South Dakota Department of Transportation
Project Synopsis
SD1993-04

Title: Crash Testing of Undrilled 4" X 6" Cedar Posts
Project Researcher: Christopher Brown,
Project Manager: Jon Becker
Research Period: 1/1/1900 - 1/1/1900
Status: Completed
Cost: $0.00

Problem Statement:Until a failing crash test was conducted on an undrilled 4" X 6" Southern Pine sign post as part of the Pooled Fund Study HPR-2(144), undrilled 4" X 6"s had been widely accepted for breakaway applications by many states, including South Dakota. As a result of this test, 4" X 6" timber posts were required to have 12" diameter holes drilled in them near the base to be accepted as breakaway. SDDOT began drilling the posts as required, but experienced some failures in cedar posts under normal wind loads not seen prior to drilling. Since cedar is the timber post material desired by SDDOT due to its weathering characteristics, availability and relatively low cost, and because it is of less strength than the southern pine originally tested, it was felt that it would be worth testing the undrilled 4" X 6" cedar post.

Findings:

Research Objectives:
1  To determine whether undrilled 4" X 6" cedar posts may be used in breakaway applications.
2  If necessary, determine what minimum modifications must be made to use 4" X 6" cedar posts in breakaway applications.

Research Tasks:
1  Perform crash test with an 1800lb vehicle travelling at 20mph impacting a 4' x 6' western red cedar sign post embedded in weak soil, mounting the sign blank so the top is a minimum of 9 feet high, using a sign blank size of 4'- 6" wide and 4' high, and burying the post at a depth of 4' minimum. Test procedures shall be in accordance with NCHRP Report 230, and acceptance criteria shall be that found in section 7 of the AASHTO Standard Specifications for Highway Signs, Luminaires and Traffic Signals. After test is completed, notify panel verbally and provide a brief written test report. If test passes, go to task three.
2  If test in task one fails, contact research panel and run the 20mph test in weak soil using the panel's specifications. If test passes, go to task three. If test fails, stop testing and go to task six.
3  Perform crash test at 60mph in weak soil, using the above parameters. If this test fails, stop testing and go to task six. If test passes, SDDOT will send the results from these tests to the FHWA. If FHWA accepts the test results, then testing will stop and task six will be performed. If FHWA determines more testing is required, tasks four and five must be accomplished.
4  Perform crash test at 20mph in strong soil, using the above parameters. If this test fails, go to task six. If test passes, perform task five.
5  Perform crash test at 60mph in strong soil, using the above parameters. If this test passes or fails, go to task six.
6  Prepare and submit final report and executive summary including test methods, data, findings, analysis, recommendations and any other pertinent information necessary to approve or reject design. Also provide a video tape documenting the crash testing.

Documents Available: