While a planned extension of Metrorail may boost land values throughout Tysons Corner, some say the presence of a track looming over homes and businesses could lessen the hoped-for jump in values.

Real estate values likely will be less than they would have been if Metro came to the area, but the trains were not rumbling over four miles of elevated track through Tysons — the current plan of Gov. Timothy Kaine after he scrapped a preferred tunnel option this week.