The expanding system of limited access, multilane highway facilities in the United States has enhanced traffic service between many varied origins and destinations. As a result, these facilities have not only reduced travel times and travel costs, but have generated additional travel by virtue of their technological splendor. The increasing dominance of multilane highways in terms of percentage of total vehicle miles travelled has produced a revolution in highway engineering philosophy. Higher design speeds, increased lane widths, lateral separation of opposing traffic streams, absence of passing restrictions, and increased traffic capacities were attributes intuitively sought. An ironic result is the emergence of new accident styles on roadways which had as their specific purpose the reduction of accidents. Dominant among these new styles was the "single vehicle ran off the road" type.

Recent investigations have shown that this accident mode may be the largest single contributor to fatalities on limited access, multilane facilities. Contributing to the preponderance of this accident type are some seemingly minor but potentially deadly elements of the roadway. Previous studies have been concerned with bridge piers located in the median, the location of median crossovers, and the horizontal and vertical dimensions of medians themselves. Problems have been created by rigidly fixed objects such as bridge walls or massive sign standard bases located in the gore area of bifurcating roadways and exit ramps.

Report Date


Report Number

No. 308

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The opinions, findings, and conclusions in this report are not necessarily those of the Department of Highways or the Federal Highway Administration.