This study was conducted to summarize the known relationships between accident experience and cross-sectional roadway elements, along with accident reductions expected because of related roadway safety improvements. Such elements include lane width, shoulder width, shoulder type, roadside features, bridge width, median design, and others. A detailed review of literature and available safety research revealed that accident types related to cross-sectional elements on two-lane roads include run-off-road (including fixed-object and rollovers), head-on, opposite direction sideswipe, and same direction sideswipe. Lane widening can reduce these related crashes by up to 40%, whereas shoulder widening can reduce related accidents by up to 49% [for the addition of 8-ft (2.4-m) paved shoulders]. Improving roadsides can also contribute to the reduction of as much as 44% [for a 20-ft (6.1-m) increase in clear zone], whereas sideslope flattening can reduce single vehicle crashes up to 27% (for flattening a 2:1 sideslope to 7:1 or flatter). Bridge widening can reduce total bridge crashes by as much as 80%, depending on the width before and after widening. On multilane roads, wider and flatter medians are associated with a reduced rate of total crashes. Lower-cost multilane design alternatives found to reduce crashes compared to two-lane roadways include two-way left-turn lanes, passing lanes, and turnout lanes. Suburban and rural multilane designs found to significantly reduce crashes compared to two-lane roads include those roads having two-way left-turn lanes with three or more total lanes.


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 29-36
  • Monograph Title: Safety effects of roadway design decisions
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00715638
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Jan 23 1996 12:00AM