U.S. Department 

Of Transportation 

Federal Highway 

Administration

400 Seventh St., S.W. 

Washington, D.C. 20590 

June 15, 1987 

Refer to: HNG-14/SS-05 

Regional Federal Highway Administrators 

Direct Federal program Administrator 

By notice of proposed rulemaking (NPRM) published November 11, 1986, the FHWA proposed to adopt 

for application on Federal-aid highway projects the AASHTO’s revised “Standard Specification for 

Highway Signs, Luminaires and Traffic Signals, 1985.” The comment period on the NPRM closed on May 

11. 

It is expected that a final rule will be issued to adopt all of the 1985 AASHTO specification except for 

Section 7, Breakaway Supports. Any decisions on Section 7 will be delayed until completion and analysis 

of the on-going crash testing program of existing luminaire hardware at FHWA’s Federal Outdoor Impact 

Laboratory (FOIL). When done, the results will be published in the Federal Register and additional time 

will be provided for public comment. A final rule on Section 7 would not be issued until after that time. 

In the interim, FHWA’s requirements for breakaway sign and luminaire supports on Federal-aid projects 

will remain to be those found in Section 7 of the previously FHWA adopted 1975 AASHTO Specification 

for Sign and Luminaire Supports. However, a State has the option to begin applying on Federal-aid 

highway projects the more stringent 1985 AASHTO specification if it so chooses. 

The FHWA’s capability testing of several luminaire support systems should be completed by mid-1987. 

However, several significant additions/modifications to the FOIL testing facilities are necessary before we 

will be in a position to begin testing direct-burial sign supports or multiple breakaway sign supports for 

larger signs. We are now investigating possible additions/modifications to the testing facility and are 

hopeful they will be implemented in about a year. 

In the meantime, we have received several inquiries seeking information on sign support systems which 

may have already been tested in accordance with the 1985 AASHTO specification. Bases on a review of 

our files and other information provided to us, we have assembled the attached listing of sign support 

systems which have been crash tested with an 1,800-pound vehicle and have satisfied the breakaway 

requirements of the 1985 AASHTO specification. 

When using the attached listing, careful attention should be paid to the descriptions of the tested systems 

and the soil conditions used. Demonstration of satisfactory breakaway performance is limited to the system 

tested and soil conditions noted. We have encouraged testing several of the sign support systems in both 

strong (S-1) and weak (S-2) soils as defined in NCHRP 230. 

However, in many cases the support was tested in only the strong soil. When this occurs, the crash test 

then only demonstrates satisfactory breakaway performance if the support is placed in a strong soil. 

The attached listing is not intended to be all inclusive. If you are aware of additional sign support systems 

that have been tested by a State or others in accordance with the new AASHTO requirements, we would 

appreciate being advised of the test results. As additional information is provided to us, we anticipate that 

the attached listing will be updated. 
For sign support systems of comparable design to ones for which crash test data are available (as shown on 

the attached listing) and having support post sizes and/or weight equal to or less than the crash tested 

system, it is our opinion that these sign support systems can be accepted as having satisfied the breakaway 

requirements of the 1985 AASHTO specification subject to the same limitations as the crash tested system. 

Additional information you have available or questions you have on this subject should be directed to Jim 

Overton (FTS 366-1331) of my staff. 

 Sincerely yours, 

 L. A. Staron, Chief 

 Federal-Aid and Design Division 

Attachment 
Sign Support Systems 

Compliance with 1985 AASHTO Specification 

June 1987 

The following listing covers sign support systems which have been crash tested and meet the breakaway performance requirements of tSpecifications for Highway Signs, Luminaires and Traffic Signals, 1985.” The listing is based on information available to Federal High(FHWA) Office of Engineering as of the date assembled and is not intended to be all inclusive. Updates are planned as additional inforavailable. When using this listing careful attention should be paid to the description of the tested system and the soil conditions used. Demonstratperformance is limited to the system tested for the soil conditions noted. The FHWA does not endorse any specific product or system listed herein. Rather this listing is presented for informational purposes to tested in accordance with the test parameters in the new 1985 AASHTO specification. Sign Support System Test Test Car 

Weight 

Impact 

Speed (mph) 

Change in 

Velocity (fps) 

Stub 

Height 

Comments 

1. Perforated Square Steel Tube (single support) 

TTI 7024-3 (5/85 – Ariz. DOT 

1770# 20.0 3.5 OK Tested in strong so

(See attached Ariz. DOT Dr. 4-s-4.16 – Fig. 1) 

TTI 7024-4 (5/85 – Ariz. DOT 

1770# 56.8 8.5 OK Reference: Ariz. D

HPR-RL-1 (31). 

2. Single 3 lb. High Carbon Billet Steel U-Post. 

TTUI 7024-8 (11/84 0 Ariz. DOT 

1800# 19.9 6.0 OK Tested in strong so

Reference: Same a

(See attached Figure 2) TTI 7024-7 

(11/84 – Ariz. DOT 

1800# 60.5 3.1 OK 

Also see Note No. 

3. Dual 3 lb. High Carbon Bilet Steel U-Post. 3’-7’ post spacing – both posts hit 

TTI 7024-22 9/85 – Ariz. 

1833# 20.0 9.4 OK Tested in strong so

Reference: Same a
DOT 

(See attached Figure 3) TTI 7024-

23 (9/85 – Ariz. DOT) 

1833# 62.8 11.7 OK 

Also see Note No. 

4. Arizona Dual Legged Slip Base S4x7.7 (hinge at midheight of panel). One post hit. 

TTI 7024-1 (11/84 – Ariz. DOT) 

1820# 19.6 5.0 - - - Reference: Same a

(See attached Ariz. DOT DR. 4-s4.01 & 4-s-4.05 as modified – Fig. 4 & 4A) 

TTI 7024-2 (11/84 – Ariz. DOT 

1820# 59.3 3.0 - - - Also see Note No. 

5. Dual Legged Slip Base – 12WF45 12’ x 24’ sign panel 

ENSCO 1147-1010 (6/79) 

1617# 20.6 9.9 

(See Note 

No. 3) 

- - - Reference Rept No

One Post hit. (See attached Figure 5) 

ENSCO 1147-1009 (6/79) 

1516# 61.0 8.8 - - - Utilized Texas Typ

Bolts tightened to plate at the joint. (

6. Minute Man breakaway device for use with steel flanged channel sign supports 

Reference Mr. Staron’s 1/29/87 letter to Minute Man Anchors, Inc. 

7. QWIK-PUNCH tube system Reference Mr. Staron’s 10/3/86 letter to Allied Tube and Conduit Corp. 8. MICRO=LAM laminated veneer lumber breakaway sign post 

Reference Mr. Staron’s 8/19/96 letter to Trus Joist Corp. 

9. POZ-LOC anchor system Reference Mr. Van Ness 7/14/86 and 5/13/86 letters to Southwestern Pipe, Inc. 

Note No. 1 – The tested U-post supports included splices with the upper lap going approximately 5 feet above ground. The spliced sup

satisfactorily in these tests. However, we are concerned that environmental effects over time could cause the fasteners in the splice to w

to open under impact. Because of this we have recommended that a splice should not extend more than 24 inches above the ground and of the splice should be in front of the upper post. Note No. 2 – The tested dual legged support system included inclined slip bases. For multiple legged supports with hinges, we have su

slip bases. 
Note No. 3 – Performance of this system during the 20 mph test was considered marginal as the hinge failed to activate and the entire s

on top of the vehicle, causing deformation on the roof. The 20-foot long support leg weighed approximately 800 lbs. We would suggeweight of a support leg to be used in these circumstances and recommend use of lesser weights to improve performance. Note No. 4 – The current recommended torque values for slip base bolt sizes are: Post Size 

(lb./ft) 

Slip Base Bolt 

Diameter 

(inches) 

Suggested Clamping 

Force 

(lb.) 

Slip Base Torque 

(lb. –in.) 

0.8 1⁄2 920-1380 95-142 

9-20 5/8 1740-2660 226-345 

21-30 3⁄4 2400-3600 369-554 

30+ 1 2400-3600 490-735 

For fuse plate connections we recommend use of standard high strength bolting practices. The fuse plate connection should be designe

anticipated wind load. 

Further information on the above listed items is attached. 



Arizona Dual Legged Slip Base 

Details of the tested system are shown in Figures 4 and 4A (see following two sheets) with 

exceptions noted below. 

An 8-foot wide by 5-foot high extruded aluminum panel was mounted on the two S4 x 7.7 

posts, with the lower edge of the panel approximately 7 feet above ground. Attachment was 

with six post clamps and lock nuts per post, all of which were above the hinge. The posts were 

spaced 5 feet apart. 

It is noted that the hinge was placed at the midpoint of the panel as sown on Figure 4, not as 

shown on Figure 4A. It is also noted that the hinge details differed from those shown on 

Figure 4A. For the installation tested, the signpost was not cut completely in two as shown. 

Instead, the flange adjacent to the sign panel and the web was cut but the back flange was not 

cut. The “friction fuse plate” was installed as shown but there was no need for the “back 

plate”. 


Dual Legged Slip Base 

(Texas Type Design) 

The general features of the system tested are shown in Figure 5 (following). 

The sign blank was 12 ft. high by 24 ft. wide, made from 5/8 in. plywood. The blank had 4 

aluminum windbeams, the top one being 3Z2.33 and the others being special T-beam. The top 

windbeam was fastened to each leg with two 1⁄2 in. diameter bolts. The T-beams were fastened 

to the leg with cast aluminum clips and 3/8 in. diameter aluminum bolts. The distance from the 

bottom of the sign to the ground was 8.5 ft. 

The legs were fabricated from 12WF45 steel beam. They were spaced at a 15 ft. span and 

incorporated a Texas type slip base. One-inch diameter slip base bolts tightened to 5,000 lb 

were used. 

The legs included an upper hinge design where the support leg was cut clean though and a back 

hinge plate and a slotted front hinge plate were used. The front hinge plate was secured with 3⁄4 

in. diameter bolts tightened to 28,000 lb.