the manufacturer or third party, such as a crash test laboratory.
- A declaration from the petitioner that they consider the device to be crashworthy.
The following conditions apply to FHWA's acceptance of these stands based
on the petitioner's declaration of conformity:
- Mounting height is between 300 mm to 460 mm (12 to 18 in) from the ground
to the bottom of the sign.
- Square tube legs and the short mast should be no larger than 32 mm (1-1/4
in) on a side.
- Maximum vertical mast of steel or aluminum is no taller than necessary
to grip the bottom of the vertical fiberglass brace. The mast may not extend
to the middle or top of the sign. The grip should be a quick-release type
that would allow the vertical fiberglass brace to pull out quickly, releasing
- Fiberglass bracing of the roll-up sign should be no wider than 32 mm
- The horizontal fiberglass brace should be no thicker than 4.76 mm (3/16
- The vertical fiberglass brace should be no thicker than 6.35 mm (1/4
- No flags or lights may be added.
Compact stands that have been successfully crash tested and found acceptable
by FHWA do not need to meet all of the above criteria.
3.2 QUESTION: Lightweight
substrates on permanent sign supports (NEW)
- Can the new, lightweight substrates that have been crash tested on work zone
portable sign stands be used on permanent breakaway sign supports?
ANSWER - The
following substrates may be used on permanent (ground-mounted) breakaway sign
supports, without further crash testing, as long as they are attached in such
a manner that they will not separate from the supports when impacted:
- Corrugated polypropelylene and polyethylene plastic substrates
- Aluminum faced composite laminates
- Corrugated Lexan plastic signs (e.g., Endurance)
This may be accomplished if a washer (approximately 25 mm or 1 in o.d.) is
used under the head of the bolt.
3.3 QUESTION(NEW)- Can we hide work zone signs with a plywood cover? Will
they still meet 350?
ANSWER - Covering signs in work zones when the work is
done for the day and the message is no longer needed is a common practice.
We have no policy prohibiting plywood covers as the basic breakaway criteria
for a ground mounted sign support, whether in a work zone or for a permanent
sign, is the vehicle's delta V during the impact. This criteria dates from
1985 and wasn't affected by Report 350. When we started talking about crashworthiness
of portable/temporary sign stands, delta V wasn't a problem since every portable
sign stand can be easily knocked aside without slowing the car much, even
if parts of it come loose and spear the occupants. So we decided that our
criteria would be "no holes in the windshield" for these stands
placed right on the pavement or immediately adjacent to it. This criteria
only applies to work zone Category 2 devices.
The implication here is that we are OK with a ground-mounted sign support
that penetrates the occupant compartment. That's not quite true, of course.
The worst performing sign support that anyone ever sent us was a perf square
steel tube support where the top of the sign hit the glass. The delta V in
this qualifying test was OK so we ruled it acceptable, but marginal because
of the windshield damage.
Now, back to the sign covers, which of course only apply to ground mounted
signs. FHWA is not in a position to prohibit plywood or aluminum covers yet
as we really don't have any hard evidence that they cause a problem. We might
imagine that in some hits the cover will come loose and hit the impacting
vehicle or fly into other traffic, but that's not enough to base a policy
on. Anyone with anecdotal evidence that this happens is asked to share it
FHWA will advocate a sign crashworthiness study that will look into sign
covers in particular, and also look into the question of base bending - yielding
supports in general, like the ground mounted Telespar and u-channel posts
that result in substantial windshield damage at some combinations of sign
height and vehicle height. We looked at this briefly when the MUTCD was being
re-written but need to delve further to develop a policy.
Back to the question of covering the sign with something safer. The typical
trash bag plastic is so thin that the sign is sometimes visible through it.
It can also traps moisture causing problems with the sheeting. There is one
company out there that makes "sign socks" which are woven plastic
covers - they are opaque but let air circulate. I have no doubt that these
flexible sign covers pose no additional hazard.
3.4 QUESTION: Interchangeability of Roll-Up Signs(NEW)
- If a portable sign stand has been crash-tested with roll-up
signs and accepted by FHWA, can I use any roll up sign on it?
ANSWER - All roll-up sign fabrics are acceptable on a crashworthy
sign stand that has been successfully tested with roll-up signs. However,
the fiberglass ribs must not be wider than 1 1/4 inches. The vertical rib
may be no thicker than 1/4 inches, and the horizontal rib may be no thicker
than 3/16 inches. If a vendor certifies that their fiberglass ribs conform
to these dimensions, then the sign may be used on any portable sign stand
that has been tested and accepted with roll-up signs. (There are crashworthy
roll-up signs with more substantial ribs, but their use is limited to the
stands that they were crash tested with.)
3.5 QUESTION - There are many varieties of trailer-mounted
sign supports. Will they have to be crash tested?
ANSWER - Yes. The crashworthiness of trailer-mounted
sign supports is a concern. We understand that some have been banned by certain
States because of the potential hazard. Two such trailers have been successfully
tested - those of Texas and Montana.
3.6 QUESTION - How will the sign substrate affect
the performance of a portable sign support? Plywood (now allowed) will perform
differently from aluminum.
ANSWER - In crash tests of various types of portable
sign systems, both the plywood and the aluminum substrates separated from
the sign support and penetrated the windshield. The fabric sign panel performed
satisfactorily when tested. Other substrates are currently being considered
Improvements in the connections between sign panels and
supports may address the problem of separation for some type of supports.
Also, the use of plastic sign substrates for use with plastic drums has been
successfully crash tested by the Texas Transportation Institute.
Rigid plastic substrates and aluminum/plastic "sandwich"
substrates have become very popular. We are currently (February 2001) working
with distributors of these materials to find similarities that will allow
us to accept substrates made by different manufacturers. However, it will
be more difficult to "cross the lines" and accept plastic substrates
based on tests of aluminum sandwich signs, for example.
3.7 QUESTION - Should portable / temporary sign
stands be crash tested at a 90 degrees angle as well as head on?
ANSWER - NCHRP Report 350, in section A3.2.3,
"Because errant vehicles may approach a support structure,
work zone traffic control device, ... at various angles, it is recommended
that the device be tested assuming the most severe direction of vehicle approach
consistent with the expected traffic conditions..."
Temporary sign stands are often used near intersections
where traffic approaches from many directions. Also, when along highways sign
stands are sometimes turned 90 degrees to conceal the message from the driver.
In this orientation the cross brace that spreads the fabric sign panel is
critical. Full-scale testing has shown that tubular metal cross braces will
penetrate the windshield, whereas thin, flexible cress braces will not. Therefore
any portable or temporary sign stand should be evaluated to determine if the
cross brace is a potential hazard.
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4.0 QUESTION - Concerning temporary concrete barrier--we (State DOT) don't want to get rid of what we have and use something new in 1998 that will meet Report 230; then in 2002 get rid of that, and use something that will meet NCHRP Report 350. We want time to find something acceptable to use that will meet 350. A phase-in period is desired. The life of a barrier could be ten years or more.
ANSWER - We agree it seems reasonable to begin
using portable concrete barrier(PCB) joint details that meet the requirements
of NCHRP Report 350. There are several currently available for use. As of
January 1, 2001 these include the Iowa PCB (TL-3, F- shape w/pin & loop),
Rockingham Precast (TL-3, F - shape w/ slotted tube/T -bar connection), JJ-Hooks
(NJ and F-Shapes), Idaho and Virginia (20-ft long NJ and F- shapes, respectively,
w/pin and loop connections), and the Low Profile barrier (TL-2). Other concrete
shapes and some water-filled plastic barriers have also met Report 350 test
The AASHTO / FHWA agreement permits the use of connections
meeting NCHRP 230 guidelines until they complete their normal service life.
Connections that do not meet those criteria may be considered for a retrofit.
In addition in the current work zone pooled funded study it has been proposed
to develop a retrofit for strengthening existing PCB joint details. If successful
that may allow continued use of some non-conforming PCB connections on the
NHS until the end of their useful service life.
4.1 QUESTION -Will contractors be allowed to
continue using their existing barriers (providing it is one of the five barriers
identified tested in the 1996 RDG) until a reasonable amount of time has passed
after the NCHRP Report 350 acceptance of a non-proprietary, reasonably priced
ANSWER - All existing barrier designs can be used
until October 1, 2000, as long as they are still serviceable and conform to
the NJ or F shape. After October 1, 2000, they must be one of the five Report
230 designs listed in the “crash tested and operational” section of Chapter
nine of the 1996 RDG (or otherwise meet the tensile and moment requirements
of the AASHTO / FHWA agreement) or a design that has met Report 350 test requirements.
Barriers that meet the connection requirements but have not been tested under
Report 350 may be used throughout their service life unless a transportation
agency sets a specific phase out period.
No new non-NCHRP Report 350 barriers should be purchased
or manufactured for use on projects advertised for bids after October 1, 2002.
4.2 QUESTION - Large deflection of portable barriers
in the adjacent work space is a concern.
ANSWER - Agree, that is why maximum allowable deflection
should be considered when selecting the type of barrier to use. When using
PCB's, the maximum allowable deflection should govern whether to use stiffeners
for joints or attachment of the barrier to the pavement or deck.
4.3 QUESTION - The 25-degree angle hit is questionable
in real applications.
QUESTION - Installing a device exactly is often
not practical in a real application as it was tested (installing barriers on
a curve, for example).
ANSWER - An appropriate answer to this is to quote
from NCHRP Report 350, "Recommended Procedures for the Safety Performance
Evaluation of Highway Features."
From the Summary:
"These procedures are devised to subject roadside
safety features to severe vehicle impact conditions rather than to typical
or average highway situations. Although the innumerable highway-site and safety-feature
application conditions that exist are recognized, it is impractical or impossible
to duplicate these in limited number of standardized tests. Hence, the approach
has been to normalize test conditions: straight longitudinal barriers are
tested although curved installations exist; flat grade is recommended even
though installations are sometimes situated on sloped shoulders and behind
curbs; idealized soils are specified although roadside safety hardware are
often founded in poor soil or frozen ground. These normalized test conditions
have a significant effect on a feature's performance but are of secondary
importance when comparing results or two or more systems.
Page 4, Section 1.4 PERFORMANCE LIMITATIONS, 2nd paragraph:
"For these reasons, safety features are generally
developed and tested for selected idealized situations that are intended to
encompass a large majority, but not all of the possible in-service collisions.
Even so, it is essential that test results be evaluated and interpreted by
competent researchers and that the evaluations be guided by sound engineering
Note: The Test Levels 1 through 3 in NCHRP Report 350
represent increasing severe impact severities. In general, each impact severities
is described by a combination of test vehicle( weight), impact speed and impact
angle. The decision in NCHRP Report 350 to vary impact severities by holding
the vehicle and angle constant while varying the speed was based on the desire
to limit the cost of testing rather than an attempt to mimic real life conditions.
Therefore, depending upon the site conditions a portable concrete barrier
meeting TL-2 test criteria may be appropriate.
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5. CRASH CUSHIONS AND TRUCK MOUNTED ATTENUATORS
5.0 QUESTION - Please clarify the FHWA position on the use of NCHRP Report 230 qualified work zone crash cushions after October 1, 1998.
ANSWER - FHWA is no longer reviewing testing conducted
under NCHRP Report 230 guidelines, so there will be no new crashworthy work
zone crash cushions found acceptable that do not meet the NCHRP Report 350
guidelines. The AASHTO / FHWA agreement calls for new units purchased after
October 1, 1998, to meet Report 350 guidelines. Existing TMAs and Work Zone
crash cushions may be used until they complete their normal service life.
5.1 QUESTION - Since existing NCHRP Report 230
TMA's have been tested at the equivalent of Test Level 2 will they still be
allowed after October 1, 1998.
ANSWER - The Test Level 2 is the basic test level
for TMA's in NCHRP Report 350. As such, TMA's designed to this test level
can be used on the NHS. Review of crash performance shows that TMA's designed
to this test level perform well. A transportation agency may use TMA's designed
to test level 3 if they want the higher performance.
5.2 QUESTION - If a State wants to use vehicles
with truck mounted attenuators in maintenance activities or in force account
work on the NHS, does FHWA expect these State-owned TMAs to be upgraded to NCHRP
Report 350 (or modified 350) criteria? Are existing non-NCHRP Report 350 TMAs
not going to be allowed even if they are in good shape?
ANSWER - Existing NCHRP Report 230 TMAs can be
used on the NHS until the end of their useful life (see question 5.3 below).
Any new TMA's purchased should meet NCHRP Report 350 criteria.
5.3 QUESTION - What is the date that TMA's used
on projects on NHS highways have to conform to NCHRP Report 350? If Oct. 1,
2002, is correct, do TMA's fit under Category 3? If they do not fit under Category
3, then what category do they fit under?
ANSWER - For the purpose of implementing the crashworthiness
of WZ devices, TMAs may be considered as Work Zone Crash Cushions. They are
Category 3 devices that come under the October 1, 1998, limit. Our intention
is that TMAs (and other work zone attenuators) meeting Report 230 guidelines
may continue to be used until they are worn out and ready for replacement
with hardware conforming to NCHRP Report 350.
5.4 QUESTION - NCHRP Report 350 indicates in
Section 126.96.36.199 on page 12 that it may be possible to extrapolate results of
a TMA test for supporting vehicles of differing masses. It goes on to indicate
that at the time of that writing no known validated procedures exist to make
such extrapolations. Our question is, if a TMA manufacturer has a lesser weight
recommended for the support vehicle than what they were tested at and they have
based this weight off of some procedure, are they required to submit this to
the FHWA for approval? It is our understanding that one company already has
a lesser weight that can be used, but they did not have to have the approval
of the FHWA.
ANSWER - Our procedures permits the use of devices
/ procedures that have been shown to meet NCHRP Report 350 guidelines without
FHWA Headquarters acceptance. Our acceptance letters are a service to the
industry that acknowledge the crashworthiness of a device so that a manufacturer
does not have to provide the same detailed documentation to every highway
agency. If a highway agency considers itself qualified to review the vendor's
documentation in light of NCHRP Report 350, they are free to do so, preferably
with the concurrence of the FHWA division office when NHS routes are concerned.
To your point of the lesser-weight host truck, Report 350 recommends a support
vehicle weight of approximately 9000 kg. Virtually all TMA testing is done
with a vehicle of this weight. There is no acceptable procedure to extrapolate
TMA performance with heavier or lighter support vehicles. Report 350 recommends
testing with a support vehicle similar to one which will be used in service.
Our acceptance letters usually indicate that the test host vehicle is the
maximum mass vehicle we consider acceptable with the covered TMA and, if not
stated, is implied. If a contractor chooses to use a lighter vehicle to mount
the TMA, then the contractor is responsible for following the TMA manufacturers
recommendations and for being aware of the effect that a lighter vehicle will
have on the roll-ahead distance and on the driver of the shadow vehicle. NCHRP
Report 350 includes evaluation criteria for the support vehicle as well as
the impacting vehicle for TMA tests.
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6.0 QUESTION - How were work zones devices determined to be in category IV?
ANSWER - Category IV devices are devices which have proven to have
significant value in the work zone by contributing to safer traffic operation
though these devices may cause great harm to occupants of impacting vehicles.
We believe that, as currently configured and deployed, these devices provide
a net benefit to motorists. Substantial crash experience to date shows that
crashes with these devices are rare. They have been identified by FHWA as
portable, usually trailer-mounted, devices such as area lighting supports,
flashing arrow panels, temporary traffic signals, and changeable message signs
which are often used in or adjacent to the traveled way. The AASHTO / FHWA
agreement calls for these devices to be studied and an implementation date
announced by October 1, 2000.
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We would not expect to identify any new category IV devices unless they have a proven substantial operational benefit.
For further questions please contact:
If you have questions that concern implementation within a specific State, please contact that respective Division Office.