Access Lines

An access line is a telecommunications link or telephone line connecting the central office or local switching center of a telephone company to the end user. Access lines are sometimes referred to as local routing numbers (LRNs), wireline loops, or switched access lines, and they do not include telephone numbers used for wireless services. Access lines provide access to a residence or business over twisted-pair copper wire, coaxial cable, or optical fiber. The Federal Communications Commission reported that as of December 31, 2005, there were approximately 175.5 million switched access lines in the United States. Access lines are normally assigned in prefixes or 1000-blocks classified by Telcordia as POTS (“Plain Old Telephone Service”), and most frames used for generating telephone samples are restricted to POTS prefixes and 1000-blocks.

Approximately two thirds of all access lines connect to a residence, which suggests that two thirds of working numbers in a telephone sample should be residential. Many business access lines are in dedicated prefixes or banks and do not appear in a list-assisted random-digit dialing (RDD) telephone sample. However, since a single business will frequently have multiple access lines, such as rollover lines, direct inward dial lines, fax lines, and modem lines, those access lines that are not in dedicated banks will appear in an RDD sample, substantially increasing the number of ineligible units.

A household also may have more than one access line. Over the years some households added additional access lines for children or home businesses. The increased use of home computers and residential fax machines in the 1990s further increased the number of residences with two or more access lines. Because multiple lines meant multiple probabilities of selection for a household, telephone surveys have regularly included a series of questions designed to determine the number of access lines or telephone numbers in a household. Between 1988 and 2001, the percentage of households with one or more nonprimary lines grew from approximately 2% to 26%. Dedicated computer lines have caused problems for telephone survey researchers, since these lines typically ring but are never answered, resulting in unknown eligibility status. Consequently, survey questions designed to determine the number of access lines have had to be adjusted to determine the number of lines that would ever be answered. Since 2001, the number of residential access lines has been declining. Many households have given up second lines and moved from dial-up Internet service to broadband service. Other households have opted to substitute wireless service for wireline service for some or all of their access lines. Current estimates suggest that, in 2007, 13% of households had only wireless telephone service.

Although an access line usually connects to a business or a residence, it may also connect to a pay phone, fax machine, or modem. Access lines can be used to obtain directory assistance, connect to Internet service providers, and order special programming from a cable or satellite service provider. An access line may not always connect to a specific location or device. Call forwarding allows a telephone call to be redirected to a mobile telephone or other telephone number where the desired called party is located. An access line can also be ported to another access line. Local number portability is the ability of subscribers to keep their existing telephone numbers when changing from one service provider to another. Porting requires two 10-digit numbers or access lines for each telephone number that is switched. One is the original subscriber number and the other is the number associated with the switch belonging to the new carrier. Finally, nascent Voice over Internet Protocol (VoIP) technologies and “virtual” phone numbers allow an access line to connect to either a telephone or computer that may or may not be located at the physical address associated with that access line or switch.

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