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Access Management on Crossroads in the Vicinity of Interchanges, NCHRP Synthesis 332 by Marc A. Butorac and Jerilyn C. Wen, (Transportation Research Board, 2101 Constitution Avenue, N.W., Washington, D.C. 20418; ph. 202-334-2934; http://www.national-academies.org/trb/bookstore) (2004)


90% manage access

only a minority of states legislate access rules

the majority of state departments of transportation rely on the 100-ft urban and 300-ft rural spacing guidelines

General Practices

Nearly 90% of the surveyed state and provincial transportation agencies and toll authorities currently manage, to varying degrees, access to crossroad facilities upstream and downstream of the interchange terminals.

Only 9 of the 36 transportation agencies responding to the survey have their access spacing standards supported directly by legislation and adopted through regulation. In addition, six have had their access spacing standards on crossroads adopted as regulations.

Only 60% of the surveyed agencies indicated that they operate an integrated process that maintains the safety and efficiency of an interchange through access management (an integrated process is based on and includes planning, and it continues through design and into operations and maintenance).

Access Spacing Standards

Agencies use a wide range of factors to determine the appropriate spacing to the first access location downstream and upstream of the interchange terminal including the surrounding land use and environment, crossroad classification, interchange form,

public and private access, type of downstream access point, downstream storage requirements, cross section, design speed, volume, cycle length, cost and economic impacts, level of interchange importance, and crossroad jurisdiction.

The majority of state departments of transportation rely on the 100-ft urban and 300-ft rural spacing guidelines provided in the 1991 AASHTO publication, A Policy on Geometric Design of Highways and Streets. However, no underlying rationale for these spacing distances is presented within that document.

Access spacing standards for crossroad facilities vary in distance, from basically zero to 1,320 ft; however, only 50% of the transportation agencies with such standards had a specific methodology that was used to determine the actual distances.

Access Control Techniques

Nine primary access control techniques-positive control, acquisition, legislation and regulation, intergovernmental coordination, planning, operational, design, land use, and local agency regulations-were found to be commonly deployed by transportation agencies on crossroad facilities.

The most successful access control techniques found were those based on adopted legislation and/or regulations and implemented through proper and thorough land use and transportation planning, and fundamentally strong public involvement processes.

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