ADA issues tender for Riyadh metro O&M; tunnelling begins on six lines April 29, 2015 | Middle East & Africa News Saudi Arabia’s ArRiyadh Development Authority (ADA) has issued a tender for the operation and maintenance (O&M) of the upcoming Riyadh metro, which will comprise six lines covering 176.6 km ... This content is available to only subscribers. Username or E-mail Password Remember Me Forgot Password