Table 2 Definition of the Dummy Variables Included in the Estimated Demand Equation

Dummy variables	Period	Comment	Expected sign
Z1-Z4	1994 - 1998	They reflect the negative impact on traffic on the 4 A(2) motorway sections, derived from capacity and quality improvements on the alternative free road.	–
Z5-Z7	1992	They account for the positive impact on the 3 A(4) motorway sections, derived from the Seville World Exhibition in 1992.	+
Z8-Z11	1995 - 1998	They reflect the negative impact on traffic on 4 A(7) motorway sections as a consequence of the extension of an alternative tollway.	–
Z12, Z14, and Z16	1993 - 1998	They reflect the negative impact on traffic on 3 A(7) motorway sections, derived from the opening of an alternative free motorway.	–
Z13, Z15, and Z17-Z24	1990 - 1998	They account for the positive impact on traffic on 10 A(7) motorway sections, due to the extension of this motorway.	+
Z25	1996 - 1998	It reflects improvements in the free alternative motorway network for the first of the A(19) motorway sections.	–
Z26, Z27, and Z28	1994 - 1998	They account for the positive impact on traffic on the 3 A(66) sections as a consequence of the improvement and extension of the motorway.	+

Notes: In Spain, the motorways (autopistas) are identified by the letter "A" followed by a number in parentheses.

These variables take the value 1 in the reported period; otherwise they are 0.

Bureau of Transportation Statistics