1 

TECHBRIEF: BRIDGE CURB/RAILING AND APPROACH TREATMENT FOR 

EXTREMELY LOW-VOLUME ROADS 

BACKGROUND 

Bridges cross over a variety of features ranging from drainage ditches to deep valleys and serve a 

variety of functions. There are several competing considerations when evaluating bridge railings: 

the risk of injury and death for vehicle drivers and occupants, the structural integrity of the 

bridge itself, and the service provided to the principal users of the bridge. 

The United States Bureau of Reclamation (USBR) is a Federal Land Management Agency 

(FLMA) responsible for 315 bridges within the National Bridge Inventory (NBI). The USBR 

inventory is dominated by low-speed and low-volume bridges. The Federal Lands Transportation 

Program (FLTP) was established in 23 U.S.C. 203 to improve the transportation infrastructure 

owned and maintained by FLMAs. 

There has been interest for several decades in developing selection guidance for the multiple 

performance, service, or test levels of bridge rails. The recent completion of the National 

Cooperative Highway Research Program (NCHRP) 22-12(03) (Recommended Guidelines for the 

Selection of Test Levels 2 through 5 Bridge Rails) provided this guidance, but did not address 

extremely low-volume roads nor low-speed roads.(1) FHWA, in collaboration with USBR, 

conducted a study to address this gap and create a guide for bridge rails and approach treatments 

for extremely low-volume, and low-speed roads. This tech brief summarizes the research and 

information used to develop the Guide for Bridge Curb/Rail and Approach Treatment for 

Extremely Low Volume Roads (the Guide).(2) The project also produced a research report that 

documents the entire effort: Bridge Curb/Railing and Approach Treatment for Extremely Low 

Volume Roads.

(3) 

EVALUATION OF EXISTING HARDWARE 

The research team compiled existing guidance for bridge rail design on low-and very lowvolume roads. There is variety in how States address bridge rail and approach treatments on lowvolume roads. (See references 2 through 10). Guidance for extremely low volumes (i.e., less than 

50 vpd) and low-speed roads is limited. One observation that is repeated throughout the literature 

review is that upgrading bridge rails on bridges servicing low-volume roads is generally not costbeneficial. Conversely, however, there are crash risks associated with these bridges that must be 

balanced with the costs of improvements to these bridges. 

NEW HARDWARE DEVELOPED 

The research team modified the MASH TL-1 low profile WVBR for installation on a lower 

strength bridge structure (e.g., 4x12 wood plank bridge deck), and assessed the crash 

performance under MASH TL-1 conditions using finite element analysis (FEA).(11) The research 

team then developed three alternative mount designs that met performance criteria in MASH for 
2 

TL-1 impact conditions and successfully contained and redirected the pickup with minimal 

damage to the system.

The research team also performed supplemental evaluations to determine the performance 

threshold for a 12-inch-tall timber railing regarding successful containment and redirection of a 

5,000-lb pickup. Although these lower profile railings do not meet MASH TL-1, a Technical 

Advisory Committee expressed interest in the limits for impact conditions at which these lowprofile barriers will successfully contain and redirect the 2200P vehicle (i.e., 5,000-lb quad-cab 

pickup). The only safety metric of concern was the tendency for the vehicle to override the 

barrier, which may be useful for bridge owners in assessing “risk” for bridge design options 

(e.g., to widen bridge or not) for these low-profile railing/curbs which are used on many narrow, 

single-lane bridges to support farming and logging industry. 

CONCLUSION 

The research team concluded that the 12-inch-tall curb/railing would successfully contain and 

redirect the 5,000-lb pickup at impact speeds of 20 mph when the impact angle was equal to 15 

degrees. The research team analyzed various combinations of angles and impact speeds and

concluded that impact severity does not appear to correlate well with the pass/fail conditions for 

the low-profile barrier. Success or failure was predominately determined by the tendency for the 

tire to climb the barrier during impact, which occurred more prevalently at impact angles greater 

than 15 degrees due to the tire tread having more contact with the railing.

The research team used the research results to develop the Guide for Bridge Curb/Rail and 

Approach Treatment for Extremely Low Volume Roads (Guide).(2) The Guide leads inspectors 

and engineers to practical, low-cost solutions based on the characteristics of the bridge, 

anticipated traffic, and the intended use of the bridge. The Guide also assists in determining if the 

existing bridge rails, associated roadside hardware, and other conditions can be left as-is; if 

improvements should be considered to achieve the safety performance goal; and, potential 

solutions that might be implemented to achieve the safety performance goal. 

The Guide follows inspectors and engineers with a two-part decision matrix. First, inspector and 

engineers inspect and evaluate the existing conditions at the bridge site and second, consider 

possible improvements to the bridge rails and approach hardware. The Guide also provides 

specific guidance for a variety of bridge rail mounting configurations, a form to characterize 

terminals and/or transitions, and worksheets to document bridge deck features, roadway features, 

and the presence of delineation. 
3 

REFERENCES

1. Ray, M., et al., Developing Selection Tables for Bridge Railing. 2013: researchgate.net. 

2. Carrigan, C. and Plaxico, C. (2022). Bridge Curb/Railing and Approach Treatment for 

Extremely Low-Volume Roads: Final Report, Report No. FHWA-FLH-23-003b, Federal 

Highway Administration, Washington, DC. 

3. Carrigan, C. and Plaxico, C. (2022). Guide for Bridge Curb/Rail and Approach Treatment for 

Extremely Low Volume Roads. Guide No. FHWA-FLH-23-003a, Federal Highway 

Administration, Washington, DC. 

4. IDOT, Bureau of Local Roads and Streets Manual, in Chapter 35, Roadside Safety. 2007. 

5. IowaDOT. Instructional Memorandum 3.213 Traffic Barriers (Guardrail and Bridge Rail). 

2013 07/18/2013 [cited 2020 09/21/2020]; Available from: 

https://iowadot.gov/local_systems/publications/im/rev_2013-02.pdf 

6. IowaDOT. Instructional Memorandum 3.230 Traffic Barriers (Guardrail and Bridge Barrier 

Rail). 2018 04/24/2018 [cited 2020 09/21/2020]; Available from: 

https://www.iowadot.gov/local_systems/publications/im/3230.pdf 

7. Seitz, R.J., et al., Guardrail and Bridge Rail Recommendations for Very Low-Volume Local 

Roads in Kansas. 2014. p. 166. 

8. Seitz, R.J., T. Salfrank, and T. Kansas Department of, Guardrail and Bridge Rail 

Recommendations for Very Low-Volume Local Roads in Kansas: Addendum to Include 

Bridges Up to 100 Feet Long and Traffic Volume Up to 100 Vehicles Per Day. 2017. p. 158. 

9. MoDOT and E.P.G. contributors. 606.1 Guardrail. 2019 07/22/2019; Available from: 

https://epg.modot.org/index.php?title=606.1_Guardrail&oldid=45956. 

10. SDDOT, Local Roads Plan. 2011. 

11. AASHTO, Manual for Assessing Safety Hardware. 2016, American Association of State 

Highway and Transportation Officials: Washington, D.C. p. 259.
4 

Researchers—VHB, in collaboration with RoadSafe, performed this study under contract 

693JJ320F000318. Christine Carrigan and Chuck Plaxico were the lead researchers; Catherine 

Chestnutt was VHB’s project manager and the project’s communications lead. The Contracting 

Officer’s Representative and Task Manager was Yanira Rivera of the FHWA Office of Safety 

Research and Development. 

Distribution—This TechBrief is being distributed according to a standard distribution. Direct

distribution is being made to the FHWA divisions and Resource Center.

Availability—This TechBrief may be obtained from the FHWA Product Distribution Center by 

email to report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at 

https://highways.dot.gov/research. 

Key Words—low-volume roads, bridge rail, approach treatments. 

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation (USDOT) in the interest of information exchange. The U.S. Government assumes 

no liability for the use of the information contained in this document. The U.S. Government does 

not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this 

TechBrief only because they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides highquality information to serve the Government, industry, and public in a manner that promotes 

public understanding. Standards and policies are used to ensure and maximize the quality, 

objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues 

and adjusts its programs and processes to ensure continuous quality improvement.