Upon the written request of the district commission made to the boards of supervisors pursuant to subdivision 9 of § 15.2-4805, the board of supervisors may levy and collect an annual special improvements tax on all taxable real property that (i) is zoned for commercial or industrial use or used for such purposes or (ii) was unimproved at the time the district was created, regardless of zoning. Notwithstanding the provisions of Article 4 (§ 58.1-3229 et seq.) of Chapter 32 of Title 58.1, the tax shall be levied upon the assessed fair market value of the taxable real property. The rate of the special improvements tax shall not be more than $0.20 per $100 of the assessed fair market value of any taxable real estate or the assessable value of taxable leasehold property as specified by § 58.1-3203. Such special improvements taxes shall be collected at the same time and in the same manner as county taxes are collected, and the proceeds shall be kept in a separate account. All revenues received by a county pursuant to such taxes shall be paid over to the district commission for its use pursuant to this article.