940.11 Three-Lane Cross-Sections

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Three-lane cross-sections (two through lanes with a TWLTL in the center) are approximately 25 percent safer than an undivided four-lane road and can provide comparable capacity provided that intersections are well designed. They work best in situations where traffic volumes are moderate and where the proportion of vehicles turning left is high. Discourage the use of TWLTLs in rural areas as their use in high speed, low volume situations can increase head-on crashes. Also, avoid them in urban areas where the design year traffic is expected to grow beyond 17,500 AADT. TWLTLs are best used with low to moderate driveway density (e.g., below 24 commercial driveways per mile equating to a spacing of about 440 ft. between driveways).

Three-lane cross-sections
Three-lane cross-sections

This guideline does not refer to third lanes used as passing, turning or climbing lanes in rural areas.

Table 940.11 Three-Lane Guidelines
Roadway Classification In Current and Projected Urban AreasIn Rural Areas
Major, Freeway Not applicable Not applicable
Major, Non-Freeway May be used when appropriate when AADT in design year is less than 17,500 Not recommended
Minor May be used when appropriate when AADT in design year is less than 17,500 Not recommended
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