4.0 Geometric and Safety Design

4.4.3 Recommended Guidelines

Lane and Shoulder Width Design Issues

The AASHTO "Green Book" does not specifically mention anything related to toll lane widths. Consequently, the AASHTO recommended 12 foot width should be adopted for express lanes. As described above, conventional plaza lanes have historically been less than 12 feet, although this is not necessarily applicable to newer conventional plaza designs. Twelve (12) foot wide toll lanes can comfortably accommodate larger vehicles and elderly drivers than in narrower lanes where they may come in contact with toll island equipment. Oversized loads (up to 14 feet wide) need to be accommodated in at least one lane, subject to state/local permit requirements. Oversized vehicles are usually handled in the far right lane where a shoulder can be used to provide additional lane width.

An ITE report recommends that manual, ACM/ATM, and dedicated ETC lanes have the following minimum widths:

Lanes with less than 10% trucks	10 feet minimum
Lanes with 10-30% trucks	11 feet minimum
Lanes with 30% trucks	12 feet minimum

Some of the significant issues to consider in establishing lane and shoulder widths include the following:

speed reduction through the toll lane,
potential for damage to vehicle and toll equipment located near the edge of the toll island,
provisions for handling large trucks and over-sized vehicles,
provisions for passage of maintenance vehicles,
refuge for disabled vehicles in express lanes,
refuge for law enforcement vehicles for on-site violation enforcement details and homeland security functions,
provisions for emergency vehicle access to express lanes during peak-hour periods,
in cases with insufficient median width only, possible tapered reduction to the inside express lane shoulder width to accommodate gantry supports,
capacity loss due to partial or full lane blockage,
available right of way and overall plaza width.

Lane and Shoulder Width Guidelines

Guideline	Lane and Shoulder Width Design Guideline 1
Title	Manual and ACM/ATIM Lanes
Text	Toll lane width should be a minimum of 11 feet, with 12 feet desirable to accommodate large vehicles.
Commentary	A far right manual lane width of at least 16 feet should be considered for over-sized vehicles. For existing facilities, this same objective may be achieved by a 12 foot lane and a 4 foot shoulder.

Guideline	Lane and Shoulder Width Design Guideline 2
Title	Dedicated ETC Lanes
Text	Toll lane width should be a minimum of 11feet, with 12 feet desirable to accommodate larger vehicles, if permitted.
Commentary	None

Guideline	Lane and Shoulder Width Design Guideline 3
Title	Express ETC Lanes
Text	Toll lane and shoulder widths should match the typical section design used for the approaching roadway.
Commentary	Some shoulder restriction may be needed to the inside shoulder to accommodate a bridge or gantry structure foundation used to support overhead toll and violation enforcement equipment when the median width is insufficient. This isolated shoulder restriction should be tapered and the shoulder width reduction should be limited in length to minimize the impact on an emergency vehicle using the shoulder to bypass congested traffic conditions subject to the shoulder width being sufficient for vehicle travel.

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