The City of Tucson, Arizona, enacted a city zoning ordinance limiting commercial speech by prohibiting outdoor advertising display signs – including billboards. On-site signs at a business location were exempted from this rule. The city based the restriction on traffic safety and aesthetics. Metromedia, Inc., a company in the business of leasing commercial billboards to advertisers, sued the City of Tucson, alleging that the zoning ordinance is unconstitutional. Is it? Explain.