Auxiliary Lanes
This subsection describes the basic use and functional criteria associated with auxiliary lanes. Auxiliary lanes consist of left-turn and right-turn movements, deceleration, acceleration, and their associated transitions and storage requirements. Left-turn movements may pose challenges at driveways and street intersections. They may increase conflicts, delays, and crashes and often complicate traffic signal timing. These problems are especially acute at major highway intersections where heavy left-turn movements take place, but also occur where left-turn movements enter or leave driveways serving adjacent land development. As with left-turn movements, right-turn movements pose problems at both driveways and street intersections. Right-turn movements increase conflicts, delays, and crashes, particularly where a speed differential of 10 mph or more exists between the speed of through traffic and the vehicles that are turning right.
Table 2-3 presents thresholds for auxiliary lanes. These thresholds represent examples of where left turn and right turn lanes should be considered. Refer to the TxDOT Roadway Design Manual, Chapter 3, for proper acceleration and deceleration lengths.
Median Type | Left Turn to or from Property | Right Turn to or from Property (5) | ||
Acceleration | Deceleration | Acceleration | Deceleration | |
Non-Traversable (Raised Median) | (2) | All | Right turn egress > 200 vph (4) |
|
Traversable (Undivided Road) | (2) | (1) | Same as above | Same as above |
1) Refer to Table 3-11, TxDOT Roadway Design Manual, for alternative left-turn-bay operational considerations. (2) A left-turn acceleration lane may be required if it would provide a benefit to the safety and operation of the roadway. A left-turn acceleration lane would interfere with the left-turn ingress movements to any other access connection. (3) Additional right-turn considerations:
(4) The acceleration lane should not interfere with any downstream access connection.
(5) Continuous right-turn lanes can provide mobility benefits both for through movements and for the turning vehicles.1 Access connections within a continuous right turn lane should meet the spacing requirements found in Table 2-2. However, when combined with crossing left in movements, a continuous right-turn lane can introduce additional operational conflicts. |
1.
Florida Department of Transportation (FDOT), Florida's Driveway Handbook, 2002.