Effective Shoulder Width on Rural Highway System Related to Roadway Departure Crashes

Details

• Creators:
  Barahona, Mario ; Bandaru, Vamsi Krishna ; Romero, Mario ; Tarko, Andrew
• Corporate Creators:
  Purdue University. Joint Transportation Research Program
• Corporate Contributors:
  Indiana Department of Transportation ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  Countermeasures Crash Modification Factors Highway Safety Ran Off Road Crashes Road Shoulders Rumble Strips Rural Highways Safety Safety Counter Measure Shoulder Width Two Lane Highways

  More +
• Publication/ Report Number:
  FHWA/IN/JTRP-2025/38
• DOI:
  https://doi.org/10.5703/1288284318601
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Indiana
• Edition:
  Final Report
• Corporate Publisher:
  Purdue University. Joint Transportation Research Program
• Abstract:
  Roadway design plays a crucial role in traffic safety, particularly on rural roads. This research investigates the safety effectiveness of shoulder width on Indiana’s rural two-lane highways, and to use this understanding to provide a basis for more effective shoulder improvement programs. Although previous studies have established the benefits of shoulder widening in other states, limited research has been conducted in Indiana conditions. This research aims to evaluate the safety effectiveness of shoulders on rural roads in Indiana and to propose a practical and systemic approach to identifying road segments that require additional attention and possible need for shoulder improvements. A negative binomial model with random effects was implemented to evaluate run off road crash frequency on two lane rural roads in relation to shoulder width. Nine years of crash data from 2015 to 2023 from more than 5,000 miles of Indiana rural highways was used. This model incorporates geometric factors including shoulder width, traffic exposure, and the presence of rumble strips to quantify the impact of shoulder width on crash frequency. Crash Modification Factors (CMFs) were developed based on the existing combinations of shoulder and lane width, and proposed design alternatives. This allows for a comparison among different configurations. Findings indicated that increasing shoulder width generally reduces crash frequency. Installing a 5- or 6-ft shoulder in a location that previously did not have a shoulder resulted in the highest reduction in crashes according to CMFs. Shoulders equal to or exceeding 7 ft showed diminishing safety benefits when compared to shoulders of 5–6 ft. This is potentially due to the additional risk-taking by drivers under seemingly safer conditions. The presence of roadside rumble strips was found to reduce run-off-road (ROR) crashes by 9.1%.
• Format:
  PDF
• Funding:
  SPR-4853
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:363b5b5840368b4e88653114aace5d42b3ea1e0eb1be6c46f6531daf40dbeb630e0360f6c79105c79d8f702c925842f0c2ff56b4986c0f14e4b3ba6ff707bddf
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/91192/dot_91192_DS1.pdf
• File Type:
  [PDF - 6.70 MB ]